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Is there an adhesive that could used for larval fish?

Is there an adhesive that could used for larval fish?


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I am currently working on an experimental design that requires a larval fish (~ 4mm long) to be affixed on a metal wire tip on its dorsal side. Now, I was thinking of a glue or adhesive to do the job, but it doesn't have to be strictly these, anything that sufficiently attaches the fish to the metal wire tip would do. The glue/adhesive would have to work well on wet surface and, ideally, something that is not toxic. Any advice or ideas are welcome.


You could try methyl cellulose, which my lab and others use. It's not exactly an adhesive, but it is quite viscous. It's common enough that it's in the Zebrafish Book: https://wiki.zfin.org/display/prot/Methyl+Cellulose+Mounting . Obviously, be sure whatever you do is approved by your animal care and use committee.


Hidden World Just Below the Surface: Scientists Discover Ocean “Surface Slicks” Are Nurseries for Diverse Fishes

Composite image showing just a small portion of the remarkable diversity of larval and juvenile fishes and invertebrates found living in surface slick nurseries along West Hawaii Island. Credit: Larval photos: Jonathan Whitney (NOAA Fisheries), Slick photo: Joey Lecky (NOAA Fisheries)

The open ocean is a harsh place for newborn fishes. From the minute larvae hatch from their eggs, their survival depends upon finding food and navigating ocean currents to their adult habitats–all while avoiding predators. This harrowing journey from egg to home has long been a mystery, until now.

An international team including scientists from the Arizona State University Center for Global Discovery and Conservation Science (GDCS), NOAA’s Pacific Islands Fisheries Science Center, and the University of Hawai’i at Mānoa have discovered a diverse array of young marine animals finding refuge within so-called ‘surface slicks’ in Hawai’i. Surface slicks create a superhighway of nursery habitat for more than 100 species of commercially and ecologically important fishes, such as mahi-mahi, jacks, and billfish. The study was published today in the journal Scientific Reports.

Surface slicks are naturally occurring ribbon-like bands of smooth water at the ocean surface and have long been recognized as an important part of the seascape. To unravel their secrets, the research team conducted more than 130 plankton net tows inside the surface slicks and surrounding waters along the leeward coast of Hawai’i Island, while studying ocean properties. In these areas, they searched for larvae and other plankton that live close to the surface. They then combined those in-water surveys with a new satellite-based technique to map the location of the slicks. This technique involved using more than 100 shoebox-sized satellites, built and operated by GDCS partner Planet, to discern textural sea surface differences between surface slicks and regular seawater.

“In an earlier study, our surface slick mapping suggested strong along-coast connectivity of ocean habitats. In our latest study reported here, we populated those satellite-based slick maps with the billions of animals, organic debris, and microplastics that make up the slicks”, said Greg Asner, GDCS director and co-author of the study.

Though the slicks only covered around eight percent of the ocean surface in the 380-square-mile-study area, they contained an astounding 39 percent of the study area’s surface-dwelling larval fish over 25 percent of its zooplankton, and 75 percent of its floating organic debris, such as feathers and leaves. Larval fish densities in surface slicks off West Hawai’i were, on average, over 7 times higher than densities in the surrounding waters.

The study showed that surface slicks function as a nursery habitat for marine larvae of at least 112 species of commercially and ecologically important fishes, as well as many other animals. These include coral reef fishes, such as jacks, triggerfish, and goatfish pelagic predators, for example, mahi-mahi deep-water fishes, such as lanternfish and various invertebrates, such as snails, crabs, and shrimp.

The remarkable diversity of fishes found in slick nurseries represents nearly 10 percent of all fish species recorded in Hawai’i. The total number of taxa in the slicks was twice that found in the surrounding surface waters, and many fish taxa were between 10 and 100 times more abundant in slicks.

“We were shocked to find larvae of so many species, and even entire families of fishes, that were only found in surface slicks.,” said Jonathan Whitney, a research marine ecologist for NOAA and lead author of the study. “The fact that surface slicks host such a large proportion of larvae, along with the resources they need to survive, tells us they are critical for the replenishment of adult fish populations,” he added.

In addition to providing crucial nursing habitat for various species and helping maintain healthy and resilient coral reefs, slicks create foraging hotspots for larval fish predators and form a bridge between coral reef and pelagic ecosystems.

“Our findings are part of an important story forming around the role of biological surface slicks in maintaining coral reefs. The sheer biodiversity and biomass of the slicks, combined with their oceanic movement along the shore, form a superhighway for species that connects and effectively generates an interconnected, regional reef ecosystem,” proclaimed Asner.

While slicks may seem like havens for all tiny marine animals, there’s a hidden hazard lurking in these ocean oases: plastic debris. Within the study area, 95 percent of the plastic debris collected into slicks, compared with 75 percent of the floating organic debris. Larvae may get some shelter from plastic debris, but it comes at the cost of chemical exposure and incidental ingestion.

In certain areas, slicks can be dominant surface features, and the new research shows these conspicuous phenomena hold more ecological value than meets the eye.

“Our work illustrates how these oceanic features (and animals’ behavioral attraction to them) impact the entire surface community, with implications for the replenishment of adults that are important to humans for fisheries, recreation, and other ecosystem services,” said Margaret McManus, co-author, Professor and Chair of the Department of Oceanography at the University of Hawai’i at Mānoa. “These findings will have a broad impact, changing the way we think about oceanic features as pelagic nurseries for ocean fishes and invertebrates.”

