GROWTH, IMMUNE RESPONSE, AND DISEASE RESISTANCE OF JUVENILE RAINBOW TROUT FED DIETS CONTAINING CRICKET MEAL, AND MEALWORM MEAL

Cheyenne E. Owens*, Madison S. Powell, T. Gibson Gaylord, Wendy M. Sealey
 
US Fish & Wildlife Service
Bozeman Fish Technology Center
4050 Bridger Canyon Rd.
Bozeman, MT 59718
cheyenne_owens@fws.gov
 

Insect meals may provide an alternative protein source to fish meal in salmonid feeds. Insect meals contain chitin, which can have low digestibility but has been shown to have an immune-stimulatory benefit to fish.

An 8-week feeding trial was conducted to determine whether cricket or mealworm meal could be used as a fish meal replacement in rainbow trout diets. Fish meal was replaced within a control diet at 25%, 50% or 100% of its inclusion level (FMR) with either cricket meal or mealworm meal. Two additional diets were formulated by supplementing the control diet with practical grade chitin from shrimp shells at rates mimicking chitin levels in the 25% and 100% FMR cricket meal diets. All nine diets were formulated on a digestible protein basis. Diets were randomly assigned to triplicate tanks of 5.5g initial weight rainbow trout, and the fish were fed twice daily to apparent satiation. Kidneys were sampled at 2 and 8 weeks in order to compare innate immune response genes. Subsamples of fish were challenged at 2- and 8- weeks post-feeding by 0.1 ml injection with 108 cfu/ml Flavobacterium psychrophilum and mortality was monitored for 28 days.

No significant differences in final weight, percent increase, FCR, HSI, or VSI were observed due to diet (Table 1). Mortalities were >80% for all treatments and no significant differences due to diet were observed at two-weeks post-feeding. No mortalities were observed in the 8-week challenge.  Proximate composition and innate immune response will be discussed.

These findings suggest that with proper formulation, insect meals can replace fish meal within rainbow trout diets. No negative effects of chitin on fish growth were observed; however, no immune benefits were observed when exposed to F. psychrophilum.