BY DR. TIM LEARD

MSU National Warmwater Aquaculture Center

Most business people are concerned about factors that affect the profit margin associated with production and sale of their product. Catfish farmers are no exception, and the severity of the economic impact of disease on pond fish production is an ongoing debate. From time to time, various figures are tossed about in an attempt to quantitate this loss, however, they are little more than a rough guess. Accurate estimates of fish losses are very difficult to obtain in a pond environment, and no format exists by which farmers routinely report mortalities. This is in contrast to most modern livestock production systems where disease outbreaks are well documented and accurate counts of mortalities are easily obtained.

The problem comes from the pond environment which obscures visual observation of the fish. The farmer may observe fish at feeding time and estimate numbers based on the amount of feed consumed, but researchers debate what percent of fish eat at every feeding. When fish become sick and die they may or may not float to the surface depending on factors such as water temperature. It is difficult and time consuming to count dead fish, further complicating quantitation of disease impacts. Perhaps the most reliable information available is based on the number of fry hatched and stocked each year versus the number of food fish harvested. Industry wide it appears that one-third or less of the fry stocked make it to market, but not all succumb to disease since cannibalism, predation and water quality factors also contribute to mortality.

We might be tempted to take this information and calculate the costs associated with the loss of two-thirds of a crop, however, no one knows for sure at what stage of the grow out period that these fish died. Fry are stocked to ponds at seven to ten days of age having consumed very little feed. These fish are far less valuable than a fingerling that has been fed all summer, which in turn is much less valuable than a food size fish ready for market. Based on submissions to the fish diagnostic laboratory at Stoneville, most disease outbreaks appear to occur in fingerling ponds. If you are a fingerling producer, this could be a serious loss since fingerlings, being smaller fish, are stocked at much greater densities than food size fish. For food fish producers with a few fingerling ponds, it is preferable to lose fingerlings in which you have invested much less feed, than to lose a pond of food fish ready for market.

Fortunately, there are only a handful of major diseases recognized in channel catfish. Unfortunately, some of these are capable of causing major losses in a pond environment. Disease management in ponds is a challenging endeavor. Only two antibiotics and one parasiticide are currently approved for use in food fish. The only way to deliver an antibiotic to fish is through the feed. Sick fish tend to stop eating, thus attempts at antibiotic treatment are targeted toward stopping the spread of a disease to asymptomatic fish. In some disease outbreaks, the entire pond will stop eating and treatment is futile. Treatments are further complicated by the expense of these compounds, and the amounts required to treat the population of a 10 to 20 acre pond may not be cost effective.

The alternative is for farmers to accept disease losses as part of the cost of doing business. Relative to other aquatic species, catfish have the least value on the wholesale market. Producers must weigh the costs of land acquisition, water use and pond construction against projected income levels. The challenge comes in finding the level at which a balance is achieved between the cost of producing this species and making a reasonable profit, thus farmers may be forced to push capacity limits in order to survive in the catfish business. In summary, there are no clear cut answers regarding the economic impact of disease on the catfish industry. Fish losses will continue to be a cost of doing business. Fortunately, the incidence of disease in food size fish is relatively low and most outbreaks in these ponds are managed without medications. Catfish continues to be a wholesome commodity with much promise for future markets. DBJ

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