Reference: “Surface slicks are pelagic nurseries for diverse ocean fauna” by Jonathan L. Whitney, Jamison M. Gove, Margaret A. McManus, Katharine A. Smith, Joey Lecky, Philipp Neubauer, Jana E. Phipps, Emily A. Contreras, Donald R. Kobayashi and Gregory P. Asner, 4 February 2021, Scientific Reports.
DOI: 10.1038/s41598-021-81407-0


Prey-size plastics are invading larval fish nurseries

New research shows that many larval fish species from different ocean habitats are ingesting plastics in their preferred nursery habitat.

Many of the world's marine fish spend their first days to weeks feeding and developing at the ocean surface. Larval fish are the next generation of adult fish that will supply protein and essential nutrients to people around the world. However, little is known about the ocean processes that affect the survival of larval fish. NOAA's Pacific Islands Fisheries Science Center and an international team of scientists conducted one of the most ambitious studies to date to learn where larval fish spend their time and what they eat while there.

The study will be published November 11, 2019 in the journal Proceedings of the National Academy of Sciences. The researchers combined field-based plankton tow surveys and advanced remote sensing techniques to identify larval fish nursery habitats in the coastal waters of Hawai'i.

The team found that surface slicks contained far more larval fish than neighboring surface waters. Surface slicks are naturally occurring, ribbon-like, smooth water features at the ocean surface. They are formed when internal ocean waves converge near coastlines and are observed in coastal marine ecosystems worldwide. The surface slicks also aggregate plankton, which is an important food resource for larval fish.

"We found that surface slicks contained larval fish from a wide range of ocean habitats, from shallow-water coral reefs to the open ocean and down into the deep sea--at no other point during their lives do these fish share an ocean habitat in this way," said Dr. Jonathan Whitney, a marine ecologist for the Joint Institute for Marine and Atmospheric Research and NOAA, and co-lead of the study. "Slick nurseries also concentrate lots of planktonic prey, and thereby provide an oasis of food that is critical for larval fish development and survival."

Larval fish in the surface slicks were larger, well-developed, and had increased swimming abilities. Larval fish that actively swim will better respond and orient to their environment. This suggests that tropical larval fish are actively seeking surface slicks to capitalize on concentrated prey.

Unfortunately, the team also discovered that the same ocean processes that aggregated prey for larval fish also concentrated buoyant, passively floating plastics. "We were shocked to find that so many of our samples were dominated by plastics," said Dr. Whitney.

Plastic densities in these surface slicks were, on average, eight times higher than the plastic densities recently found in the Great Pacific Garbage Patch. After towing the net 100 times, they found that plastics were 126 times more concentrated in surface slicks than in surface water just a couple hundred yards away. There were seven times more plastics than there were larval fish.

The majority of the plastics found in surface slicks were very small (less than 1 mm). Larval fish prefer their prey this size. After dissecting hundreds of larval fish, the researchers discovered that many fish species ingested plastic particles. "We found tiny plastic pieces in the stomachs of commercially targeted pelagic species, including swordfish and mahi-mahi, as well as in coral reef species like triggerfish," said Dr. Whitney. Plastics were also found in flying fish, which apex predators such as tunas and most Hawaiian seabirds eat.

While recent evidence shows that adult fish ingest plastic, this is the first study to show that larval coral reef fish and pelagic species are also consuming plastic, as early as days after they are spawned.

"Larval fish are foundational for ecosystem function and represent the future of adult fish populations," said Dr. Jamison Gove, a research oceanographer for NOAA and co-lead of the study. "The fact that larval fish are surrounded by and ingesting non-nutritious toxin-laden plastics, at their most vulnerable life-history stage, is cause for alarm."

Researchers are unclear just how harmful plastic ingestion is to larval fish. In adult fish, plastics can cause gut blockage, malnutrition, and toxicant accumulation. Larval fish are highly sensitive to changes in their environment and food. Prey-size plastics could impact development and even reduce survivorship of larval fish that ingest them.

The researchers also used satellites to measure the size and distribution of the surface slicks across their study region in Hawai'i. Even when viewed from space, surface slicks were distinctly recognizable from the rest of the ocean. The researchers found that surface slicks comprise less than 10% of ocean surface habitat but are estimated to contain 42.3% of all surface dwelling larval fish and 91.8% of all floating plastics. "Surface slicks had never been mapped before, but we knew it would be vital to scaling up the field-based study. Our new method developed for this study can be applied anywhere in the world," noted co-author Dr. Greg Asner of Arizona State University's Center for Global Discovery and Conservation Science.

"Biodiversity and fisheries production are currently threatened by a variety of human-induced stressors such as climate change, habitat loss, and overfishing. Our research suggests we can likely now add plastic ingestion by larval fish to that list of threats," said Dr. Gove.

Some scientists criticize the attention on plastic pollution. They say that it is distracting society from tackling more known and severe threats to global fisheries.

