Aquaculture Feed and Fertilizer Resources Information System
 

Channel catfish - Nutritional requirements

Protein requirements

The dietary protein and amino acid requirements of channel catfish have been extensively studied during the past three decades. The optimum protein levels in catfish diets are influenced by several factors, including fish age and size, dietary protein quality and source, non-protein energy in the feed, natural food availability, feeding levels and culture conditions (Page and Andrews, 1973; Winfree and Stickney, 1984; Cho and Lovell, 2002; Robinson and Li, 2002; Wu et al., 2004). The dietary protein requirement of channel catfish ranges from about 25–55 percent, depending on life stage (NRC, 1993). For example, Winfree and Stickney (1984) reported that channel catfish fry require 55 percent protein for optimum growth. Fingerlings and juveniles require a protein level of 36 to 40 percent, whereas 25 to 36 percent dietary protein is suggested for grow-out stages (Page and Andrews, 1973; Robinson and Li, 2002). Moreover, increasing dietary protein level in the diet of channel catfish broodstock from 32 to 42 percent did not influence spawning, fecundity or fertilization, but affected egg size and biochemical composition of the eggs (Quintero et al., 2009).

Protein requirement of channel catfish is also affected by feed allowance. Li and Lovell (1992) showed that when pond-raised channel catfish were fed to satiation, they require 28 percent protein for maximum growth. The fish require 32 percent or 36 percent protein for maximum growth when they are fed to less than satiation. Similarly, Robinson and Li (1997) found that when catfish in ponds were fed to satiation daily with diets containing 16–32 percent protein, the weight gain of fish fed 24 to 28 percent protein was similar, and higher than that of fish fed 16 percent, 20 percent or 32 percent protein.

A study at Auburn University (United States of America) (Prather and Lovell, 1973) showed that when channel catfish were fed diets containing high protein content (42 percent and above) and low amounts of non-protein energy (less than 1.5 kcal per g), fish growth was suppressed. When the protein level was reduced to 36 percent and the non-protein energy level remained the same, growth increased. When the non-protein energy in either the 42 percent or the 36 percent protein diets was increased, fish performance was improved. This study indicated that when excessive dietary protein was provided, the excess protein was catabolized into energy, leading to a reduction in feed utilization efficiency.

Amino acid requirements

Channel catfish require the same ten essential amino acids as other finfish (NRC, 1993). The quantitative essential amino acid requirements have been partially determined for channel catfish and have been found to agree with values reported for other species such as tilapia, carps and salmons. However, the sulphur amino acid requirement for catfish is lower than in salmonids. Recommended levels of essential amino acids for channel catfish are given in Table 1. Adding supplemental amino acids to low-protein diets to simulate a higher-protein diet may not improve catfish growth. For example, the addition of the limiting amino acids lysine and methionine to a 24 percent protein diet to simulate the levels of these amino acids found in a 32 percent protein diet did not enhance fish performance (Li and Robinson, 1998; Robinson and Li, 2005). This was because the 24 percent protein diets contained adequate levels of the essential amino acids. However, when fish fingerlings were fed a 22 percent protein diet, growth rates were significantly lower than those fed a 32 percent protein diet (Webster, Tiu and Morgan, 2000). Supplemental crystalline methionine and/or lysine did not improve fish growth.

Protein sources

Fishmeal (FM) has been widely used as the major protein source for many cultured fishes, including channel catfish. Earlier studies (Tucker and Robinson, 1990; Wellborn and Cichra, 1995) suggested that 60 percent of the protein in catfish fry diets should consist of FM. Mohsen and Love11 (1990) found also that FM-free diet reduced the performance of fingerling channel catfish.

Several studies have investigated the effects of replacing dietary FM with all-plant-protein diets on the growth of channel catfish, with varying and inconsistent results. Some studies showed that FM could be completely replaced by all-plant-protein sources without adversely affecting fish performance (Robinson and Li, 1994; Reigh, 1999). A recent study by Sink, Lochmann and Kinsey (2010) found that the growth rates of channel catfish fry fed all-plant-protein diets (soybean meal, SBM) were not different from those fed FM protein in diets. When the fish were fed diets with 36 or 45 percent protein and SBM or FM protein sources, their performance and survival were not significantly different. The authors concluded that there is no apparent advantage to the inclusion of animal protein in diets for channel catfish fry. Similarly, Li et al. (2010a) reported that nutritionally balanced all-plant protein diets could provide normal growth in pond-raised channel catfish fingerlings. However, all-plant diets may require additional supplemental phosphorus and the use of a mineral premix. The advantages of using all-plant diets include lower feed cost, milder flavour, and less body fat because of a reduction in dietary energy.

