R. T. Lovell

An important reason forthe successful growth of the catfish industry in Alabama has been the consistent supplies and prices of feed ingredients. During the past 25 years, or since the beginning of the catfish industry in Alabama, prices for soybean meal and corn have rarely exceeded $200 and $100 a ton, respectively. This spring, however, prices for soybean meal reached $260 and corn prices averages $136 a ton. Predictions are that prices may reach record highs in 1996. Because feed typically constitutes about 60% of variable expenses, the aquaculture industry will need to adjust feeding practices to avoid waste. AAES research has identified ways to achieve that goal and thus keep fish farming operations profitable.

Overfeeding expensive feedis an obvious problem. Feed conversion ratio (pound of feed per pound of gain) on commercial farms is generally two or above, whereas feed conversion ratio in experiment ponds, where feed is dispensed and measured carefully, is 1.35 to 1.75 depending on fish size (conversion increases with fish size). AAES research indicates that high feed conversion ratios are at least partially caused by overfeeding.

Feed consumption by catfish in ponds varies daily, especially when fish are fed to near satiation, due to temperature, air pressure, water quality, disease, and other environmental changes. Therefore, if a heavy feeding regimen is used, the feeder should be well trained and have accurate and current information on each pond with regard to water quality factors, size and health of fish, and response of fish to feed allowance during previous days. Judicious attention to these factors will allow the feeder to decide how much feed to dispense in each pond with minimum waste. Underfeeding catfish in ponds favors minimizing unconsumed feed; however, this can reduce yield and allow larger or more aggressive fish to eat most of the feed.

Forcing catfish to eat also can be an economic liability. If the fish do not eat well because of disease or adverse environmental conditions, the feeder should not force them to eat. Catfish not fed several days can compensate in weight gain for the unfed days when they are put back on feed. AAES research has shown that year-two (harvest-size) channel catfish fasted for up to three weeks during summer can catch up with continuously-fed fish in another three weeks. The fasted fish will eat more, and need to, in order to catch up so the feeder should allow for this.

Restricting winter feeding can reduce feed costs. Generaly, catfish in ponds do not need to be fed during the cold months in winter. AAES studies indicate that year-two and year-one (fingerling) channel catfish not fed during the three coldest months of winter (December, January, and February) but fed generously from the first of March, weighed the same by mid-April as catfish fed continuously during winter. If fish are to be harvested before mid-April, however, they should be fed during winter to prevent weight loss.

Managing animal protein in feeds can reduce total feed costs. The most expensive ingredient in catfish feeds is fish meal. Early studies at the AAES showed that small catfish or food-size fish under a restricted feeding regimen required 6-10% fish meal in their feed. Recent studies in Alabama and at Mississippi State University have shown that good production can be obtained without animal protein in catfish feeds when the primary protein source is soybean meal and when feed allowance to the fish is not restricted. As the quality and quantity of protein in the feed decreases, the value of fish meal in the feed increases. However, under most commercial catfish feeding regimens, amounts of fish meal greater than 3-4% would be difficult to justify.

Recent studies at the AAES have shown that 26-28% amino acid-balanced protein feeds will yield the same weight gain sa the conventionally used concentration of 32% for food-size catfish fed to satiation during the growing season. However, under restricted feeding conditions, the higher protein feed yielded the greatest weight gains. These results agree with early pond feeding experiments at Auburn in which a ceiling was placed on daily feed allowance that resulted in the fish being underfed during the latter part of the growing season. Under such a feeding regimen 32-36% protein was optimum.

Today, most farmers try to feed the fish as much as they will consume all season, in which case the lower protein concentrations will be more profitable, especially if large fish (larger than seven ounces) are being fed. The lower protein feeds will result in slightly higher feed conversion ratios; however under 1994 cost and price conditions, feeding 26% protein feed was more profitable than feeding a 32% protein feed. Profitability of a lower protein catfish feed should be even greater in 1996.

Because of the interacting effects among dietary protein percentage, dietary protein quality, and daily feed allowance on weight gain by catfish, research indicated producers should be cautious about lowering these factors simultaneously. For example, protein quality is less important in a 32% protein feed than in a 28% protein feed; also, protein quality is less important when the fish are fed to satiety than when they are restricted.

Feed manufacturers should adjust the protein level to meet the requirement of the first limiting amino acid(s). Research at the AAES has shown that with channel catfish, this will usually be lysine. Therefore, if the feed is formulated to meet the lysine requirement, the other amino acids will be in sufficient or excess quantity. Traditionally, catfish feeds are formulated to contain a minimum amount of crude protein and not be deficient in any essential amino acid. This usually results in an excess of several amino acids being fed.

Conceivably, less protein could be used if attention is given to meeting the minimum requirement of the first limiting amino acid(s) instead of meeting a minimum protein requirement. This will require convincing catfish farmers that meeting amino acid requirements is more important than meeting protein requirements. High protein prices may provide incentive for feed manufacturers to use synthetic lysine in catfish feeds.

Recent studies at the AAES showed that increasing the lysine content of lysine-deficient diets with synthetic lysine was not as beneficial as increasing the lysine by substituting with soybean meal, which is high in lysine. Approximately 25% more free lysine supplement was needed as compared to protein-bound lysine (soybean meal) supplement to give maximum weight gain.

A great amount of research data has been produced in recent years with catfish on practical feed formulation and feeding strategies for catfish with emphasis on reducing cost (as opposed to increasing yield). But because catfish feed prices have been reasonable and consistent during recent years, the industry has been slow to make changes in formulations or feeding practices. The world supply of protein is expected to reach record costs in 1996. This will be strong incentive for practitioners to be especially innovative and to carefully review the research literature.

Lovell is a University Distinguished Professor of Fisheries and Allied Aquacultures.