Use of Suspended Plastic Conduit Arrays during Brown Trout and Rainbow Trout Rearing in Circular Tanks

Abstract

Environmental enrichment is the modification of otherwise sterile hatchery rearing units to provide structural complexity. We investigated the use of an array of suspended plastic conduit sections as enrichment in large circular tanks during two experiments. Brown Trout Salmo trutta and Rainbow Trout Oncorhynchus mykiss were reared for 126 and 61 d, respectively, in covered, 3.63‐m‐diameter circular tanks that were either void of any structure or enriched with a suspended array of twenty 0.94‐m‐long sections of plastic conduit. Total tank weight gain and feed conversion ratio were significantly improved for both Brown Trout and Rainbow Trout reared with suspended conduit as enrichment compared to unenriched tanks. Enrichment did not significantly affect individual fish length, weight, or condition factor in either experiment, likely because of small sample sizes. The suspended array did not interfere with tank hydraulic self‐cleaning. Based on the results of this study, the use of vertically suspended enrichment structures in circular tanks is recommended to improve trout rearing efficiencies.

Vertically-Suspended Environmental Enrichment Alters the Velocity Profiles of Circular Fish Rearing Tanks

“…The increase in fish growth and rearing efficiencies using arrays of suspended objects in circular tanks is well documented [27] [28] [29] [30] [31]. These fish rearing benefits are likely at least partially because of the dramatic in-tank velocity changes due to the suspended environmental enrichment.…”

“…These vertically-suspended structures were shown to significantly improve rainbow trout (Oncorhynchus mykiss) rearing performance [27]. Subsequent investigations evaluating various types of vertically-suspended structures, including strings of spheres, plastic pipes, and aluminum angles, have also indicated positive effects during the rearing of multiple salmonid species [28] [29] [30] [31].…”

Rearing Performance of Atlantic Salmon Grown in Circular Tanks with Vertically-Suspended Environmental Enrichment

“…Similarly, White et al [23] reported that vertically suspended structures did not produce any improvements in brown trout (Salmo trutta) or Chinook salmon (Oncorhynchus tshawytscha) growth at 59 and 78 days, respectively. However, improvements in rearing performance were reported for brown trout growth after 126 days [22] and Chinook salmon at 90 days [21]. [27] suggest that environmental enrichment techniques may need to be modified to fit the needs of individual fish species, the consistent results obtained using vertically-suspended structure appear to indicate a more universal response, at least among salmonids.…”

“…The use of vertically-suspended arrays as environmental enrichment is a recent development. In general, the suspension of vertical structures has improved feed conversion ratios and salmonid growth without disrupting circular tank self-cleaning [14] [22]. In contrast, White et al [23] did not observe improved hatchery rearing performance with the use of vertically-suspended arrays in juvenile Atlantic salmon (Salmo salar) during a 125 day study.…”

Use of Two Vertically-Suspended Environmental Enrichment Arrays during Rainbow Trout Rearing in Circular Tanks

“…The significant improvement in fish length, weight, and specific growth rate with either of the vertically-suspended angle environmental enrichment treatments is not surprising. Numerous other studies have documented improved salmonid growth using other vertically-suspended enrichment techniques [14][15][16][17][18][19]. However, White et al [23] reported no improvement in the growth of brown trout (Salmo trutta), Chinook salmon (Oncorhynchus tshawytscha), and Atlantic salmon (S. salar) reared in circular tanks with a relatively small array of vertically-suspended aluminum rods for relatively short time-frames.…”