Preface

Introduction

Feed cost is the major variable operating cost associated with channel catfish production, and commercial feeds contain a liberal amount of expensive, high-quality protein. Channel catfish can assimilate relatively high levels of dietary protein; feeds used for catfish grow out have traditionally contained up to 35% dietary protein. Consequently, considerable research effort has been expended to determine the quantity and quality of dietary protein necessary to achieve optimum performance of catfish. 

The optimum level and quality of dietary protein to include in commercial catfish diets are dependent on several factors, including the balance between energy and protein in the diet, the amino acid composition of the diet, and feeding rate. Protein is needed to promote catfish growth, while less expensive feed ingredients like corn and wheat are sufficient for providing energy. The problem is that catfish readily use expensive dietary protein as an energy source as well. Catfish diets should be balanced to ensure that adequate levels of protein and the less-expensive energy sources are supplied in proper proportions to minimize the use of protein for energy and to maximize protein deposition. 

The quality of protein sources used in catfish feeds must be taken into account to ensure that amino acid requirements are met. Protein quality is dictated primarily by the concentrations and bioavailability of indispensable amino acids in the protein. Indispensable amino acids are nutrients that are not synthesized in the body and must be supplied in the diet. Proteins of animal origin, particularly fish meals prepared from whole fish, are considered nutritionally superior to proteins of plant origin. Animal proteins generally contain a higher level of indispensable amino acids and are more highly digestible by catfish than plant proteins. Commercial catfish feeds have typically contained relatively high levels of protein supplied in part by animal protein supplements. However, there is a growing body of evidence that dietary protein levels can be reduced and that animal protein can be reduced or eliminated in feeds for food-size catfish. 

Feeding rate may also affect the optimum dietary protein level. Fish fed at a restricted rate may require more or higher-quality protein, particularly if feeding is severely restricted. In practice, though feeding rates may vary considerably, most commercial catfish producers generally do not restrict feed below 80 pounds to 120 pounds per acre per day. Recommendation on the quantity and quality of protein needed in catfish diets given in this bulletin are suitable for producers feeding in  this bulletin are suitable for producers feeding in this range. This publication summarizes various studies conducted at the National Warmwater Aquaculture Center in Stoneville on the protein nutrition of channel catfish grown from fingerlings to marketable-size catfish.

Protein Requirement Studies

Protein Quantity

Since all previous research on dietary protein level had been conducted with fish fed to satiation, Experiment 5 was conducted to evaluate dietary protein level and feeding rate. Catfish were fed either a 24%, 28%, or 32% protein diet to satiation or at a restricted rate not to exceed 120 pounds per acre per day. 

There were no differences in weight gain or feed conversion ratio regardless of feeding rate or dietary protein level (Table 8). Fish fed the 24% protein diet were fattier and had a reduced carcass dressout (Table 9). Feeding rate did not affect fattiness or dressout. 

Upon examination of feed consumption data, it was apparent that there were no differences in the amount of feed consumed between fish on the two treatments. That is, fish fed to satiation consumed the same amount of feed as those receiving the restricted ration. These data show that although fish convert feed and grow equally well on a 24% protein diet, their dressed yield was reduced as compared with the other two diets. Based on these data, we concluded that feeding a 28% protein feed to fish fed no more than 120 pounds per acre per day provides an adequate amount of protein. Also, it appeared that the fish were satiated at this level of feeding.

Experiment 6 

Since there were no differences in fish fed to satiation or at a restricted rate in Experiment 5, Experiment 6 was conducted to compare a 28% and a 32% protein diet in which feed was more severely restricted. Fish either were fed once daily to satiation or were restricted to no more than 80, 100, or 120 pounds per acre per day. 

There were no significant differences in weight gain and feed conversion among fish fed the 28% or 32% protein diet when compared at each feeding level (Table 10). As the feeding rate increased, feed consumption and weight gain generally increased. The exception to this trend was that feed consumption and weight gain were the same whether fish were restricted to 120 pounds of feed or fed to satiation. Apparently, this level of feeding was enough to satiate the fish. These results were similar to those from Experiment 5. Feed conversion ratio was unaffected by feeding rate. 

Fish fed the 28% protein diet had a lower carcass dressout than those fed the 32% protein feed (Table 11). This response has not been consistent in our studies. In fact, there are generally no differences in carcass dressout between fish fed 28% or 32% protein diets. Concentration of dietary protein did not affect fillet fat of fish, but feeding rate did affect body fattiness. Visceral fat increased as feeding rate increased. Fillet fat increased in fish fed more than 80 pounds per acre per day. However, fillet fat content was the same in fish fed to satiation and fish fed 100 or 120 pounds per acre per day. 

