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Moving Juveniles from Nursery to Growout
November 30, 2007
Herry Samudra (firstname.lastname@example.org): How does one safely transfer juvenile Penaeus vannamei from nursery ponds to growout ponds? The distance at our location is about 400 meters. We have a problem with low survivals during transfer, and the animals that do survive don’t get back on feed for over a week.
Francisco Pons Zevallos (email@example.com): I have done it over a distance of 200 meters, manually, by foot, with a total biomass of no more than 80 kilos of 0.2-gram animals. How much biomass are you transferring and how big are your animals?
Fernando Huerta (firstname.lastname@example.org): I transfer two-gram animals through a 1,200-meter, eight-inch pipe with excellent results. A few hours after the transfer, the animals are back on their feed. In one night you can transfer 6,000 kilos with just four people. You have to make sure that the pipe has a consistent slope and a constant flow of water.
Herry Samudra (email@example.com): Would you gentlemen describe your protocols before and during the transfer?
Francisco Pons Zevallos (firstname.lastname@example.org): The pipe system used by Fernando Huerta is the best system for juvenile transfer. I have seen it and wish I had the resources to do it.
Here is how I do it. Our juveniles are produced in 100-ton raceways, and it is easy to collect them with nets without stressing them. Nets should be a long and “U” shaped to give the juveniles room to swim. First we drain 40% of the water from the raceway, and then we start collecting the juveniles with the nets. We collect roughly four kilos of shrimp per pass, using two nets. We lift them out of the water for 20-30 seconds to let water run off and then weigh them. A sample of about 50 shrimp is taken aside by another person who weighs and counts them and then returns them to the raceway. This way we know how many shrimp we have per gram and can calculate the total weight transferred. Next we fill two, 25-liter buckets with 12 liters of new water, or use water directly from the raceways. We add one tablespoon of hydrogen peroxide to each bucket. The water in the bucket should contain around 20 mg/L oxygen. Then we quickly put approximately two kilos of shrimp in each bucket.
We cover the buckets with a lid, and then two men with one bucket each jog them to the pond, which takes about two minutes. The dissolved oxygen in the buckets is checked again at the ponds. It should be around 10 mg/L. The lid is removed, and the bucket is placed in the pond. Then we tip the bucket and spread the juveniles around with our hands, all the while observing their condition. We try to have no more than two degrees Celsius difference in water temperature between raceway and pond. As you can see, it’s a very simple and cheap procedure. We haven’t had any big problems with this method.
Ramon Macaraig (email@example.com): What’s the largest size shrimp that can be transferred using your method? I want to transfer two to three-gram juvenile Penaeus vannamei.
Francisco Pons Zevallos (firstname.lastname@example.org): I have only transferred animals that weighed less than a gram with the bucket technique. I don’t think it would work with larger animals.
Herry Samudra (email@example.com): What are the dimensions of your “U” shaped nets? Are they shaped like condoms?
Francisco Pons Zevallos (firstname.lastname@example.org): Yes, exactly, the “U” shaped nets are shaped like condoms. I use 3/4” PVC pipe as a frame for the net, which is made with 600-micron mesh. It is around 90cm long. When we collect the shrimp, we use two nets, side-by-side, so they cover a wider area and make it harder for the juveniles to escape. You have to drag the net fast enough so that the juveniles don’t escape, but not so fast that the juveniles are pressed against the end of the net.
Sources: 1. The Shrimp List (a mailing list for shrimp farmers, “email@example.com”). Subject: [shrimp] Safe transfer from nursery to growout pond. November 14 to 21, 2007. 2. Summarized by2. Bob Rosenberry, Shrimp News International, November 30, 2007.
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