Cottonseed meal, canola meal, corn gluten feed and distillers’ grains can be used to partially or totally replace dietary SBM. However, at high inclusion rate (higher than 20–25 percent) supplemental lysine may be necessary. The inclusion of these ingredients will depend on their cost per unit of protein. Webster et al. (1997) found that that up to 36 percent of canola meal can be incorporated in catfish diets (4 percent FM) under favourable economic conditions. Li et al. (2010b) studied the effects of various distillers' by-products on the growth, feed efficiency and body composition of fingerling channel catfish. They found that the presence of distillers' solubles in the diet (300 g/kg distillers' dried grains with soluble (DDGS), 100 g/kg distillers' solubles (DS), 100 g/kg distillers' solubles from corn endosperm (EDS) diets) increased diet consumption, weight gain and feed conversion efficiency (FCE) over the control diets with or without additional dietary lipids. Similar results have been reported by Li, Oberle and Lucas (2011), who found that the inclusion of 30 percent DDGS in plant-protein diet provided the same level of growth and PER as the FM-based control diet.

Many other studies have indicated that FM can be partially or totally replaced by animal proteins. Poultry by-product meal, meat and bone meal, blood meal, catfish offal meal, hydrolyzed feather meal plus lysine, or a combination of these protein sources can be effectively used as FM replacers for channel catfish (Robinson and Li, 2007a).

In a recent study, Peterson, Booth and Manning (2012) examined the effects of replacing FM with a yeast-derived protein source (NuPro) at six levels (0, 25, 50, 75, 100 and 125 g/kg) on growth rates, feed utilization, body composition and disease resistance of juvenile channel catfish. Results indicated that up to 100 g/kg) of NuPro can be added without negatively affecting growth performance. Further increase in NuPro to 125 g/kg resulted in a significant reduction in fish performance. Fish survival after challenge with Edwardsiella ictaluri was similar among treatments regardless of the amount of NuPro added. In the same line, Li, Oberle and Lucas. (2011) found that brewers yeast, used at 1–2 percent of the diet improved weight gain and protein efficiency ratio (PER) of channel catfish fed all-plant protein diets.

Lipid and essential fatty acid requirements

The lipid requirements of farmed channel catfish have been studied by a number of authors, with varying results. These requirements depend on lipid source and quality, carbohydrate and protein content of the diet. The lipid concentration in commercial 28 and 32 percent protein diets ranges from 4 to 7 percent, about 3 to 4 percent of which is generally inherent in the feed ingredients. However, recent studies indicate that channel catfish may require higher lipid levels for optimum spawning performance. For example, Sink and Lochmann (2008) found that supplementation of catfish broodstock diets with 10 percent fish oil increased spawning success, fecundity, total egg volume, egg weight, total egg lipid concentration, hatching success and fry survival compared to a control diet with 4 percent fish oil.

The fatty acid (FA) requirements of channel catfish have been well studied, with varying and sometimes contradictory results. For example, Satoh, Poe and Wilson (1989) reported that channel catfish have the capability to elongate and desaturate linolenic acid (C18: 3n-3) to synthesize n-3 highly unsaturated fatty acids (HUFA), and therefore, they require 1 to 2 percent of linolenic acid for optimum performance. In support, Yildirim-Aksoy et al. (2007) found that the weight gain, feed efficiency and survival of channel catfish fed diets supplemented with 0–9 percent menhaden fish oil were not significantly different. However, tissue lipid contents were directly correlated to dietary lipid levels. Tissue FA contents, particularly n-3 and n-3 HUFA, and the ratio of n-3/n-6 FA increased with increasing dietary fish oil levels. Similar results were also reported by Yildirim-Aksoy et al. (2009). This is consistent with the previous findings of Lim et al. (2006), who reported that channel catfish performance was not significantly affected by dietary menhaden fish oil at levels ranging from 6 to 14 percent.

On the contrary, many studies reported that channel catfish fed diets containing fish oil (FO) or animal fat resulted in better growth than the diets containing only vegetable oils (VO) (Stickney and Andrews, 1972; Wilson and Moreau, 1996). These studies suggested that the poor performance of channel catfish fed VO was due to the limited ability of these fish to elongate and desaturate C18 fatty acid to HUFA. Thus an external source of n-3 HUFA is required for performance improvement (Li et al., 1994; Wilson and Moreau, 1996).

Several studies have recently been carried out to evaluate the effects of lipid source on growth, feed efficiency, reproductive performance and haematological parameters. For example, Sink and Lochmann (2008) studied the effects of dietary lipid source (poultry fat (PF) or menhaden fish oil (FO)) and level (4 or 10 percent) on egg biochemical composition, egg and fry production, and egg and fry quality of channel catfish broodstock. They found that spawning performances (spawning success, fecundity, total egg volume and egg weight) at 10 percent PF or FO were similar, and were higher than at 4 percent PF and FO. The authors also reported that catfish can synthesize long-chain HUFAs from 18-carbon precursors.

