Structural Complexity Improves the Rearing Performance of Rainbow Trout in Circular Tanks

Abstract

While structural complexity has been used extensively during hatchery rearing in an attempt to improve poststocking survival, the potential impact of this complexity on hatchery rearing performance has largely been ignored. This study examined the growth and condition of juvenile Rainbow Trout Oncorhynchus mykiss reared in nearly fully covered circular tanks containing nine vertically oriented round aluminum rods (structurally complex) compared with that of trout reared in almost fully covered tanks with no rods (control) at two water velocities (2.0 body length (BL)/s and 2.75 BL/s). After 51 days, total tank weight gain was significantly higher in the structurally complex tanks than in the control tanks, regardless of water velocity. The feed conversion ratio was also significantly better in the structurally complex tanks [mean (SD) 1.25 (0.10)] than in the control tanks [1.66 (0.41)]. There were no significant differences in hepatosomatic index, splenosomatic index, and viscerosomatic index between the fish from the structurally complex and the control tanks. Total tank weight gain was significantly higher and the feed conversion ratio significantly lower in the lower water velocity tanks than in the higher water velocity tanks. These results indicate that vertically oriented aluminum rods can be used to increase structural complexity and improve Rainbow Trout rearing performance in circular rearing tanks, with minimal effects on regular tank cleaning.

Use of Bottom Structure and Tank Cover during Rainbow Trout Rearing in Circular Tanks

“…These results are similar to Brockmark et al [9], who found no significant difference in fish rearing performance with the addition of plastic plants and rocks to tank bottoms. Although neither this study nor Brockmark et al [9] found significant benefit with the use of environmental enrichment, benefits from the addition of structure in tanks has been found in other studies [2,6]. One difference that could account for the significant results of Kientz and Barnes [6] is the placement of structure in the tank.…”

“…Although neither this study nor Brockmark et al [9] found significant benefit with the use of environmental enrichment, benefits from the addition of structure in tanks has been found in other studies [2,6]. One difference that could account for the significant results of Kientz and Barnes [6] is the placement of structure in the tank. Both this study and Brockmark et al [9] added structure to the tank floor while Kientz and Barnes [6] suspended structure from tank covers.…”

“…One difference that could account for the significant results of Kientz and Barnes [6] is the placement of structure in the tank. Both this study and Brockmark et al [9] added structure to the tank floor while Kientz and Barnes [6] suspended structure from tank covers. As also observed by Baynes and Howell [13], the presence of the concrete blocks in this study interfered with the self-cleaning nature of circular On 7 November, 2014, 2,000 (2.72 kg) rainbow trout (mean ± SD, weight 1.36 ± 0.32 g, length 50 ± 4 mm; N=30) were placed into each of the 12 tanks.…”

“…The use of environmental enrichment can be beneficial during salmonid rearing [2,6], but not all enrichment techniques are equally effective in improving fish rearing performance. The use of concrete blocks on tank floors as a method of enrichment is not recommended because of a lack of significant effect on fish growth, as well as increased demands on routine cleaning.…”

“…Previous studies examining environmental enrichment techniques have noted that the addition of structure may increase competitive behavior and foraging skills in domesticated fish [2][3][4] as well as improve fish swimming ability and adaptability to new environments [5]. Vertically-suspended structure has also been observed to improve fish weight gain during hatchery rearing [6].…”