Linda Benedict | 5/19/2009 12:34:04 AM
Although much genetic research involves developing ways to improve reproduction, it is just as important to develop methods to prevent reproduction. One reason is the potential for enhanced growth. Animals such as fishes invest substantial energy into reproduction that could be diverted to enhanced meat yield if they were reproductively sterile.
Sterility can be induced several ways, but most have not received much study in fish and shellfish. One method involves gamma radiation, a technique we are evaluating in the Malaysian prawn. The goal is to use sterility to improve yields and reduce size variation of cultured prawns.
Culture of freshwater prawns as a supplemental crop is rapidly gaining interest in the catfish-growing areas of the South. Barriers to profitable prawn culture include growth suppression and variation caused by social pecking orders. These pecking orders are based largely on sex, with a few large males dominating most of the population.
Studies in 1997 and 1998 indicated that it is possible to produce sterile males by gamma irradiation of juvenile prawns. Males irradiated at low doses had significantly lower numbers of sperm than did non-irradiated males. Males exposed to higher doses did not have sperm present in the testes at all. In females, the number of gravid and mated individuals decreased with higher dosages, and the number of virgin individuals increased with higher doses.
More research is needed to refine variables such as dose levels and exposure periods, but in these initial studies, it appeared that although irradiation interfered with reproduction, it did not reduce survival. Because of small sample sizes, analysis of production traits such as weight and proportion of tail meat was not possible and is being pursued.
Unlike other techniques used to reduce obstacles to growth, irradiation can be done easily and cheaply. Commercially appropriate numbers of larvae could be irradiated in batches, adding a small cost to existing hatcheries. These larvae would represent improved seedstock that could be sold at a higher price. Their sterility would guarantee that producers would return to obtain new seedstock, thus protecting the investment.
If sterility can be induced reliably, another benefit will be to reduce concern about prawn culture in states, such as Louisiana, that strictly control introduction of non-native species and genetically modified animals. Irradiation of prawns could serve as a model for applying reproductive sterility in other aquaculture species such as fish or oysters.
Personnel involved in sterility research include Ingrid Ardjosoediro, Mark Bates, John Buchanan, Carmen Paniagua-Chavez, Greg Roppolo, William Wayman and Gang Yu
Terrence R. Tiersch, Professor, and Nyanti Lee, Doctoral Candidate, both at the Aquaculture Research Station, LSU Agricultural Center, Baton Rouge, La
(This article was published in the fall 1999 issue of Louisiana Agriculture.)