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Hatchery Mortalities—A Discussion from The Shrimp List
Laurent Queffelec (firstname.lastname@example.org): We have been breeding blue shrimp (Penaeus stylirostris) for 15 years with good results. This year, however, we have been faced with an unknown problem that has caused huge mortalities in our last three hatchery production cycles. Symptoms are always the same: larvae develop normally from nauplii to the mysis-2 stage and then “freeze”. They have twisted antennas, stop eating, swim upside down and their pleopods beat uncontrollably and rapidly. Their digestive tracts are empty and their hepatopancreses abnormal. Survival for last production cycle was 3% at PL-18, and when those PLs were stocked in growout ponds, their survival was only 50%, demonstrating their overall weakness.
A sample was sent to Dr. Lightner’s lab at the University of Arizona in the United States, and it came back negative for all known diseases—including early mortality syndrome (EMS/AHPND). We suspect chemical poisoning, but we have little information concerning lethal chemical levels for blue shrimp.
If any of you have ever seen similar symptoms, I would like to here from you, even if you are not working with blue shrimp.
Juan Aguirre (email@example.com): What’s the source of your water? Tell us more about your filters and your water treatment and conditioning protocols. What feeds are you using? Is there anything unusual about your algae culture?
Laurent Queffelec (firstname.lastname@example.org): Juan, we are using seawater from a lagoon with salinity varying from 36 to 40g/l, depending on the amount of rainfall.
Our hatchery water is treated with EDTA, sand filtered, passed through a mesh filter at 1 µm and then through a charcoal filter. We tried two different manufacturers of EDTA and even changed the sand in the sand filter between the first and second bad cycles. Oxytetracycline (OTC) is used as a prophylaxis. Our successful protocols have not changed for years, except for the addition of a UV treatment after the second event.
Our algae culture tanks are outside the hatchery, and we feed Artemia and microparticles. All our practices have been unchanged for years.
At the beginning of production our water is free of Vibrios, however, they increase over time, but no pathogen has been identified as predominant.
We have tried several different strategies:
• Tanks with UV-treated water and others with ozone and UV-treated water did not correct the problem.
• Tanks maintained without Artemia or phytoplankton, to prevent contamination, did not correct the problem. The larvae died before reaching the critical mysis-2 stage.
• Tanks treated with oxytetracycline or erythromycin from day one did not correct the problem, although we did notice a higher bacterial load with the erythromycin treatment.
We are located in a rural area that is developing quickly. A mining industry and a growing population affect our water quality. During the last three years, for the first time ever, one broodstock tank out of six had mortalities over 90% each year. That never happened before. We also saw dead crabs in those tanks. Analysis of shrimp showed the presence of pathogenic Vibrios, but we don’t know it if they were causal or opportunistic. We also have more mortality during transfer and eyestalk ablation than ever before and lower numbers of nauplii per female. Again, our protocols for broodstock maintenance, feeding and maturation have not changed in years.
Our next production cycle will begin within a month. We’re going to try and send some of our nauplii to a different hatchery to see if they develop better elsewhere. We will also try to get nauplii from a different hatchery to see how they perform in our hatchery.
Comments still welcome!
Hank Bauman (email@example.com): Could you extend your pipeline farther out into your lagoon? Your salinity is high, and as you mentioned, your incoming water could be getting more and more polluted.
I would get clean seawater and nauplii from another hatchery and run side-by-side bioassays in your hatchery. Grow the algae you’re going to feed in your hatchery in the other hatchery’s clean water.
Right now, I would bet your water is bad. How long have you been discharging into the lagoon? How big and deep is the lagoon, and how much water does it exchange with the ocean every day?
Good luck, dead larvae are no fun.
D.V.S.N. Raju (firstname.lastname@example.org): Laurent, because Dr. Lightener’s lab has not found any known pathogen in your larvae, I’m thinking your problem could be poor broodstock quality, particularly the health and nutritional status of the females. Try conditioning your males and females separately for 15 to 20 days in high-quality, finely filtered, EDTA-treated water. Feed them high-quality fresh feeds, like live polychaetes, frozen squid, oyster meat and maturation pellets supplemented with astaxanthin pigment. Maintain the males in 26ºC water and the females in 29ºC water. If you don’t have a good recirculating system, do a slow (so you don’t stress the broodstock) 150% water exchange every day.