"We agree that curbing carbon emissions and finding more sustainable ways to fish must be a priority, but our findings suggest further investigation is needed to understand the effects of plastic ingestion by larval fish on individuals and populations," said Dr. Gareth Williams, Associate Professor in Marine Biology at Bangor University (U.K.) and co-author of the study. "We as a society have the ability to make changes that would alleviate the stress on ecosystems imposed by our activities. We can and should start making those changes now, to limit stress to already severely threatened marine life."

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


Prey-Size Plastics are Invading Larval Fish Nurseries

Many of the world’s marine fish spend their first days or weeks feeding and developing at the ocean surface. Larval fish are the next generation of adult fish that will supply protein and essential nutrients to people around the world. However, little is known about the ocean processes that affect the survival of larval fish. NOAA’s Pacific Islands Fisheries Science Center and an international team of scientists conducted one of the most ambitious studies to date. They wanted to learn where larval fish spend their time and what they eat there.

The study was published today in the journal Proceedings of the National Academy of Sciences. The researchers combined field-based plankton tow surveys and advanced remote sensing techniques. These tools identified larval fish nursery habitats in the coastal waters of Hawai‘i.

The team found that surface slicks contained far more larval fish than neighboring surface waters. Surface slicks are naturally occurring, ribbon-like, smooth water features at the ocean surface. They form when internal ocean waves converge near coastlines in marine ecosystems worldwide. The surface slicks also aggregate plankton, which is an important food resource for larval fish.

Numerous larval fish, often just weeks old, had plastics in their stomachs, including (top left, then clockwise) mahi-mahi, flying fish, spearfish, jacks, triggerfish (two sizes), and damsels. Photo: NOAA Fisheries/Jonathan Whitney. Photo: NOAA Fisheries/Jonathan Whitney.

“We found that surface slicks contained larval fish from a wide range of ocean habitats, from shallow-water coral reefs to the open ocean and down into the deep sea—at no other point during their lives do these fish share an ocean habitat in this way,” said Dr. Jonathan Whitney, a marine ecologist for the Joint Institute for Marine and Atmospheric Research and co-lead of the study. “Slick nurseries also concentrate lots of planktonic prey, and thereby provide an oasis of food that is critical for larval fish development and survival.”

Larval fish in the surface slicks were larger, well-developed, and had increased swimming abilities. Larval fish that actively swim will better respond and orient to their environment. This suggests that tropical larval fish are actively seeking surface slicks to capitalize on concentrated prey.

Unfortunately, the team also discovered that the same ocean processes that aggregated prey for larval fish also concentrated buoyant, passively floating plastics. “We were shocked to find that so many of our samples were dominated by plastics,” said Dr. Whitney.

Plastic densities in these surface slicks were, on average, eight times higher than the plastic densities recently found in the Great Pacific Garbage Patch. The researchers towed the net 100 times. They found that plastics were 126 times more concentrated in surface slicks than in surface water just a couple hundred yards away. There were seven times more plastics than there were larval fish.

A scribbled filefish in a sea of plastics sampled from surface slicks off Hawai‘i Island. Photo courtesy of David Liittschwager.

The majority of the plastics found in surface slicks were very small (less than 1 mm). Larval fish prefer their prey this size. After dissecting hundreds of larval fish, the researchers discovered that many fish species ingested plastic particles. “We found tiny plastic pieces in the stomachs of commercially targeted pelagic species, including swordfish and mahi-mahi, as well as in coral reef species like triggerfish,” said Dr. Whitney. Plastics were also found in flying fish, which apex predators such as tunas and most Hawaiian seabirds eat.

Larval flying fish (top) and triggerfish (bottom) with magnified plastics that fish ingested (left). Dime shown for scale. Photo: NOAA Fisheries/Jonathan Whitney.

Recent evidence shows that adult fish ingest plastic. This is the first study to show that larval coral reef fish and pelagic species are also consuming plastic, as early as days after they are spawned.

“Larval fish are foundational for ecosystem function and represent the future of adult fish populations,” said Dr. Jamison Gove, a research oceanographer for NOAA and co-lead of the study. “The fact that larval fish are surrounded by and ingesting non-nutritious toxin-laden plastics, at their most vulnerable life-history stage, is cause for alarm.”

Researchers are unsure of how harmful plastic ingestion is to larval fish. In adult fish, plastics can cause gut blockage, malnutrition, and toxicant accumulation. Larval fish are highly sensitive to changes in their environment and food. Prey-size plastics could impact development and even reduce survivorship of larval fish that ingest them.

The researchers measured the size and distribution of the surface slicks using satellites. Even when viewed from space, surface slicks are distinct from the rest of the ocean. The researchers found that surface slicks comprise less than 10 percent of ocean surface habitat. However, they are estimated to contain about 42 percent of all surface dwelling larval fish and nearly 92 percent of all floating plastics.

“Surface slicks had never been mapped before, but we knew it would be vital to scaling up the field-based study. Our new method developed for this study can be applied anywhere in the world,” noted co-author Dr. Greg Asner of Arizona State University’s Center for Global Discovery and Conservation Science.

“Biodiversity and fisheries production are currently threatened by a variety of human-induced stressors such as climate change, habitat loss, and overfishing. Our research suggests we can likely now add plastic ingestion by larval fish to that list of threats,” said Dr. Gove.

Some scientists criticize the attention on plastic pollution. They say that it is distracting society from tackling more known and severe threats to global fisheries.


