|SHELBY, RICHARD - US Department Of Agriculture (USDA)|
|LI, MENGHE - Auburn University|
Submitted to: Fish Physiology and Biochemistry Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2009
Publication Date: 11/1/2009
Citation: Lim, C.E., Aksoy, M., Shelby, R.A., Li, M.H., Klesius, P.H. 2009. Growth performance, vitamin E status, and proximate and fatty acid composition of channel catfish, Ictalurus punctatus, fed diets containing various levels of fish oil and vitamin E. Fish Physiology and Biochemistry Journal. 35: 683-693.
Interpretive Summary: Channel catfish have a dietary requirement for linolenic (n-3) and/or linoleic (n-6) series of fatty acids. However, cultured catfish are commonly fed soy-corn based feeds high in n-6 and low in n-3 highly unsaturated fatty acids (n-3 HUFA). Earlier research has shown that catfish fed diets supplemented with marine fish oil (high in n-3 HUFA) had significantly increased tissue levels of n-3 HUFA. This, coupled with the current public awareness of the health benefits of consuming fish high in n-3 HUFA, have stimulated interests among catfish producers in adding marine fish oil to catfish diets. However, it has been reported that the requirement of vitamin E in some fish species increased with increasing dietary levels of n-3 HUFA. Thus, this study was conducted to evaluate the effect of increasing dietary levels of fish oil on vitamin E requirement and their interaction on growth performance, whole-body proximate composition, whole-body and liver fatty acid composition, and liver vitamin E storage of channel catfish. Basal diets supplemented with 6, 10 and 14% menhaden fish oil were each supplemented with 50, 100 and 200 mg vitamin E/kg were fed to juvenile catfish to apparent satiation twice daily for 12 weeks. Results of this study indicate that, based on weight gain, FI, FER and survival, supplementation of vitamin E at 50 mg/kg was adequate for channel catfish fed diets containing 6 to 14% menhaden fish oil. For good survival and prevention of whole-body lipid accumulation, supplemental levels of fish oil should be less than 10%. Liver storage of vitamin E was directly related to dietary levels of vitamin E, but negatively related to dietary fish oil levels. However, significant reduction of liver vitamin E with increasing fish oil levels was observed only at the highest supplemental level of vitamin E (200 mg/kg diet). Liver lipid content was unaffected by dietary levels of fish oil, vitamin E or their interaction. HSI decreased with increasing dietary levels of fish oil, although the latter had no effect on liver lipid content. Vitamin E at a level of 50 mg/kg diet was sufficient to prevent fatty liver or degeneration of liver tissue. Fatty acid composition of whole-body and liver lipid generally reflected that of dietary lipid. Total n-3 and n-3 HUFA in both tissues increased with increasing dietary fish oil levels, but liver contained much higher levels of these fatty acids. This may be attributed to better protection of liver by its higher content of vitamin E than in muscle as has been previously reported.
Technical Abstract: A study was conducted to determine the effect of increasing dietary levels of fish oil on vitamin E requirement and their effect on growth performance, liver vitamin E status, and tissue proximate and fatty acid compositions of channel catfish. Basal purified diets (42% protein and 3,800 kcal DE/kg) supplemented with 6, 10 and 14% menhaden fish oil were each supplemented with 50, 100 and 200 mg vitamin E/kg (3 x 3 factorial experiment). Each diet was fed to juvenile channel catfish in three random aquaria to apparent satiation twice daily for 12 weeks. Weight gain, feed intake and feed efficiency ratio were not affected by dietary levels of fish oil, vitamin E or their interaction. Survival rate at the end of week 12 was significantly lower for fish fed diets containing 14% fish oil, regardless of vitamin E content. Whole body moisture significantly decreased and lipid increased when dietary lipid levels were increased to 10 or 14%. Dietary vitamin E levels had no effect on body proximate composition. Lipid content of liver was not influenced by dietary levels of fish oil and vitamin E or their interaction. Hepatosomatic index significantly decreased with increasing lipid levels but was not affected by dietary levels of vitamin E. Liver vitamin E increased with increasing dietary vitamin E but decreased with increasing fish oil levels. Fatty acid composition of whole body and liver reflected that of dietary lipid but was not influenced by dietary levels of vitamin E. Whole-body saturates increased, whereas monoenes decreased with increasing dietary levels of fish oil. Liver saturates were not affected by fish oil levels, but monoenes and n-6 decreased and increased, respectively with increasing fish oil levels. Total n-3 and n-3 HUFA in both tissues increased with increasing fish oil levels in diets, but liver stored much higher levels of these fatty acids.