Hank Bauman (email@example.com): Laurent, the fact that your lagoon’s salinity is above 35 and up to 40 ppt suggests almost stagnant water with evaporation and little exchange with the ocean or no influx from rivers or streams.
Laurent Queffelec (firstname.lastname@example.org): Thank you, Hank and Dr. Raju.
Dr. Raju, we already have maturation protocols in place that include temperature controls, simulation of night and day and high quality food that have been working very well for ten plus years, but recently nauplii production per female decreased, although the hatching rate remained normal, indicating a problem with fecundation. We have not yet determined if the problem comes from males, females, or both. But we suppose it is also linked to the hatchery mortalities.
Hank, you’re right, the water exchange between open sea and the lagoon is limited, leading to high salinities and maybe the accumulation of pollutants. We have three rivers that mitigate salinity, but it’s been very dry for two to three years. We have rare but strong rains, and I fear the rainy periods bring loads of pollutants from agriculture, mining and urbanization into our lagoon.
A complete testing for heavy metals in the lagoon and in the hatchery waters is scheduled for next week, I’ll keep you posted on the results.
D.V.S.N. Raju (email@example.com): Lauren, I’m guessing that the problem with fecundity is directly related to the nutritional status of the female broodstock. Try changing your feeding protocols. Make sure that your fresh feeds include squid, oyster meat, live polychaetes, white/yellow clam meat and maturation pellets supplemented with vitamin E and A, astaxanthin and paprika. Add two parts per million of vitamin C directly to your broodstock holding tanks twice a day. Make sure your salinity does not drop.
Since the mortalities are happening mid-way in the larval cycle (mysis stage), your problem is definitely not due to water quality. If it were water quality, the problem would occur earlier, probably during the zoea stage. You need a thorough water quality analysis as soon as possible, and you should not rely on a single source of sea water. Try to install two or three pumping points in your lagoon. If you are facing a problem with one, you can switch to the other. Most of the shrimp hatcheries in India have multiple water intakes because we face seasonal problems with water quality here.
Try filtering your water slowly through a series of sand beds that reduce turbidity and heavy metals.
John Birkett (firstname.lastname@example.org): Laurent, my best guess is that your problems starts with an ionic imbalance in your water that gets worst after a few days of culture. Test your bicarbonate counts and total alkalinity. Keep your pH below or at 8 with CO2—and pray for rain.
We sometimes get molting problems during the mysis stage, but if your fecundity rates are low watch for ionic balances and try giving the spawning and hatching tanks the same water treatment that you give to your larval rearing tanks. Put fresh water with algae in them and try some sodium bicarbonate in your water if you find your bicarbonate counts are low. Keep in mind that bacteria and algae in a still-water lagoon can eat away quite a bit of your free ions and also accumulate the nasty ones like heavy metals and toxins.
Hank Bauman (email@example.com): Dr. Raju, it seems logical that water parameters, such as salinity, could cause mortality at the zoea stage, and until recently I would have agreed with that. But at our site, due to weather conditions this year, our salinity dropped to 24-26 ppt for about a month and a half. Strangely, our zoea stages went through with no obvious signs of stress or even slow growth at those low salinities. But when they metamorphosed to mysis stage, they grew slowly, had very thin muscle development, semi-empty guts and survivals dropped from our normal 90%, or so, at that stage to about 20% by PL-2.
Recently our salinity came back up to 28-30 ppt and as of now we have tanks running at 80 to 85% survival at the early PL stage. Salinity was the only variable that changed.
I don’t mean to imply that all water parameter problems won’t result in mortalities until the mysis stage. I have seen massive zoea mortality due to water problems.
Laurent Queffelec (firstname.lastname@example.org): Thank you again for all your advice and for sharing your knowledge and experience.
We have come to the point where we will need a consultant to solve this problem. Our next production is scheduled to begin within a month. We have clues that problem must be bacterial, maybe initiated by chemical stress.
So please feel free to send me (off-list if you prefer) your offers for an on-site consultation for two weeks (about) beginning early January 2014 in New Caledonia. French speaking consultants are preferred, but we can handle English and Spanish. Rebuilding the hatchery must be forgotten, we need to find a quicker solution.