Lepisosteus platyrhincus

Florida gar. Photo © George Burgess

These are the smaller fish in the gar family, growing to about 34 inches on average. They inhabit the streams and lakes of Florida and lower Georgia, preferring muddy bottoms and vegetation to ambush prey. Their small fins are set far back on their elongated torpedo-shaped bodies that start with a pointed, toothy snout and end with an irregular caudal (tail) fin. They are not particularly valued for recreational fishing, and their roe is toxic to humans, so they are only threatened by habitat loss.

Order – Lepisosteiformes Family – Lepisosteidae Genus – Lepisosteus Species – platyrhincus

Common Names

The English language common name is Florida gar. Other common names include Florida-pansergedde (Danish), Floridabengädda (Swedish), and Floridanluuhauki (Finnish).

Importance to Humans

The Florida gar is not normally considered a sport fish but it commonly takes a hook and produces a worthy fight on light tackle. Gars are only occasionally eaten and there is no market for their flesh. Because of their ravenous feeding habits, Florida gars sometimes are blamed for poor fishing. The gar’s sharp teeth and bony jaws often force anglers to opt to use a wire leader while using shredded nylon floss to entangle the gar’s teeth. Another fishing method uses a baited wire noose that is pulled tight over the jaws once the gar has nosed its way towards the bait.

This fish is often seen in public aquaria , however it is unsuitable for home aquariums due to its large size and large tank requirements.

Conservation

The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species.

Geographical Distribution

World distribution map for the Florida gar

Florida gar are found from the Ocklockonee River drainage, Florida and Georgia, southward through peninsular Florida and northward to Savannah River drainage, Georgia.

Habitat

Florida gars are common in medium to large lowland streams, canals, and lakes with mud or sand bottoms and an abundance of underwater vegetation. They often congregate in spring-fed rivers of Florida. This is in contrast to their close relative, the longnose gar (L. osseus) that often cruise open water.

Biology

Florida gar. Photo © George Burgess

Distinctive Features
The gar’s body is covered with enamel-hard, diamond-shaped plates called ganoid scales. The American Indians once used the dried hides of the Florida gar for goods and the scales as arrowheads. The Florida and spotted gars are distinguishable from each other primarily by the snout length. The distance from the front of the eye to the back of the gill cover is less than 2/3 the length of the snout in the Florida gar, while it is more than 2/3 of the length in the spotted gar. The Florida gar lacks bony scales on the throat.

The snout is elongated, with the nostrils located at the tip. The gar breathes with its gills and with its special lunglike air bladder. Due to the highly vascularised air bladder that is connected to its throat, the gar may survive in hot, stagnant waters that might not have sufficient oxygen for most other species of fish.

Spotted gar are often confused with the Florida gar. Photo courtesy U.S. Fish and Wildlife Service

Coloration
Florida gars have irregular round, black spots on the top of the head and over the entire body and fins. Their coloration is olive-brown along the back and upper sides with a white-to-yellow belly. The young may have dark stripes along back and sides.

Dentition
The Florida gar has a broad snout with a single row of irregularly spaced canines on the upper and lower jaws.

Denticles
Gars, as well as bowfins, paddlefishes, and sturgeons, have thick ganoid scales. These scales tend to be diamond-shape and are interlocking. Each scale consists of a bony base layer and an outer layer of ganoine which is an inorganic bone salt. The main purpose of ganoid scales is “armored” protection against predators.

Size, Age & Growth
Florida gars are thought to grow rapidly. Adult size is approximently 13- 34 inches (.33-.86 m) total length. The maximum size recorded is 52.4 inches (1.33 m TL). The Florida all-tackle record Florida gar weighted 7 pounds (3.2 kilograms). Females reach larger sizes than males.

Food Habits
Young Florida gars feed on zooplankton, insect larvae and small fish. Adults feed primarily on fish, along with some crustaceans and insects. The gar floats silently near the surface of the water, disguised as a stick or log. When it comes upon a fish, it propels itself slowly forward with a flick of its fins. Once into position the gar snaps its head sideways and secures the prey with its sharp teeth, then it slowly repositions the fish so that it can be swallowed headfirst.

Reproduction
Florida gar spawn mostly during the months of April and May, but spawning may continue into October. Nests are not built instead the female spawns by distributing her adhesive eggs in shallow pools, weedy backwaters, or shallow riffles. The eggs are greenish-colored and are fertilized by two or more attending males.

The newly hatched larva has an adhesive disc on the front of the blunt snout, which it uses to attach itself to gravel or vegetation. The larva remains attached until reaching an approximate length of ¾ inches. As a juvenile, the gar has a fragile fin that extends along the upper edge of the tail and vibrates constantly. The fin is lost during the first year of life.

American alligators are a potential predator, Image courtesy U.S. Geological Survey

Predators
Florida gar eggs are highly toxic to humans and animals, including birds. However, the juveniles are susceptible to a variety of fish and bird predators. Adults fall prey to alligators (Alligator mississippiensis).

Parasites
The cestode Perezitrema singularis has been recorded as an intestinal parasite of the Florida gar.

