The first comprehensive book on the use of cleaner fish in aquaculture, edited by Jim Treasurer, research manager with FAI Aquaculture, Marine Research Facility Ardtoe, has recently been published. The new volume, which addresses the main issues in the farming of cleaner fish and offers guidance on how to improve growth and survival, includes contributions from a team of over 60 experts in cleaner fish biology, culture and deployment.
Rsearchers from Egypt and Saudi Arabia found that applications of green tea were beneficial to the growth performance of Asian sea bass fingerlings.
Looking after and promoting friendly bacteria in RAS systems, rather than killing the good with the bad, could have beneficial impacts on fish health and production profitability, according to the early findings of a three-year research project run by scientists in Norway, Denmark and Germany.
A team of researchers at Nofima (The Norwegian Institute of Food, Fisheries and Aquaculture Research)'s Centre for Closed-Containment Aquaculture (CtrlAQUA) focused on skin to assess the health and welfare of salmon post-smolts.
Soy peptides (SP) can be used to enhance the immune response and survival of juvenile Japanese flounder (Paralichthys olivaceus) under heat stress, according to a recent study.

SP, a soy protein enzymatic hydrolysate, contains bioactive substances that could be utilized as an immune-stimulating feed ingredient.

“Feed companies would greatly benefit from the study, as SP may now be a new ingredient source. Fish farmers may also exploit the potential of SP for increasing the defined function of cultured fish, especially in the context of climate change,” one of the authors, Janice Ragaza, told Hatchery International.

Ragaza is an associate professor at the Department of Biology, Ateneo de Manila University in the Philippines. At the time of the study, she was still doing her doctorate studies on Fisheries Science at the Laboratory of Animal Aquatic Nutrition, Faculty of Fisheries, Kagoshima University in Japan.

In the study, diet inclusions with zero, two, five and 10% SP were fed to juvenile flounder.

“If the objective is for maximum growth, then the inclusion levels should be greater than 10% SP. If the objective is for thermotolerance, 10% SP is the optimum,” she said.

After a feeding trials, the experimental groups were subjected to heat stress to measure survival rate and heat shock protein 70s (HSP70s) in gill, liver and skin.

A significant reduction in HSP70s was observed among all groups during recovery period.

HSP70s usually show up when the organism experiences heat stress. The reduction in number over time means that the organism is reaching its equilibrium (i.e. normal, pre-stress) condition,” she said.

She compared HSP70s to cooling fans inside laptops. “Like cooling fans, HSP70s bring the fish under heat stress, e.g. increase in water temperature, to stable conditions. With more HSP70s in the tissues, the fish is therefore more stable amid the stress exposure.”

Dominated by the Pacific white shrimp (Penaeus vannamei), India's shrimp sector is growing and becoming extremely dynamic. Healthy, high quality seed is key to its success, but the increasing intensification and commercialization of shrimp aquaculture to meet demand has exacerbated disease epizootics. Reports from hatcheries of mass larvae mortalities at the Zoea-2 stage prompted Dr. T. Sathish Kumar at the Indian Council of Agricultural Research (ICAR)-Central Institute of Brackishwater Aquaculture in Chennai to investigate further.

" P. vannamei and Litopenaeus stylirostris species appear to be infected," said Dr. Kumar. "They appear normal until they cross the Zoea-1 stage. Then they suddenly stop feeding after 36 - 48 hours and systemic abnormalities are observed, such as anorexia, lethargy, empty gut, reduction in feeding and absence of faecal strands, followed by delayed moulting of up to 3-4 days and gradual, progressive mortality in 30 - 90% of the larval population."

The impacts on hatcheries are significant. Losses from Zoea-2 syndrome in an Indian commercial hatchery with a stocking capacity of 100 million nauplii are estimated at around $18 - 61,000 USD. Establishing strict management practices, reducing the number of days of stocking nauplii to less than 3 - 4 days in the same unit, disinfecting everything including implements and air pipes, creating shutdown periods between larval production cycles, and physically separating units for maturation, spawning and larval rearing could all help reduce mortalities.

"My work reinforces the adoption and implementation of best management practices in hatcheries," said Dr. Kumar. "It has shown that Zoea-2 syndrome isn't caused by known infectious agents. Other pre-disposing factors could be a lack of separate larval rearing units, and shrimp hatcheries must invest in improved biosecurity to prevent losses and sustained continued larval production."

