IMPACTS ON RAINBOW TROUT Onchorhynchus mykiss REARING PERFORMANCE OF DIETARY BIO-PROCESSED PLANT-BASED PROTEIN AND WATER VELOCITY

Michael L. Brown*, Jill M. Voorhees, Michael E. Barnes, and Steven R. Chipps
 
Department of Natural Resource Management
South Dakota State University
Brookings, SD 57007
Michael.brown@sdstate.edu
 

Carnivorous fish species, like rainbow trout, Onchorhynchus mykiss, require high levels of dietary protein.  Historically, fish meal (FM) has been the primary protein source, but its supply is variable, limited, and relatively expensive. Alternative protein sources are needed to meet the dietary protein demand for ever-increasing aquaculture production. In addition to specific dietary requirements, salmonids may react positively to exercise during hatchery rearing, with increased growth and feed conversion. While fish meal alternatives have received considerable research focus, no studies have examined the use of plant-based diets in conjunction with exercise.

 Two experiments, using different rainbow trout strains (Erwin x Arlee and Shasta), examined the dietary replacement of fish meal with a novel fermented soybean meal (FSBM) product. The dietary treatments were either FM or FSBM replacing 60% or 80% of the dietary FM. Flow treatments were the minimal velocity (averaging 3 cm/s for both experiments) required to keep tanks self-cleaning or an elevated level six to ten times that of the minimal velocity, depending on the experiment.

Feed conversion ratio (FCR) was significantly improved in fish fed diets where 60% of the FM was replaced with FSBM (Table 1). However, specific growth rate (SGR) was not significantly different among the diets with either strain. There were also no significant differences in trout weight, length, condition factor, relative fin length, hepatosomatic index, splenosomatic index, or viscerosomatic index among the dietary treatments. None of the dietary treatments were significantly affected by water velocity. However, compared to lower water velocities, higher velocities produced significantly poorer FCR and SGR in Shasta strain rainbow trout (Table 2). FCR was also significantly higher in the high velocity tanks of the Erwin-Arlee strain, but SGR was not significantly different between the velocities. With the Shasta strain, both the hepatosomatic and viscerosomatic indices were significantly different between the velocity treatments.  Fin indices were not significantly different between the velocities in either strain.

In conclusion, up to 80% of the FM component of Shasta strain rainbow trout diets can be replaced with FSBM with no decrease in rearing performance.  Also, up to 60% can be replaced in Erwin x Arlee diets.  Diets containing FSBM produced similar results to the FM control under both rearing velocities. However, higher rearing velocities generally led to poorer growth and FCR.