Fig. 1. Benthic clumping behavior of Atlantic sturgeon larvae. brine shrimp to first-feeding larvae was the only effective way to achieve acceptable survival and growth for about the first 30 days of rearing. Larval Atlantic sturgeon rejected formulated feed. Therefore, to obtain desired results with the sturgeon, sufficient amounts of their preferred first food, brine shrimp, must be supplied to culture tanks on a continuous basis. This was achieved by using timer-activated bellows-type pumps to deliver live brine shrimp from supply tanks directly into the inflowing culture water supply lines. Typically, our pumps were set to activate for three minutes every half hour for about 30 days or until the conversion threshold size (CTS) of fry was attained. Experimentation showed that when fry reached the CTS (average length = 34.5 mm and average weight = 0.18 g), they could be converted immediately to a formulated diet with less than 25 percent mortality. Conclusion and Recom�endation In rearing first-feeding Atlantic sturgeon fry, large quantities of brine shrimp are required because a hatch of over 150,000 larvae from one female sturgeon is not uncommon. Producing and feeding brine shrimp to that many fry is labor intensive, but must continue until CTS is achieved. In one documented experiment, we used 9 kg of brine shrimp cysts 56 MARCH 2007 Fig. 2. Atlantic sturgeon larva with yolk sac. over nearly 30 days to rear only 20,000 larvae. First-feeding Atlantic sturgeon show greater survival and faster growth when reared at low densities. Inasmuch as first-feeders are substrate oriented, it is important to have enough tank substrate area to accommodate them. We found that the CTS can be attained in 26 days when tank densities are initially about one larva/3 cm2 of tank bottom. This translates to about 500 larvae per 0.6 m diameter tank. Our studies showed that increasing the initial rearing density of larvae beyond that level creates undesirable competition for space and feed which, in turn, can cause hygiene problems. Simply stated, whenever the larvae are too crowded and not kept free of waste feed and fecal material, the scale can be tipped in favor of parasites, such as Chilodenella sp. , Trichodina sp. , Hexamita sp. , Icthyoboda sp. , and Icthyopthirius multifiliis (Ich). If these parasites are not eliminated, conditions deteriorate For example, one of our studies resulted in 50 percent mortality in one parasite infested tank over a four day period. If diagnosed early, adjustment of environmental conditions and treatment with Paracide F (formalin) per label instructions will help. In summary, for fry culture of Atlantic sturgeon, I recommend having enough space, an ample supply of brine shrimp and keeping tanks clean. In other words, good husbandry practices are essential. Among other lessons learned are that tank culture of five year classes of Atlantic sturgeon cultured, labor and space during larval rearing are at a premium. Therefore, an alternative rearing strategy was briefly tested at NEFC wherein about 70,000 early feeding fry, initially reared at above-optimum density, were placed in a fertilized pond where natural food was available. The technique showed promise when, after two months, about 5,000 healthy fingerlings were harvested. When the opportunity once again arises, we hope to improve upon the pond rearing technique for this species. Notes 1 U.S. Fish & Wildlife Service, Northeast Fishery Center, Lamar, Pennsylvania USA. References Mohler, J.W 2004. Culture manual for the Atlantic sturgeon Acipenser oxyrinchus oxyrinchus. U.S. Fish & Wildlife Service. Hadley, Massachusetts. USA. Williot,P., L.Sabeau, J.Gessner, G.Arlati, P.Bronzi, T.Gulyas and P.Berni. 2001. Sturgeon farming in Western Europe: recent developments and perspectives. Aquaculture of Living Resources 14:367-374.
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