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

Morris Villarroel,Genaro C. Miranda-de la Lama,Jesús De la Fuente,Elisabet González-de Chávarri,Fernando Torrent,Rubén Bermejo-Poza,Concepción Pérez

doi:10.3390/w13213057

Morris Villarroel, Genaro C. Miranda-de la Lama + Show 5 more

Open Access

https://doi.org/10.3390/w13213057

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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.

Highlights

Rainbow trout (Oncorhynchus mykiss) are native to tributaries of the Pacific Ocean in Asia and North America, and have been introduced worldwide for sport fishing and commercial aquaculture [1]
There was a significant interaction between coefficient of variation (CV) type and randomly fired underwater currents (RFC), since the final CV of high
The results suggest that Occupational enrichment (OE) with RFC did not appear to have important positive effects on growth, RFC trout tended to have a longer fork length compared to controls (Trial 1)

Summary

Introduction

Rainbow trout (Oncorhynchus mykiss) are native to tributaries of the Pacific Ocean in Asia and North America, and have been introduced worldwide for sport fishing and commercial aquaculture [1]. Environmental complexity is almost totally absent in many artificial rearing environments, such as aquaculture tanks, ponds and raceways [4]. These intensive systems are characterized by a high stocking density with high material and energy inputs, and possible negative impacts on water quality such as eutrophication and oxygen depletion [5].

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