Xanthophyll in Catfish: Response Under Controlled and Outdoor Conditions

Abstract

Catfish industry is the largest component of aquaculture in the United States of America. It is a mature industry with more than 50 years of successful production, yet it faces various challenges while it adapts to shifting inputs and market demands. Dramatic increases in the price of feed ingredients and requests for more consistent fillet color are two core concerns of the industry. To help meet these challenges, a series of studies were conducted to evaluate lower cost feeds and the response of fish to xanthophyll levels of the feed. To help reduce the cost of diets, a pond study was conducted to evaluate the utilization of two alternative feeds including 20% corn gluten feed and two traditional feeds, with 28% or 32% protein, for the production of channel-blue hybrid catfish. After a summer growing season, no significant differences were found in growth performance, feed utilization, hematology, and immune response indices among the four treatments. However, intraperitoneal fat ratio was significantly lower in fish fed the alternative feeds and hepatosomatic index was higher in fish fed 28% protein feeds. Xanthophyll levels in fish fed alternative diets were significant higher, but without discernible yellow color. Xanthophyll levels in diets and in fillet were linearly related. These data generally indicated that channel-blue hybrids could efficiently utilize all the four experimental diets with satisfying production result. To help the catfish industry better understand the yellow coloration of catfish fillet, a color standard was developed with a digital camera and computer software. CIE LAB B value was used to indicate the yellowness. Lutein, zeaxanthin and alloxanthin were detected in the catfish fillet. A linear correlation was found between the B values and xanthophyll levels in catfish fillets. This color standard provides a means to sort fillets into different categories for different markets and can furthermore help with development of color management practice in catfish industry. An indoor aquarium trial was conducted to evaluate the deposition and depletion rate of xanthophyll in channel catfish fillet under various dietary treatments. The deposition experiment indicated that xanthophyll accumulated in fish flesh first and then trended to level off around a certain level related to the dietary xanthophyll level. Xanthophyll levels in fish fillets and in diets were linearly correlated after 16 weeks of culture. The dissipation experiment indicated that xanthophyll levels decreased linearly over 8 weeks. No difference was found in the dilution rate between diets with xanthophyll levels of 4.1ppm and 9.0ppm. Fish with higher initial xanthophyll level appeared to have a faster reduction in xanthophyll levels. To better understand the contribution of natural foods to xanthophyll level in catfish, a study was conducted to identify if there were correlations of xanthophyll in catfish fillet and in natural productivity under pond conditions. Catfish fillet and field samples (plankton, shad and snail) were collected and analyzed quantitatively for xanthophyll levels through HPLC. A correlation between xanthophyll level in catfish fillets and in microorganisms (>75 microns) was found. Natural productivity consumed by gizzard shad also contributed to the xanthophyll level in catfish fillet.