Crude Protein in Commercial Catfish Diets

Commercial catfish feed comes in a variety of pellet sizes--floating or sinking pellets--and a variety of crude protein levels. The two most common levels are 28 percent and 32 percent crude protein. Farmers choose a particular formulation based upon growth and profitability. Of course, there has been considerable debate on which protein level leads to maximum growth.

Why would it be desirable to limit the total crude protein in practical diets? There are three nutrient groups that can provide energy-fat, carbohydrate and protein. Of these, protein is the most expensive. Reductions in protein content, without a reduction in growth, reduce feed costs. Excess dietary protein is catabolized preferentially over fats and carbohydrates for energy, so it is not available for growth. In addition, excess protein in the diets will lead to greater total nitrogen levels in the pond, fostering troublesome algae growth.

Since it is desirable to limit total dietary crude protein, which level is best? Current research seems to indicate that maximum growth of catfish can be achieved with practical diets containing a crude protein level of 28 percent. The following are representative examples.

In 1999, Robinson and Li fed fish diets containing 24, 28 or 32 percent crude protein, at rates of 80, 100, or 120 lbs/acre/day or to satiation. Results indicated that there were no differences in weight gain based upon the crude protein level. Fish fed at rates below satiation or below 120 lbs/acre/day experienced reduced growth. Visceral fat increased with the amount of feed fed, and higher visceral fat and lower dress-out occurred in those fish fed diets with a 28 percent crude protein. Dietary crude protein had no effect on fillet composition.

In 2002, Ruebush and Engle fed fish to satiation every other day-diets containing 28 or 36 percent crude protein. The results indicated no significant differences in feed conversion ratio, and mean harvested weight and growth of fingerlings and carry-over fish. There were also no significant differences in gross and net yield of carryover fish.

These types of results correspond with those of one of the first channel catfish nutrition studies, conducted more than 40 years ago. In 1962, Nail and Shell fed fish at a restricted rate, diets with crude protein levels of 6.3, 15.8, 25.3 or 34.8 percent. Weight gain of fish fed 25.3 percent crude protein was higher than those fed 6.3 or 15.8 percent crude protein, but not significantly different than those fed diets with 34.8 percent crude protein.

Some studies show that fish will grow better when fed diets containing a 32 percent or higher crude protein, but these studies involved feeding at a restricted rate. This is not desirable for several reasons.

First, if the farmer is not feeding to satiation, maximum growth is not obtained. Numerous studies have shown that fish fed at restricted rates do not grow as fast as those fed to satiation. They simply do not receive as much food as they can convert into flesh.

A second reason has to do with the under-stocked fish. Most catfish ponds are kept in continual production until the pond needs to be rebuilt. Market sized fish are harvested several times a year, and then the ponds are partially restocked with smaller fish. In these ponds, the smaller stockers are outcompeted for food by the bigger fish. Where the fish are fed at a restricted rate, the under-stocked fish do not receive as much feed and therefore take longer to reach a market size.

Finally, protein is the most expensive feed ingredient. Thirty-two percent crude protein feed is typically $8-12 more expensive per ton than 28 percent crude protein feed. Over the course of a summer of feeding, this price difference adds up.

Other variables are considered during diet formulation. These include digestibility of different crude protein sources, essential amino acid profiles of different feedstuffs, and the essential amino acid requirements of channel catfish.


By George Selden, Extension Aquaculture Specialist
Arkansas Aquafarming newsletter (Vol. 21, No. 1)
University of Arkansas Cooperative Extension