Laurent Queffelec (email@example.com): We have finally received the analysis of our water:
Juan Aguirre (firstname.lastname@example.org): Laurent, this paper on heavy metals might be helpful:
Laurent Queffelec (email@example.com): Thanks for your contribution, Juan. It appears our figures for copper are very high. Does anyone know the toxicity levels of copper for penaeids? Selenium and zinc appear high, too.
I found a publication concerning selenium’s toxicity to fish. Fish kept in water with two ppm selenium did well for 8 days, but then they stopped feeding and showed abnormal behavior. Death occurred for all the fish between day 18 and day 46. Could this be what’s happening to our shrimp at the mysis-2 stage?
Dallas Weaver (firstname.lastname@example.org): Selenium is a required nutrient, which makes it tricky. It causes developmental deformities in other animals (birds) and is concentrated by some algae/plant species, which, when eaten, move it up the food chain. In the United States, it is this bio-magnification that has resulted in limits of 50µg/l for selenium in drinking water and 5µ/l for environmental waste discharges into river systems.
Have you changed your source for activated carbon in your filters? Its effectiveness depends very much on the type and source.
I would add EDTA after you analyzed your water quality because it can distort some heavy metal measurements.
Alain Michel (email@example.com): Laurent, I have followed the discussion about the mortality problem you are encountering. I was involved with the development of P. stylirostris hatcheries in New Caledonia in the 1970s and 1980s, and problems like yours occurred frequently. When you are questioning everything, the best think to do is return to the basics. There are three components in your culture system in constant interaction: the quality of the pumped water and its evolution through the hatchery cycle, the different parts of your system (pumps and filters) and the different stages of the larvae. Observation of your larvae and their behavior is important because they are constantly experiencing all the system’s stress factors. Stress is generated by water quality and its variations, the quality of the spawn, quality of your algae and Artemia and so on. To complicate things you have the evolution of your larval ecosystem, which can turn bad or stay stable. For me the best criterion for trying to determine the cause of a hatchery problem is to look at the larvae.
• If the hatching rate is good and the larvae are metamorphosing to zoea-1 and feeding aggressively, I think that the quality of the broodstock is probably okay. If this were not the case, their nutritional reserves would be too low, and they would fail to feed properly at zoea-1.
• Clearly nauplii are the most sensitive to pollutants. If they are molting well at zoea-1 with normal devaginated setae, water quality at that stage should be okay.
• If the larvae are feeding on unicellular algae and molting from zoea-1 to mysis-1, your algae must be okay. If you have an algae crash that creates foam on the surface of your tanks, it could be releasing toxic by products.
• In your case, the problem starts at mysis-2, so you can suspect that the introduction of Artemia may be modifying the bacterial balance in your tanks in favor of Vibrio populations that release some toxins. It’s a classic hatchery problem. Have you tried the old remedy of adding some sugar to your water to increase the populations of bacteria. It’s always good to have a diverse bacterial population. Are you using decapsulated Artemia cysts? Some hatcheries in New Caledonia don’t use any algae during the zoea stages, which has the advantage of eliminating one source of know detrimental variations. You can do that by using a floc system in the larval tanks, created by heavy aeration and a microparticulated feed. What you describe looks to be an imbalance in your larval tanks at the mysis stage, so it could be useful to modifying the balance drastically to see what happens. Often the problem disappears as suddenly as it appeared and you never know why. I hope this will be the case for you. I understand your frustration when the protocols that you worked with for years no longer work.
By the way, your water quality analyses are showing that the EDTA is working. I am not sure that the level of copper is toxic. If it is toxic, it would affect nauplii first. I think you should look at the bacterial balance first. Have you looked for luminescent bacteria (Vibrio harveyi) in the tanks at night?
John Birkett (firstname.lastname@example.org): Alain, I agree with your observation: if the zoea metamorphose to mysis stage without a problem, the heavy metals or ionic balance isn’t playing a major role in the mysis problem. Most problems that start at the mysis stage are bacteria related, caused by an imbalance due to an algae crash, lack of algae culture (for water quality more than nutrition), Artemia feeding related problems (toxins, disinfectants residuals, bacteria) and bacterial problems with the incoming water. Normally, at the mysis stage, we continue to raise tank levels with chlorinated water and cultured algae, feeding mostly liquid diets and Artemia. Even then a tank may get out of balance and a mysis to early PL molting problem will appear. The animals will stop feeding and basically you have to change the whole tank media to stop mortality.
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