These results helped to refine our knowledge of protein requirements in the channel catfish further. It appears that 28% protein is adequate for catfish growth even when feed is restricted to 80 pounds per acre per day.

Experiment 7 

All experiments conducted thus far supported the contention that a 28% protein diet was adequate to meet the protein requirements of catfish. However, in two of the studies, either dressed yield was slightly lower or fillet fat was slightly higher in fish fed a 28% protein diet as compared with those fed 32%. Since this response was not consistent among the experiments, and since we had hand dressed the fish ourselves, another experiment was conducted to compare 28% and 32% protein diets. The difference in this experiment was that the fish were processed using commercial equipment or hand filleted by employees from local processing plant to mimic commercial conditions.

There were no differences in feed consumption or weight gain regardless of diet (Table 12). Feed conversion ratio was lower in fish fed the 28% protein diet. This response is inconsistent with those of the other studies and is not likely due to diet. There is no reason to expect fish to convert the 28% protein diet any better than a 32% protein diet. There were also no differences in percentage visceral fat or in carcass, fillet, and nugget dressout between fish fed the two diets (Table 12). These data indicate that there are no differences between growth and dressed yield of fish fed either a 28% or a 32% protein diet.

Protein Quality

Experiment 8 

Fish meals prepared from whole fish, such as menhaden or herring, are highly palatable and digestible sources of essential amino acids, energy, phosphorus, and other nutrients. However, there is interest in replacing fish meal in catfish feeds because it is expensive and its availability is often variable. Experiment 8 was conducted to evaluate a blend of meat, bone, and blood meal (65% protein) as a replacement for menhaden fish meal in catfish feeds. The blended product is a mixture of meat and bone meal and blood meal in proportions that mimic the nutritional profile of menhaden fish meal. The product is often less expensive per unit of protein than fish meal. In this study, channel catfish were fed a 32% protein diet with either 8% menhaden fish meal or 8% meat and bone/blood meal. Fish were fed once daily to satiation. 

There were no significant differences in weight gain, feed conversion ratio, visceral fat, carcass dressout, or fillet composition in fish fed the two diets (Table 13). Results suggest that meat and bone/blood meal is highly palatable to catfish and can be used to replace menhaden fish meal in catfish feeds completely.

Experiment 9 

Experiment 9 was conducted to evaluate the need for animal protein in catfish diets. Channel catfish were fed a 32% protein diet that contained either 8% animal protein (4% menhaden fish meal + 4% meat and bone/blood meal) or no animal protein (primary protein source was soybean meal). Fish were fed once daily to satiation.  

There were no significant differences in feed consumption, feed conversion, or weight gain of fish regardless of diet (Table 14). There were no differences in carcass dressout or fillet proximate composition between the two groups of fish. Fish fed the all-plant diet had a lower level of visceral fat. This was presumably because the all-plant diet contained less digestible energy than the diet containing animal protein. These data indicate that animal protein is not needed in channel catfish diets, at least not for fish stocked at a large size (0.4 pound).

Experiment 10 

Experiment 10 was conducted to compare an all-plant diet and diets containing animal protein at two protein levels, 28% and 32%. Fish were fed once daily to satiation. There were no differences in feed consumption, feed conversion, weight gain, visceral fat, or body composition of fish regardless of diet (Table 15). These data show that an all-plant diet can be used for catfish grow out without detrimental effects using fingerlings of the size typically stocked in commercial ponds. In addition, the data also show that an all-plant diet containing 28% protein is as effective as a similar diet containing 32% protein.

Experiment 11 

Experiment 11 was conducted to compare diets containing graded levels of protein (26%, 28%, or 32%) and varying levels of animal protein (0%, 2%, 4%, or 6%). Meat and bone/blood meal was used as the source of animal protein. Fish we re fed once daily to satiation. 

There were no significant differences in feed consumption, feed conversion, or weight gain among fish fed the various diets (Table 16). Comparing the data averaged over all treatments, fish fed the 26% protein diet had a slightly lower carcass dressout as compared with fish fed the 28% and 32% protein diets (Table 17). These data indicate that animal protein is not essential for channel catfish, even when the dietary protein is reduced to as low as 26%.

Summary