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How to Deal with High Salinity
Steph Avi (firstname.lastname@example.org): At the moment, there is extremely high salinity in Sri Lanka, and it’s having an impact on shrimp farming.
I would like some advice from The List on combatting high salinity.
Atlantike (email@example.com): Check out this paper, White Shrimp, Penaeus Indicus, in Highly Saline Pond Waters, which appeared in World Aquaculture, the quarterly magazine of the World Aquaculture Society
Steph Avi (firstname.lastname@example.org): Hi Daniel:
• Salinity is 42-45 parts per thousand.
• All other metrics, like pH and alkalinity, are ok.
• We’re farming the giant tiger shrimp (Penaeus monodon).
• Not sure on the exchange rate per day.
• Fresh water is available, but it carries shrimp diseases, so we don’t use it.
Eric Muylder (email@example.com, http://www.crevetec.be): Hello Steph, shrimp can cope with 42-45 PPT salinities, but they don’t like the sensation of drying out, caused by an osmotic difference between their body fluids and the surrounding water. To compensate, they drink saltwater and then have to pump out the salts, a process that consumes energy—energy that could be contributing to growth. On the positive side, in high-salinity water, shrimp store water soluble amino acids (glycine, proline, arginine, glutamic acid, betaine) in their cells to increase the osmotic pressure, which makes them taste better.
In high-salinity water, you can help the shrimp by feeding them high-quality feeds with lots of protein and highly unsaturated fatty acids (HUFAs). Some anti-stress nutrients like vitamin C and astaxanthin will also help. In Iran, with salinity levels around 45-50 PPT, the introduction of special feeds made it possible to farm shrimp.
Steph Avi (firstname.lastname@example.org): Thanks, Eric! I will look into the nutrient side of it.
Tony Charles (email@example.com): Here in Australia many farms grow P. monodon at the salinities you described, but probably not for the entire growout period. Salinities are usually high early in the growout period, but they don’t cause any problems.
Martin J.M. Guerin (firstname.lastname@example.org): As mentioned by Eric, the nutritional approach is interesting. High-quality proteins with balanced amino acids supply high digestibility and palatability and help reduce the amount of nitrogen released into the environment, resulting in lower feed conversion rates (FCRs) and better protein utilization. This is important because NH3 is more toxicity at high salinities and water temperatures. Protein remains a good source of energy as long as NH3 levels are kept in check.
Among the amines listed by Eric, betaine is interesting because it is not an amino acid, therefore not deposited in the muscle, but instead remains in the hemolymph to maintain its osmolality without the harmful effects of salts.
Checking the salt content in your raw materials (fish meal, crustacean meals, squid meal) and trying to reduce it will also help reduce the osmotic stress and energy expense for osmoregulation.
High levels of HUFAs are important to the integrity of the cell membranes that are heavily challenged by the osmoregulatory activity.
You will, however, compared to lower salinities, get reduced growth at higher salinities, but your shrimp will taste better and be firmer.
As stated by others, yes, it is possible to grow monodon and vannamei at high salinities.
Nelson Gerundo (email@example.com): Hi Steph, the dry season in your country is about to end, so you can expect the Yala Monsoon to come in a few days if your farm is located anywhere on the Northeast Coast of Sri Lanka, where most major shrimp farms are situated.
Steph Avi (firstname.lastname@example.org): Thanks for all the responses!
Yes, Nelson, we have been waiting for rain for a while. Hopefully, it will come soon!
We stocked at the end of January and the beginning of February, so it looks like we will be harvesting in July. It’s my first crop, so I want to follow the best practices.
Mark Napulan (email@example.com): Hi Steph, you may encounter the following problems with high temperatures and salinities:
• Hardshell (heavy calcium carbonate precipitates)
• Dinoflagellates (naked and armored)
• Vibriosis (green colony dominance)
• Algal blooms (if your pathway is photo-autothropic).
• Luminescent bacteria (Vibrio harveyii)
Patricio Bucheli (firstname.lastname@example.org): Regarding rapid salinity drops in shrimp ponds, I’d appreciate some inputs that would explain how bacteria, specifically pathogenic bacteria, affect shrimp at high salinities? Here in Ecuador, in some areas, rain is dropping salinities from over 37 PPT to 15 PPT in 2-3 weeks.
Giovanni Chasin (email@example.com): Patricio, I suppose your pathogenic bacterium is a Vibrio. Which one? Were you routinely monitoring Vibrios? Is this bacterium also found in postlarvae shipments? Or hatcheries?
Here in northeastern Brazil (Rio Grande do Norte), at the farms under my control in Ares and Macau, Vibrios behave with different patterns even when the salinities are almost the same. When salinities dropped 15 PPT to 35 to 40 PPT at the farm in Macau, Vibrio populations dropped significantly and remained stable for a long time. At the farm in Ares, Vibrio populations were higher and more erratic with a greater impact on the shrimp.
In June 2015, we experienced high mortalities due to the presence of V. parahaemolyticus at the Macau farm. At the intake water pump station and in the canals that feed water to the ponds, the water was abnormally crystal clear, and the salinities were around 30 PPT. Even with heavy fertilization, we could not get an algae bloom. Certainly, our water chemistry was off, but we never identified the problem.
Patricio Bucheli (firstname.lastname@example.org): Hi Giovanni, good to hear from you, and thank you for your comments. Yes, I’m referring mostly to Vibrios, but other bacteria as well. My interest has to do with the direct effect of the salinity drop on the microbial communities. There’s some information on the effect of different salinity levels on Vibrios’ growth and survival, but I haven’t found any info on how salinity reduction works on bacteria.
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