Dr. Kumar suggests that an integrative multidimensional investigation, involving physiological factors within zoea and microbial dynamics in hatcheries may help to understand the causes of digestive system impairment in shrimp and the role of opportunistic pathogens.

One hundred and 200-gram salmon smolt grew more quickly when put into seawater for grow-out compared to 600-gram fish.

This was part of the results of a study conducted by researchers from the Norwegian Institute of Food, Fisheries and Aquaculture Research (Nofima) which compared performance in terms of growth, survival, health, maturation of salmon produced by using different production protocols in RAS.

“We do not know the reason for the reduced growth during summer in the fish transferred at 600 grams. The trend was the same in all 600 grams-transferred fish, irrespective of photoperiod or salinity in RAS. We are, at the moment, doing analysis of fish composition to see if we can find an explanation,” Nofima scientist Trine Ytrestøyl told Hatchery International.

Cost implications

Ytrestøyl presented the study at the Aquaculture Innovation Workshop (AIW) 2017 in November in Vancouver. “Since the presentation at AIW, we have done the final sampling, and the 600-gram fish grew very well during the final two months in the sea from September to end of November. But despite their catch-up growth, they were still smaller than the 100 and 200 grams- transferred fish at slaughter in late November,” she said.

Cost implications are not covered by the project, she said, because it is very dependent on the sea lice situation. “If this is taken into account, it may be more economical to use the larger post-smolt of 600 grams even if it grows a little slower in the seawater phase,” she said.

The larger fish, she explained, can reduce grow-out time in open sea cage by 2.5 months, which saves one to two delousing operations, compared to stocking with 100- and 200-gram fish.

There are also health benefits, she added, because delousing is tough on the fish and leads both to reduced growth and some mortality.

It is a common procedure these days to produce salmon smolt to a bigger size before they are put in seawater for grow-out.

Seawater tolerant salmon

“Some believe that a larger size makes the fish better able to cope with sweater because they have a smaller surface/volume ratio compared to smaller fish. Thus it should be less energy-demanding for them to regulate their ion levels in seawater. In seawater, water has a higher osmolarity than the fish, so ions will diffuse into the fish, which has to spend energy to get rid of ions to keep its osmotic balance,” she said.

The traditional way produces 70- to 100-gram smolts. There has been an increase in smolt size up to 200 to 500 grams because it cuts production time in open sea cages, a procedure seen as critical in avoiding problems with salmon lice and other diseases.

“We wanted to test if it was possible to produce a seawater-tolerant salmon without using a winter signal with short day for six weeks, and also how larger fish (600 grams) would perform compared to smaller fish (200 grams) at transfer. We used brackish water at 12 ppt in some treatments in RAS to see if this would improve growth and seawater tolerance and performance after seawater transfer,” she said of the study.

Natural way

In nature, Atlantic salmon go through a smoltification process to prepare them for life in seawater and this physiological change is induced by the dark winter.

In aquaculture, however, smoltification has been induced by giving the small salmon juveniles, called parr, a period of short days of six weeks with-12 hour light and 12-hour darkness, followed by a minimum period of four weeks with 24-hour daylight.

“This is sufficient to trigger the transformation from a freshwater adapted parr to a seawater adapted smolt,” she said.

“In RAS, growers want to have optimal growth, and be able to feed the fish 24 hour, so they would like to produce a fish that can go to seawater without having a period with 12:12 light/darkness; the salmon is not fed in darkness.”

Norwegian research has shown that some salmon families have higher levels of healthy fatty acids in their muscle tissue than others.

From cancer prevention to promoting infant health and development and inhibiting cardio vascular disease, essential Omega 3 fatty acids have proven to be nutrient behemoths in human health, and researchers in Norway believe they can raise salmon bred to be teaming with the essential fatty acids.

However, over the last decade the level of these fatty acids in farmed salmon fillets has decreased owing to the substitution of fish oil with vegetable oil in the fish feed. Fortunately, salmon have the capacity to convert fatty acids from plants into EPA and DHA, according to researchers at Norwegian breeding and genetics giant Nofima AS.

While feed is the largest factor determining the level of EPA and DHA in the fillet, there is evidence that genetics also plays a role. Previous research has shown that some salmon families have higher levels of the healthy fatty acids in their muscle tissue than others, suggesting there is potential in using selective breeding as a tool to increase levels of omega-3 in Atlantic salmon muscle.