Taxonomy

In 1842, DeKay described the Florida gar as Lepisosteus platyrhincus. Synonyms for this species include Cylindrosteus megalops Fowler 1911. The genus name, Lepisosteus, is derived from the Greek “lepis” meaning scale and “osteon” meaning bone bony scaled.


Acknowledgements

Research carried out in this study followed animal care and use guidelines provided by the Smithsonian Institution.

Sincere thanks to the following for providing significant specimens, tissue and/or data: K. Hartel, A. Williston (MCZ), E. Wiley, A. Bentley (KU), B. Cowen (RSMAS), I. Byrkjedal (ZMUB), N. Merrett, J. Badcock, J. Maclaine (IOS/BMNH), E. Bertelsen † , and P. Møller (ZMUC) images: B. Robison (MBARI), D. Hughes, Y. Morita and M. Nakamachi. Numerous others who have helped in many ways are listed in the electronic supplementary material.


The Secret Tuna Nursery

It was a little after 10 p.m., and several hundred miles off the coast of Massachusetts, Chrissy Hernandez was counting eyeballs.

Scattered across a dinner plate-sized sieve in front of her was the harvest from yet another tow with a fine-meshed net. Hernandez, a graduate student in the MIT-WHOI Joint Program in Oceanography, shone a light across the sieve, looking for the telltale shine of larval fish eyes. She was hunting for one species in particular—Atlantic bluefin tuna.

Bluefin tuna are the largest species of tuna, growing up to ten feet long and more than a thousand pounds. Their population has been severely depleted by overfishing, as their meat is prized for sushi and can sell at exorbitant prices (one fish sold for more than $1.7 million in Japan in 2013).

A key way to help conserve the species is to protect areas where they go to spawn. But to do that, “you need to know where they spawn,” said Joel Llopiz, a biologist at Woods Hole Oceanographic Institution (WHOI) and Hernandez’s advisor.

In the Atlantic, bluefin tuna generally split into two stocks, which are managed separately. The eastern stock spawns in the Mediterranean Sea, and the western stock spawns in the Gulf of Mexico.

But in the summer of 2017, Hernandez wasn’t in either of these recognized spawning grounds. She was in a third, previously unknown spawning area. It’s tucked into the gap between the continental shelf off the U.S. Eastern Seaboard and the Gulf Stream current as it peels away from the coast—an area known as the Slope Sea.

Some scientists had suspected that the Slope Sea could be a potential spawning ground because they had tracked tagged tuna to this location when the waters were warm enough for spawning. But adult bluefin tuna can swim up to 40 miles per hour and the tags aren’t that accurate. The fish could have just been passing through. Then in 2013, larval bluefin tuna were found in several locations in the Slope Sea during a sampling cruise run by the National Oceanic and Atmospheric Administration (NOAA).

The findings from the cruise were published in 2016, at just the right time for Hernandez. “It was the spring of the first year of my Ph.D. program, and I wasn’t sure what I wanted to do,” she said. “What was going to keep me excited about science?”

The discovery of a potentially new spawning location was definitely exciting. But there’s a big difference between finding larvae and showing that these fish grow up to contribute significantly to the bluefin population. The Slope Sea is a very different environment from the other two spawning locations. Could fish hatched there actually grow and survive, or would they all die off?

Caught in the currents

The first few weeks of a bluefin tuna’s life aren’t easy. A female tuna can lay millions of eggs, but only a small percentage of hatchlings will make it to adulthood. The new larvae are tiny, only a few millimeters long, and they are easily swallowed by a plethora of plankton-eaters. Even if they manage to avoid being eaten, an influx of water that is too warm or too cold can kill them as they are swept along by the currents around them.

The Slope Sea, which is known for both fluctuating currents and temperatures, is a hard place to survive.

“And it’s very close to the Gulf Stream, which is bad for spawning,” said Llopiz. “Your larvae are going to get shot off toward England by the current, and will end up too far away to make it back to the nursery grounds.”

Young tuna could also wind up along the continental shelf, where the waters are too cold for survival.

On the other hand, some of the currents in the Slope Sea might actually help the tuna larvae. As the Gulf Stream wavers along the Slope Sea’s southern edge, it spins off rotating currents to the north, known as eddies or warm-core rings, that can linger for months. As their name suggests, these rings trap warm water in their centers. If that water is the right temperature, the circular motion could cocoon larvae safely within the Slope Sea until they are able to swim independently.

The Slope Sea’s variable currents and fluctuating temperatures makes it a complicated problem to determine if larvae can survive there. Scientists can take measurements of the water temperatures and currents as they study the area, but these only provide brief snapshots of information in one place at one time.

“Field data on currents are valuable,” Llopiz said. “It’s just that you can’t be everywhere at the same time.”

To figure out whether the Slope Sea could be a viable spawning ground for bluefin tuna, the biologists needed a picture of what was happening in the entire area over the course of several months.

Fortunately, Llopiz knew people who could build exactly that.

Biology meets physics

A few years earlier, Llopiz had received an email from two physical oceanographers at WHOI, Larry Pratt and Irina Rypina, who were examining another longstanding ocean larval mystery: how American eels get from their spawning areas in the Sargasso Sea to the mouths of Eastern Seaboard rivers where they spend their adult lives.