More recently, Quentero et al. (2011) evaluated the influence of different lipid sources and n3:n6 ratios on the reproductive performance of female channel catfish. A commercial diet was top coated with 2 percent oil and offered to broodstock females during 70–85 days before spawning season. Four dietary treatments were formulated using the following top-coating ratios: diet 1, soybean oil 0.95 percent and linseed oil 1.05 percent; diet 2, soybean oil 1.75 percent and linseed oil 0.25 percent; diet 3, 2.0 percent linseed oil; and diet 4, 1.0 percent menhaden fish oil supplemented with 0.50 percent arachidonic acid (ARA) and 0.50 percent docosahexaenoic acid (DHA).

The authors found that the fatty acid composition of the eggs reflected the effect of the dietary oils. The diet which was coated with menhaden fish oil supplemented with ARA and DHA produced two to five times the number of fry per female body weight when compared to the effect of feeding diets top coated with vegetable oils.

The fillets of channel catfish can be enriched with n−3 HUFA by feeding diets containing refined menhaden fish oil (Manning et al., 2006). This fish oil contains high levels of the n−3 HUFA of interest, such as eicosapentaenoic acid (EPA) and DHA. Similarly, dietary lipids affect different haematological factors of cultured channel catfish (Klinger, Blazer and Echevarria, 1996). When the fish were fed diets containing soybean oil, menhaden oil, beef tallow or a combination of these three lipid sources, fish fed the menhaden oil diet had significantly lower haematocrits, higher thrombocyte counts, and higher serum iron concentrations. They also had the highest concentration of n-3 fatty acids in the pronephros tissue, and their erythrocytes were the least susceptible to osmotic lysis. Catfish fed the beef tallow diet had the lowest level of n-3 fatty acids in pronephros tissue and their erythrocytes were the most susceptible to osmotic lysis. Similarly, Yildirim-Aksoy et al. (2009) found that the haematological values of catfish fed diets supplemented with menhaden fish oil at 0 to 9 percent were not significantly different, except at 9 percent fish oil, where haematocrit value was significantly lower. Fish fed 6 and 9 percent fish oil diets had significantly higher serum protein levels than control fish. Serum lysozyme activity of fish fed 3 and 6 percent added fish oil diets was significantly higher than that of the control.

Carbohydrates

Channel catfish are known to utilize polysaccharides (dextrin and starch) as efficiently as dietary lipids within certain carbohydrate-to-lipid (CHO:L) ratio (Wilson and Poe, 1985),  whereas mono- and disaccharides are not well utilized by these fish. Digestibility studies with channel catfish have indicated that they digest uncooked carbohydrate (starch) much better than salmonids. Cooking of feedstuffs during extrusion processing improves the digestibility  of most materials, especially those high in starch. Commercial channel catfish diets contain about 25 percent digestible carbohydrates.

Catfish also have low capability to digest crude fiber. Crude fiber should be kept at a very low level. Commercial catfish feeds typically contain less than 5 percent crude fiber (Robinson, Li and Hogue, 2006). In addition to providing an inexpensive energy source, starch helps bind feed ingredients together, increases expansion of extruded pellets, and improves their water stability and floating in the water.

Energy-to-protein ratio

Absolute energy requirements for catfish are not known. Estimates of the requirement have been determined by measuring the performance of catfish fed diets containing known energy levels. Energy requirements reported for catfish have generally been expressed as a ratio of digestible energy to crude protein (energy-to-protein (DE:P) ratio). This ratio ranges from 7.4–12 (Robinson and Li, 2007a). However, research carried out at Mississippi State University indicated that a DE:P ratio of 7.3–10 kcal/g is adequate for use in commercial catfish feeds (Li and Robinson, 1999; Robinson and Li, 2007a). Ratios above this range may lead to increased fat deposition, while at lower DE:P ratio, the fish will grow at slower rates.

Vitamins

The quantitative vitamin requirements of cultured channel catfish have not been well elucidated. The values of vitamins required by catfish are summarized in Table 2. Studies conducted in ponds in Mississippi (summarized in Robinson and Li, 2005) indicated that the growth rates of catfish fed diets containing a complete vitamin premix, one half of the recommended vitamins, one-fourth of the recommended vitamins or no supplemental vitamins were similar (Robinson and Li, 2005). These results indicated that catfish are able to utilize vitamins found in feedstuffs and/or natural pond organisms. These studies  also indicated that choline supplement is unnecessary, and that B-complex vitamins are highly stable during feed processing, and therefore their level could be reduced in the vitamin supplement used for catfish. This means that excessive vitamin supplementation is not needed in the diet to compensate for losses during feed processing.