“Our research has shown that the individual omega-3 fatty acids have different heritability, as well as different correlations to other important production traits,” said Siri Storteig Horn, a PhD researcher at Nofima conducting the research. “All the major fatty acids in the muscle showed a certain degree of heritability. DHA was the omega-3 fatty acid with the highest heritability (0.26), proving to be the best trait for selection. EPA had a low heritability (0.09).”

Horn said that they’ve estimated the heritability of individual omega-3 fatty acids and their relationships to lipid deposition traits and other traits of the breeding goals (carcass, quality and disease).

“This is key to predicting the consequences of selection for higher levels of healthy omega-3, and is important information for breeders if they want to implement selection for this trait,” she added.

Gene identity

Currently Horn is working on identifying the genes associated with increased omega-3 content in salmon muscle.

“This will increase the understanding of the biological processes underlying the trait, as well as improve selection accuracy by allowing marker-based selection,” she said.

Should this prove viable, salmon breeders can implement marker-based selection for healthy omega-3 and produce a salmon with higher nutritional value to consumers.

Ultimately, Nofima wants to see if it is possible to increase the salmon’s natural capacity to convert short-chained omega-3 form plant oil into EPA and DHA through selective breeding, and in this way stop the decline in omega-3 levels in farmed salmon fillets.

To achieve this, they’re aiming at increasing the understanding of which biological processes are determining the level of healthy omega-3 fatty acids in salmon muscle.

Horn said breeding and genetics is at the very foundation of successful salmon farming and will continue to meet future challenges facing the industry.

Already a gourmet staple in Portugal and Spain, where wild-caught soft-necked gooseneck barnacles fetch up to $90 a pound, interest in culturing this novel species has begun to grow on the west coast of North America.

Based on the high demand and profit of this fishery overseas and rumblings of interest in North America as well, a professor at the University of Oregon, Dr. Alan Shanks, decided to investigate the feasibility of a commercial U.S. market and what that might look like for the Oregon coast.

As a relatively new species of interest, state regulations are still evolving. Currently Oregon regulations limit wild harvest of the barnacles to 50 individuals of any size on man-made structures like rock jetties. Nearby Washington state limits recreational harvest to a daily limit of 10 pounds whole or 5 pounds barnacle stalks.

Preliminary investigation

The investigation is a forward-thinking project by Shanks and a handful of research assistants at the University. They have three main goals:

• First: take an estimate of current inventory of harvestable-sized Pollicipes polymerus, the species found in the intertidal zone on America’s west coast.

• Second, explore possible mariculture development for onshore commercial production.

• And thirdly, work with local seafood collectives, the public and state resource managers to build a partnership for a sustainable market.

The project strives for multistakeholder collaboration to help protect and manage this growing market and avoid depleting the stocks by overfishing, which has already happened in Spain.

There are some obvious hurdles to overcome for this market to be successful, like convincing a timid American seafood palate to try something new, especially when the “new” is an oddly shaped, rubbery crustacean found clinging to rocks in the crashing surf of the intertidal zone. “We like to use the name “percebes” (Spanish for barnacle) or “devil’s fingers”…. it sounds more exotic and palatable than “barnacle”, explains Dr. Alan Shanks.

Also the current stocks of harvestable-sized adults pose a limitation to large-scale harvest in Oregon. Alan’s research assistants found only a small amount (2.3%) of the jetty populations to be of commercial interest and depending on fishing pressures could be wiped out within a year. Because of their slow growth rate, unique recruitment of larvae, and collectors having to take the whole clump of barnacles which include many tiny individuals, it could a long time to recover the stocks in those areas.

The mariculture alternative

Mariculture of these prized crustaceans seems like a good alternative to wild harvest, but has proven elusive so far.

Alexa Romersa, a grad student working on the aquaculture end of the project at the University of Oregon understands the obstacles well …. Rearing the barnacle larvae in a lab setting is notoriously difficult and you often end up with varying quality of the juvenile cohort. Larval rearing also lengthens the process because transition from nauplius to cyprid to juvenile can take between 40 and 60 days.”

It was also thought that the developing barnacles needed high water flow (which can be costly to provide) to mimic crashing waves of its environment in order to feed.

