Abstract
This study evaluated the effects of two water velocities and three types of vertically-suspended environmental enrichment during the rearing of juvenile rainbow trout (Oncorhynchus mykiss; mean ± SE, initial weight 4 ± 1 g and total length 71 ± 2 mm) in 1.8m diameter circular tanks. The 2 × 3 experimental design used two velocities (12.2 cm·s-1 and 30.5 cm·s-1) and three structural treatments (aluminum rod array, plastic spheres, or no structure). After 116 days, the fish reared without any structure (control) at 30.5 cm·s-1 had significantly lower total tank weight, gain, percent gain, feed conversion ratio, and specific growth rate compared to the other treatments. Similarly, the fish reared with a velocity of 30.5 cm·s-1 without structure were significantly shorter and lighter than those in the other treatments. There was no significant difference in condition factor and relative fin lengths among the treatments. These results indicate that vertically-suspended environmental enrichment may be impacting fish rearing performance by altering tank water velocities.
Highlights
Environmental enrichment in fish culture has been categorized into physical, sensory, dietary, social, or occupational enrichment [1] [2]
Significant interactions were observed between the velocity and structure treatments with total tank weight, gain, percent gain, feed conversion ratio, and specific growth rate
Subsequent analysis indicated that fish reared without any structure at the higher velocity had significantly lower total tank weight, gain, percent gain, feed conversion ratio, and specific growth rate compared to all the other treatments
Summary
Environmental enrichment in fish culture has been categorized into physical, sensory, dietary, social, or occupational enrichment [1] [2]. Physical enrichment involves alteration of the rearing environment to increase complexity, such as by adding structure. Sensory enrichment comprises of rearing techniques that stimulate the fish senses, while dietary enrichment relates to changes in food types or delivery. Social enrichment comprises anything affecting interaction with. Exercise is the primary type of occupational enrichment. There can be overlap among these categories. Adding structures to rearing tanks (physical enrichment), may very well lead to sensory stimulation (sensory enrichment), interaction among the fish (social enrichment), and impact in-tank velocities (occupational enrichment) [3] [4]
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