Feeding juvenile largemouth bass (Micropterus salmoides) with carboxymethyl cellulose with different viscous: Impacts on nutrient digestibility, growth, and hepatic and gut morphology

Abstract

A 56-day trial investigated the impact of the dietary inclusion of cellulose with different viscosities on the growth, nutrient digestibility, serum biochemical indices, and the hepatic and gut morphology of largemouth bass juveniles. Four practical diets (42.50% protein and 13.70% lipid) were designed containing 8% microcrystalline cellulose (MC) and carboxymethyl cellulose (CMC) of 2,500, 5,000, and 6,500 mPa s dynamic viscosity [named MC, low-viscosity CMC (Lvs-CMC), medium-viscosity CMC (Mvs-CMC), and high-viscosity CMC (Hvs-CMC) groups, respectively]. Fish of a uniform size (6.0 g) were randomly assigned into 16 cages, with 40 fish per cage. The results showed that the protein and lipid deposition rates, specific growth rate, protein efficiency ratio, and the weight gain rate decreased significantly in the CMC groups compared to the MC group, whereas the feed intake and feed coefficient rate exhibited the opposite trend. Moreover, the intestinal Na+/K+-ATPase, alkaline phosphatase, and lipase activities significantly decreased in the Mvs-CMC and Hvs-CMC groups compared to the MC group, as well as the serum triglyceride, total cholesterol, and high-/low-density lipoprotein contents. The nutrient apparent digestibility significantly decreased in the CMC groups compared to the MC group. The viscerosomatic and intestinal length indices in the CMC groups and the villus height in the Hvs-CMC group were significantly lower than those in the MC group, whereas the number of gut goblet cells and muscular thickness in the Mvs-CMC and Hvs-CMC groups exhibited opposing results. The results also showed that dietary CMC damaged the hepatic and gut morphology and decreased the digestive enzyme activity, nutrient apparent digestibility, and growth of largemouth bass. In summary, viscosity is the main anti-nutritional effect of dietary CMC and soluble non-starch polysaccharides.