But an interesting observation in a fish aquarium at the Oregon Institute of Marine Biology (OIMB) lead Dr. Shanks to make an important discovery for the barnacle’s future in mariculture:

“I saw a cluster of gooseneck barnacles attached to the wall of the aquarium, directly above the air bubbler. There was no high-water flow in this area of the tank….yet it appeared the barnacles were thriving near the air bubbles.”

His observation led to the design of a low-flow, aerated mariculture design used in his lab set-up, along with other improvements for efficiency.

Alexa detailed the experimental aquaculture set-up in her lab:

“We work exclusively with wild caught adults and juveniles that I harvest off rocks in the intertidal. Individuals are glued onto a vertical rod placed inside a PVC tubing tank. Each tank has a water and air inflow near the base and air is connected to a coil of diffuser tubing that provides constant aeration for the barnacles.”

“The aeration tubing (the type commonly used in gardening) is the major discovery of this phase of the experiment. Previous efforts at studying growth in gooseneck barnacles in the lab have attempted to mimic natural intertidal conditions by providing high volume water flow in order to trigger the specialized feeding behavior of pollicipes polymerus. However, I have been able to prompt the same behavior with air bubbles helped along by gravity. Air is cheaper and more easily scaled to a commercial operation.”

Shank’s team has also found that they can stimulate good natural recruitment of larvae in the lab by piping in unfiltered, natural seawater containing barnacle cyprid (active swimming larvae) that then settle on existing adults and increase their stock numbers.

Diet and yield

The barnacles have been fed two diets: rotifers, a zooplankton that is bio-enhanced with micronutrients and vitamins, and an emulsified fish blend collected from the local fish processing plant. The viscera is dehydrated, then ground into a powder and re-suspended in solution for easy feeding.

The research team received a “Seed” grant from Oregon Sea Grant to cover start-up cost of the operation (building the aquaculture set-up, buying and feeding rotifers, etc). 

In terms of cost, Alexa estimates the entire operation cost about $1000 dollars to set up. The research lab is small by aquaculture standards- using about 200 gallons of seawater per day and 20psi for air. But she expects a similar sized commercial operation could successfully culture between 1000 and 2000 barnacles that would grow from juvenile to commercial size in less than a year with feeding twice daily, even faster if fed continuously.

In terms of yield she estimates that a single large barnacle would weigh in at 5g, so 200 barnacles would fetch around $160-$180 US dollars with current prices, so there is a good return on investment.

The barnacle’s unique form of recruitment with larvae preferring to settle on other adult gooseneck barnacles also makes this species ideal for aquaculture since wild harvesting takes the whole colony of barnacles at once, not just adults, and would deplenish future juvenile populations quickly.

Convincing the American market

So with many of the hurdles of mariculture being addressed, that just leaves convincing the average US consumer to take the plunge. Currently the Port Orford Ocean Resources Team is interested in selling the barnacles in their farmers’ basket, similar to the concept of Community Supported Agriculture (CSA) farm boxes.

“We don’t yet know all the nutritional facts for this tasty little creature”, says Shanks, but with the growing interest and profit potential, he is eager to look at that next. He’s working on acquiring a third research grant from Sea Grant, called the “Leaf” grant, to examine the fatty acid content of this salty little snack.

Two herbal bio-extracts, known to enhance the immunity system of humans, have been found to have the same effect on Nile tilapia fingerlings.
The European Percid Fish Culture (EPFC) group is a thematic working group within the European Aquaculture Society (EAS) that has, for the first time, organized a hands-on workshop focusing on the out-of-season reproduction of pikeperch (Sander lucioperca).
Lobster larvae and turbot juveniles exposed to direct application of ozone exhibited higher survival rate, reiterating the benefits of the treatment.
The National Oceanic and Atmospheric Administration (NOAA) has awarded scientists at Oregon State University two aquaculture grants, one that will help hatcheries feed certain marine fish more efficiently and the other intended to make oysters safer to eat.
Soy peptides (SP) can be used to enhance the immune response and survival of juvenile Japanese flounder (Paralichthys olivaceus) under heat stress, according to a recent study.
University of Maine assistant professor of marine biology and aquaculture Dr Heather Hamlin has been studying why the survival rate of salmon eggs in hatcheries has declined by as much as 50% in the last 18 years. And now Hamlin and Ph.D. candidate LeeAnne Thayer may have gone some distance to solving the problem.

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