Effects of Randomly Fired Underwater Currents as an Occupational Enrichment Program in Rainbow Trout (Oncorhynchus mykiss)

Abstract

Occupational enrichment (OE) is directed at introducing variations in the tank water so that fish can exercise as they do in the wild. Two trials were carried out to test the effects of randomly fired underwater currents (RFC) on rainbow trout (Oncorhynchus mykiss) maintained in tanks in a recirculation system, using 1226 trout distributed in two independent trials. In Trial 1, fingerling trout (n = 6 tanks, n = 40 fish per tank) were classified into two groups based on low (13%) or high (30%) coefficient of variation in live weight (CV), and exposed to RFC or no currents (controls). In Trial 2, adult trout (n = 12 tanks, n = 20 fish per tank) were either exposed to RFC or to a constant current (controls) from two submerged pumps. Both trials lasted four weeks. No significant differences in growth were observed between treatments in either trial. In Trial 1, RFC fish maintained a similar CV throughout the trial, while CV decreased in controls. Also, in Trial 1, plasma cortisol levels were higher and creatine phosphokinase (CPK) levels lower in tanks with a low initial CV. In Trial 2, the CV was lower in RFC trout, where cortisol levels were also significantly lower and triglycerides significantly higher. The results suggest that OE using RFC can have positive effects by helping to reduce stress levels, and provides fish with biologically meaningful environmental enrichment related to the natural history of the species.

Environmental enrichment improves growth and fillet quality in rainbow trout

“…Depending on the type of OE, it can circumvent the use of physical structures while providing new stimuli in the environment, as described by Villarroel and co-workers. 9,10 To our knowledge, there are not many articles that have analysed the effect of EE on fillet quality, and the existing ones are based on nutritional enrichment, akin to that described by Rodríguez and Rojas. 11 In contrast, there are studies on the effect of OE on growth rate, 12 survival rates, 13 or stress and aggression.…”

“…Few of the enrichment types studies so far have been adopted on a commercial level, partly since the introduction of structures in tanks increases workloads (to clean and disinfect new elements), requires monitoring, and can lead to fouling. Depending on the type of OE, it can circumvent the use of physical structures while providing new stimuli in the environment, as described by Villarroel and co‐workers 9,10 …”