It has also been reported that phosphorylated vitamin C was highly stable (70–80 percent) during extrusion processing of catfish feeds, and therefore was biologically available to the fish. Excessive levels of vitamin C are therefore not beneficial to channel catfish. Gaylord, Rawles and Gatlin (1998) reported also that the current level of vitamin E supplementation of commercial catfish diets may be reduced considerably with no detriment to channel catfish health or production. However, it should be noted that because of the variability of vitamin content  in feeds from different sources, catfish feeds should be supplemented with a vitamin premix. The refinement of vitamin supplementation in diets for pond-raised channel catfish has been reviewed by SRAC (1997).

In a recent study, Zuberi et al. (2011) studied the effects of varying levels of vitamin C supplementation given to channel catfish broodstock on ascorbate levels in their gametes and on growth of their offspring. The fish were offered 36 percent protein diets; a commercial diet containing ascorbic acid (control diet) at 100 mg/kg (C100) and two diets supplemented  with L-ascorbyle-2-polyphosphate (APP) at 500 (APP500) and 1 000 mg/kg (APP1000). After 70 days, there was an 82.4 percent loss of total ascorbic acid (TAA) in the commercial diet, while the recovery of TAA in APP500 and APP1000 diets was 95.4 and 91.7 percent, respectively, of the initial amount of vitamin C. Similarly, the concentration of TAA in unfertilized eggs in fish fed C100 was significantly lower than those fed APP500 and APP1000 diets. APP-supplemented diets also improved the quality of eggs compared with the commercial diet (control). The fry produced from the broodstock fed with APP500 and APP1000 diets showed higher growth performance as compared with the control group (C100).

Minerals

The dietary mineral requirements of channel catfish have been quantified based on specific clinical signs resulting from feeding the fish mineral-deficient feeds. Channel catfish can also obtain part of their mineral requirements directly from rearing water. For example, when the water is rich in calcium, the fish can meet their calcium requirement by absorbing calcium from the water. The minimum requirements of available phosphorus in channel catfish diets depend on the availability of phosphorus to the fish from various dietary sources. Plant proteins contain phytic acid which binds with divalent cations, making them unavailable for absorption in the gut, especially in the presence of calcium phosphate (Robinson and Li, 2005). Therefore, pond-raised channel catfish fed all-plant diets may require additional phosphorus in their feeds. Supplementing channel catfish feeds with microbial phytase, the enzyme that hydrolyzes phosphorus from phytate, may also increase the available phosphorus in catfish feeds.

Dietary requirements for most of other minerals have not been well elucidated for catfish. Natural feedstuffs are usually adequate in potassium, magnesium, sodium and chloride for normal growth of these fish. These elements are probably available in sufficient quantity in practical fish feeds without mineral supplementation. However, fish feeds low in animal products (fishmeal, meat and bone meal, etc.) may be deficient in trace minerals. The mineral requirements of channel catfish are summarized in Table 3.

Feed digestibility

Digestibility coefficients for protein, lipid, carbohydrate and energy of the major feed ingredients have been determined for channel catfish (Table 4). Most animal-based and plant-based protein sources are well digested. Lipids are also highly digestible by channel catfish, and are considered good energy sources for them. However, starches are not highly digested by the fish as compared to dietary lipids. Carbohydrate digestion decreases as the dietary level increases (Robinson, Li and Manning, 2001). Cooking of feedstuffs during extrusion processing improves the digestibility of most materials, especially those high in carbohydrates (starch). Commercial channel catfish diets contain about 25 percent of digestible carbohydrates. The major sources of carbohydrate in catfish feeds are grains and grain products, which are 60–80 percent digestible, depending on the source, inclusion level and processing.

Feed additives

Feed additives, including binders, antioxidants and antibiotics, are added to catfish feeds to improve their quality and performance. Binders are added to improve the quality of steamed pellets, increase their durability and improve their stability in water. Common pellet binders include the bentonites, which are clay compounds mined from deposits, and lignin sulfonates, which are by-products of the wood processing industry. However, extruded catfish feeds do not require additional pellet binder, because these feeds contain a high percentage of grain or grain by-products which improves feed gelatinization and expansion. The synthetic antioxidants used in channel catfish feeds include butylated hydroxianisole (BHA), butylated hydroxytoluene (BHT) and ethoxyquin. These compounds may be added to fats and sprayed on catfish feeds or added directly to feeds during mixing. United States Food and Drug Administration (FDA) permissible levels for BHA and BHT are 0.02 percent of dietary fat content; while for ethoxyquin, the permissible level is 150 ppm (Robinson, Li and Manning, 2001). Antibiotics are incorporated into feeds to be fed to catfish diagnosed with specific diseases. The main antibiotics added to catfish feeds are oxytetracycline (Terramycin®) and a combination of sulfadimethoxine and ormetoprim (Romet®).