Pratt had seen an article in The New York Times claiming that larval eels simply drifted from the middle of the Atlantic to the coast of Maine. He and Rypina study ocean currents, and they had their doubts. But they were not experts in all the biological factors involved, so they enlisted Llopiz.

“Teaming up with physical oceanographers is great,” Llopiz said. “To be able to know what the currents are doing everywhere all the time is mind-blowing. And when these little fish are at the mercy of ocean currents, it’s super valuable information.”

The trio wound up collaborating on a study using a numerical model of currents in the Atlantic Ocean to investigate this mysterious migration. Since then, they have kept an eye out for other opportunities to combine their skills.

“Joel was just telling us about the tuna problem,” Rypina said, “and we thought it might be a good thing to try to model.”

Rypina and Pratt study the physics of ocean movements. They focus on models that view currents as an agglomeration of individual particles of water swirling around. But tuna larvae can also be viewed as tiny individual particles, so “the method for tracking water particles can easily be adapted to track small critters,” Pratt said.

To explore the Slope Sea tuna riddle, the team needed a model that focused on that specific region the model they had used for the eels spanned a larger portion of the Atlantic. For this, they approached Ke Chen, a numerical modeler at WHOI who has been studying the physical processes in the area around the continental shelf in the Northwest Atlantic.

Chen specifically works on modeling and understanding currents on the continental shelf and in the Slope Sea, including Gulf Stream warm-core rings. To improve the accuracy of his regional model, Chen incorporates fresh water flowing out from rivers into the ocean and other processes that typically aren’t considered in open-ocean models.

“Physics tells us how the ocean is moving,” Chen said, “but you have to wonder what that means for biology.”

A virtual ocean

Chen adapted and refined models he had worked on before to create a model of water movement in the Slope Sea. He tested its accuracy against actual data collected during the 2013 NOAA cruise. They focused on the factors that would affect larvae the most: temperatures and currents in the top 30 feet of ocean, where tuna larvae are typically found.

Once they had a working model ready to go, it was time to release the fish. Virtual fish, that is.

As the model replicated the Slope Sea conditions of 2013, the scientists dropped 2,500 “larvae” into the virtual ocean every three hours between May and October and tracked them as they swirled through the currents.

Llopiz and Hernandez provided the biological information to decide whether each virtual larva survived. The larvae had to remain in the right temperatures within the Slope Sea for 25 days—an estimate of how long it might take larval tuna to grow big enough to be able to swim independently of the currents.

At the end of the model run, the researchers had found two spawning hot spots where tuna larvae had the best chance of survival. These areas were warm enough to support the larvae by the end of July, and the nearby currents kept them within the spawning ground. One was in the southwestern part of the Slope Sea, away from the swirls of the Gulf Stream, and the other was farther north, centered on the place where a warm-core ring was located in 2013.

The model identified, on average, the times and places in the Slope Sea where conditions would allow tuna larvae to thrive. The next step was to go out and see if tuna larvae are actually there.

More questions than answers

Hernandez stood on the stern of a NOAA-operated vessel holding a diamond-shaped apparatus made of canvas and bamboo, known as a drifter. She had found bluefin tuna larvae at the last three sampling locations in the ocean.

“A big warm-core ring was in the same place where the model had showed one in 2013,” Hernandez said. “We spent an entire night, well actually more like one and a half nights, doing a transect across it.”

She held a walkie-talkie in her other hand, coordinating with two shipmates who waited to deploy additional drifters.

The drifters plunged into the water, stabilizing a few meters below their buoys at the surface. They would be slowly swept away by the currents, transmitting their locations as they went.

Data from the drifters can help improve and confirm the WHOI physical oceanographers’ models.

“It’s an area of ocean that doesn’t get sampled all the time,” Hernandez said. “We really have to jump on the opportunities that do arise.”

Hernandez is using the larvae she collected to compare growth rates between the Slope Sea population and those in the Gulf of Mexico. Other researchers are looking at the genetics of the samples she collected to determine whether the Slope Sea tuna are related to the eastern or western stocks.

“There’s still a big lack of understanding of the larval ecology of Slope Sea bluefin tuna,” Llopiz said. “There’s just so much that we don’t know: how well they’re eating, how fast they’re growing, why they are where they are. There’s just a lot to learn.”

What these scientists learn will be critical for devising effective conservation strategies. The future of bluefin tuna, both in the ocean and in soy sauce, depends on it.

This research was funded by NOAA, the National Science Foundation, WHOI’s Ocean Life Institute, and WHOI’s NOAA-funded Cooperative Institute for the North Atlantic Region.


Background

Cichlids are famous for their astonishing rate of phenotypic diversification and speciation. With over 2000 described species, cichlid fish form one of the most diverse and species-rich groups of animals [1]. Lacustrine cichlids in Africa and in the Neotropics are well-known examples of adaptive radiations [2-4]. In particular, the cichlid radiations in Nicaraguan crater lakes (Figure 1, Table 1) provide a promising opportunity to study the early stages of speciation and diversification. This is because members of the Midas cichlid species complex (Amphilophus spp. or Amphilophus citrinellus spp.) have diverged repeatedly in several crater lakes, both sympatrically and allopatrically, often within a few thousand years [2,5-7]. Little is known so far about the molecular and developmental mechanisms that drive the observed phenotypic diversity between recently diverged species. The Midas cichlid complex underwent a rapid diversification within very short time spans (between 2000 and 25,000 years) and, interestingly, repeatedly evolved several adaptive traits (hypertrophied lips, elongated body shapes, dental innovations) in parallel in multiple crater lakes (Figure 1, Table 1). Therefore, Midas cichlids are an excellent model system for the comparative study of the phenotype-genotype relationship.

