Dietary inclusion of salmon testes meal from Alaskan seafood processing byproducts: Effects on growth and immune function of rainbow trout, Oncorhynchus mykiss (Walbaum)

• We investigated the effects of testes meal on growth and immunity of rainbow trout.
• Testes meal inclusion had no effects on growth.
• Intermittent stimulation of innate immunity was observed in fish fed testes meal.
• Antibodies in testes meal or Macrogard fed fish were lower than those in fish meal controls.

This study investigated the growth and immune function effects following partial replacement of fish meal with dried testes meal from pink salmon (Oncorhynchus gorbuscha) testes collected from Alaskan seafood processing byproducts. It was hypothesized that the dietary nucleotide content of testes meal may provide an immunostimulatory effect in rainbow trout (Oncorhynchus mykiss). Three diets were formulated and used for this study; a commercial type control diet, a Macrogard diet, and an experimental diet containing 50 g kg− 1 testes meal. Triplicate groups of juvenile rainbow trout (8.65 ± 0.13 g fish− 1) were fed each diet for 12 weeks, at which time they were challenged with Flavobacterium psychrophilum (the causative agent of coldwater disease). No significant differences in feed conversion ratio or specific growth rates were observed. Kidney macrophage (phagocytic) activity was significantly (P < 0.05) increased in fish fed the testes meal at weeks 2 and 10 when compared to fish fed the control or Macrogard diets. At 12 weeks; however, this activity was significantly lower (P < 0.01) in fish fed either the Macrogard or the testes meal diets compared to fish fed the control diet. Following pathogen challenge, fish fed either the Macrogard or testes meal diets had significantly lower (P < 0.05) antibody titers at 8 weeks post challenge. The findings suggest that inclusion of testes meal can stimulate some innate responses; however, prolonged feeding of this or glucan based diets may be counterproductive and affect specific antibody development.