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January 19, 2016


Eric De Muylder’s Comments on the Quality of Postlarvae


Currently, on The Shrimp List, a mailing list for shrimp farmers, a discussion is taking place on the quality of postlarvae (PL).  In one of the most recent postings to the discussion, Eric De Muylder, an indoor shrimp farmer in Belgium and a shrimp feed consultant, says:


If PL quality is not of good, what are the consequences?


The PLs that I get from Shrimp Improvement Systems in Florida are not only small, but also very uneven in size.  I can’t imagine a rougher stress test than being on a plane for 24 hours in a small bag at 20 to 16°C.  I don’t observe a lot of mortality, even after acclimatization.  When they arrive, the maximum mortality is 20%, but it’s usually around 10%.


But then, after 2-3 weeks, there is huge difference in size.  Some shrimp are half a gram or even one gram while others are still smaller than 1 cm.  Even after 4-5 weeks, I have some four-gram shrimp and others are still 1 cm.  Surprisingly, the guts of the small shrimp are full, so it is not that they are not eating.  They simply don’t grow.  I usually feed the PL-11s Artemia for five days, but for recent batches, I increased it to ten days because they were so small.  All this is to favor the growth of the small ones.


Initially, when I started my farm, I made the usual mistakes and was faced with water quality problems during starting up, like nitrite peaks.  So I accepted low survival as my own mistake and part of the learning experience.  But then, I had subsequent batches of shrimp where nothing went wrong, no mortalities or water quality problems at all.  But still, I got low survivals, so I figured out a system to count my biomass and came to the horrible conclusion that I lost 60% of the PLs in the nursery before they reached one gram and another 20% as they grew from one gram to five grams.  The  80% mortality corresponds with the 80% that were under 9 mm on arrival.  Once they pass five grams, my mortality rate is almost zero.


I have made changes at my farm that increased survivals, but I still have the same number of small shrimp, so I don’t know if it is really worth the effort to “save” the small shrimp, if they are not going to grow.


I have spoken with other farmers in Europe that use different systems, and they, more of less, have had the same experience.  Basically, whatever you do, there is only a small proportion of shrimp that grow to harvest size.


My questions to The List are:


• How do I correlate the quality of the PLs that arrive with the proportion that will grow to harvest size?

• What causes the PLs to stay small?  Is it incomplete development during larval rearing?

• Is it genetics?  Epigenetics?  I assume the PLs are genetically similar and come from the same batch because I only buy 50,000 to 70 000 PLs at a time.


You can tune in to the entire discussion at The Shrimp List!


Source: The Shrimp List (a mailing list for shrimp farmers).  Quality of PL11 and Subsequent Growth.  January 19, 2016.

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