Range and prominent phenotypic differences of members of the Midas cichlid species complex. (A) Map of the Pacific coast of Nicaragua in Central America. Besides the large Nicaraguan lakes (Managua and Nicaragua), multiple crater lakes (Asososca Leon, Apoyeque, Xiloá, Asosoca Managua, Masaya and Apoyo) have appeared in the course of the last 25,000 years. These crater lakes have been colonized by Midas cichlids from the large lakes, resulting in new species. (B) Midas cichlids from Lake Xiloá, Amphilophus xiloaensis, the focal species of this study. (C) Three selected traits that are interesting from an evolutionary-developmental angle. In the large lakes and in many crater lakes, cichlid species and morphs show differences in coloration, body shape and lip shape.

The Midas cichlid species complex currently includes 13 described species (Table 1). Two ancestral “source” species occur in the big lakes, Lake Managua and Lake Nicaragua - Amphilophus labiatus [8] and A. citrinellus [9]. These two species repeatedly and independently colonized the much younger crater lakes of Nicaragua and gave rise to several endemic species. Since the late 1970s, many endemic crater lake species have been described. Six species, A. zaliosus, A. astorquii, A. chancho, A. flaveolus, A. globosus and A. supercilius were recently described and are endemic to crater Lake Apoyo [10-12]. Four other species of this species complex are endemic to crater Lake Xiloá (A. amarillo, A. sagittae, A. xiloaensis and A. viridis) [13,14] and one to Lake Asososca Managua, A. tolteca [14]. Despite these numerous recently-described species, more Midas cichlids certainly await formal species description [15,16].

The focal species of this study, Amphilophus xiloaensis, was first described in 2002 [13] and is endemic to Lake Xiloá (Figure 1B). This crater lake is estimated to be approximately 6100 years old [5,17]. Lake Xiloá has the greatest fish species diversity of any of the Nicaraguan crater lakes [18], including four Midas cichlids with an exceptionally high haplotype diversity relative to the lake’s age [19]. Since these species are so young, they share ancient polymorphisms [7] and some hybridization still occurs, as has been reported for African cichlids [20,21].

Many studies have assessed the early ontogeny of fishes in classic model organisms such as zebrafish, Danio rerio [22] medaka, Oryzias latipes [23] stickleback, Gasterosteus aculeatus [24] and rainbow trout, Oncorhynchus mykiss [25]. However, there have been only a few studies on cichlid fishes so far, most of which deal with the development of African species such as Oreochromis niloticus, Oreochromis mossambicus, Labeotropheus fuelleborni and Labeotropheus trewavasae [26-28]. Developmental studies of Neotropical cichlids have also been pursued, including a very detailed description of the development of the South American cichlid Cichlasoma dimerus [29-34]. Because ontogeny can differ strongly among species, there is a need for more developmental work [35].

Midas cichlids are a famous example of parallel evolution and rapid diversification [36-39]. This makes them interesting, not only from an evolutionary and ecological standpoint, but also from a developmental “evo-devo” perspective. A detailed description of the embryonic development of the Midas cichlid is still lacking. The present study aims to be a foundation for future studies examining the genetic and developmental factors that lead to phenotypic diversification among an extremely young species of a particularly species-rich lineage of cichlid fish.


2.3 FACILITIES REQUIRED FOR ARTIFICIAL REPRODUCTION OF NAKED CARP

The design recommended for the naked carp hatchery is based on the following parameters:

  • data on reproduction-biology
  • the strategy for artificial reproduction
  • local conditions and existing facilities

The naked carp hatchery will not consist of one facility only, but will comprise a complex of several components as follows:

  • An on-site pilot scale hatchery
  • A large-scale hatchery (installed in an existing hatchery)
  • Nursing ponds
  • Transporting equipment

2.3.1 On-site Pilot Scale Hatchery

The major purpose of this facility is to provide adequate conditions for the collection of the eggs and sperm, for the fertilization of the eggs and for the preparation of the fertilized eggs for transport.

However, there are also possibilities to incubate the eggs and to rear the larvae on an experimental scale here.

Since this facility should be set up near the main spawning area of the fish, as close as possible to the river, it must be easily transportable. Setting up an operation of the unit should also be simple.

Taking into account these criteria, it is proposed that a flexible system be established, as shown in Figure 2.

Water will be pumped directly from the river (without filtration and temperature control) by a portable gasoline engine driven pump. The tanks for the spawners receive their water supply direct from the pump, but a constant pressure water supply must be provided for the incubation and larval rearing equipment via an elevated head tank.

The outflow water from the various items of equipment will be collected in a drainage pipe of fairly large diameter placed just below ground level, and directed back to the river.

Most of the equipment needed for fish propagation can be installed in a 30 m 2 light-structure building or a tent, but tanks for the spawners should be placed outdoors. The tanks used for keeping spawners will be aerated by an air blower via diffusers.

An electric generator is required to provide electricity for nighttime work and for the operation of instruments and some equipment. The air blower and the electric generator should be installed in a separate building or tent, where storage space and a room for staff can also be placed.

All components of the system are designed as flexibly connected portable units which can be installed and transported easily. The equipment required for the hatchery is listed in Appendix 2, and details of hatchery construction are shown in Figures 3, 4, 5, 6 and 7.

In the four 2.5 m 3 tanks some 200 kg of spawners can be kept simultaneously. The eight 8&ndash1 hatching jars have a total capacity of about 400 000 eggs (50 000 eggs/jar) while the three 200&ndash1 larval rearing tanks are capable of holding all the newly hatched larvae from the eight jars. The 4 m 3 head tank will store enough water to supply the hatching jars and the larval rearing tanks for about one hour in the event of pump failure.

2.3.2 Large-scale Hatchery

It is proposed that fertilized eggs will be transported from the on-site pilot hatchery to the large-scale hatchery, where facilities for the incubation of larger volumes of eggs are available.

The existing hatchery at the Fisheries Research Institute in Xining is used for the propagation of Chinese carps, and, in addition to the special spawning and incubation facilities, a 600 m 2 greenhouse is also available for fish nursing.

In order to make this hatchery suitable for naked carp propagation the following major modifications are recommended:

  • expansion of the existing building
  • possibly the installation of a filter into the existing water supply system
  • installation of additional hatching jars and larval rearing tanks.

It is recommended that the existing hatchery building be enlarged by 30 m 2 . A closed pressure filter unit with high filtering velocity and a capacity of 10&ndash12 m 3 /h could be useful here. The technical specifications of a possible model are given in Figure 8. The filtered water could then be pumped into the existing head tank, where the temperature can be controlled if necessary.

The same type of hatching jars and larval rearing tanks can be used here as are specified above for the pilot scale hatchery. The installation of 32 hatching jars (into units comprising 16 jars each) and 12 larval rearing tanks are recommended. The estimated output capacity of the enlarged hatchery is 1.5&ndash2.0 million larvae/cycle.

2.3.3 Nursery Ponds

The survival of larvae after release into the natural environment could be increased considerably by nursing them up to 3&ndash4 cm size before they leave the hatchery. Nursing can therefore be expected to have a great effect on the success of any restocking programme.

Unfortunately there is no experience on the nursing of naked carp larvae. However, the consultant believes that conventional nursing ponds could be successfully used for this species.

At the Fisheries Research Institute at Xining there is a vacant area suitable for nursing pond construction. It would be possible to connect the new ponds to the existing water supply and drainage system. It is recommended, however, that the nursing ponds should not be built in the same way as the existing deep ponds.

Though the advantages of deep ponds have been proved in the warm climatic regions of China, in the cool climate of Qinghai Province shallow ponds may be advantageous since the water can warm up better in a pond where the average water depth is only about one metre.

No drainage canal is available at low level at this site, and the water must be pumped out of the ponds. Therefore nursing ponds should not be larger than 500 m 2 in order to facilitate easy and safe harvesting. This size of pond can be conveniently harvested by fine mesh nets.

Since there is no outlet in the pond the bottom should have a slope of 0.1&ndash0.2 percent towards the inlet. In such a pond fresh water could be provided for the concentrated fish stock during harvest. The proposed slope of the earthen dikes is 1:3 in order to provide more shallow water areas around the pond dike to promote the production of feed organisms.

Pipe inlets with a diameter of 150 mm and equipped with closing devices are recommended for the nursing ponds. It is important to filter water through a fine mesh before it flows into the ponds.

2.3.4 Transporting Equipment

In the proposed system the transportation of the fertilized eggs and the nursed fry is an essential part of the operation. A four-wheel drive truck with a maximum load capacity of 2 t would be sufficient. The eggs can be transported in the special polystyrene boxes used for the transport of live salmonid eggs.

The nursed fry can be transported either in oxygen filled plastic bags or in fibreglass tanks. Since there is no experience on the transportation of nursed naked carp fry, the best way of doing this must be worked out through experiments.


Coral reef fish breeding: the secrets of each species

In recent years, the interest in the trade of tropical fish has increased significantly, with direct negative repercussions on coral reefs and marine ecosystems.

The reproduction and rearing of some of the species most commonly used in the aquarium trade actually represent an economical and ecological tool for broadening development. The present study illustrates the first case ever of a small Indo-Pacific Pomacentridae, Chrysiptera parasema, successfully reared in captivity. Eggs were obtained from spawners reared in 80-l tanks under controlled conditions. Spawning began after 3 months: the couples were formed, and eggs were laid after a brief courtship. The male normally guarded the nest and chased away the female if she entered it.

The eggs, about 300 in number, are demersal and elongate ovoidal in shape, measuring approximately 1.2–1.5 mm and coming with a large oil globule. Hatching took place at 28 °C during the first 2 h of darkness, over a total time period of 96 h. A proper diet of enriched PUFA as a first food, combined with a photoperiod of 24L/0D, proved essential for survival of the C. parasema larvae.

These results are very promising in terms of both future captive production of ornamental fish and efforts to minimize environmental impact.


Watch the video: Experiment: LAVA vs FISH Under Water! (January 2023).