Addition of Vertical Enrichment Structures Does Not Improve Growth of Three Salmonid Species during Hatchery Rearing

Abstract

Environmental enrichment is the placement of structure or other modifications in typically sterile hatchery rearing units.This study investigated the use of vertically-suspended aluminum rod arrays in covered circular tanks on the rearing performance of brown trout (Salmo trutta), Chinook salmon (Oncorhynchus tshawytscha), and Atlantic salmon (Salmo salar) in separate trials lasting 59, 78, and 125 days respectively. No significant differences were observed in gain, feed conversion ratio, individual fish total length, or individual fish weight between the enriched and unenriched treatments in any of the three trials.In addition, vertically-suspended structure had no significant effect on Atlantic salmon relative fin length. These experiments are the first to indicate no benefits during the rearing of salmonids using vertically-suspended enrichment.

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

“…These results differ from White et al [23], who reported no significant improvement in Atlantic salmon feed conversion or growth after 125 days of rearing with another form of vertically-suspended environmental enrichment in much smaller circular tanks. Study duration may be a crucial determinant for observing significant results.…”

“…Brockmark et al [12] observed no effect of environmental enrichment on Atlantic salmon growth after 123 days, but reported growth improvements with enrichment after 311 rearing days. 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].…”

“…Two different treatments were assigned to the six circular tanks (N = 3). Three control tanks were devoid of any internal structure, while three tanks contained vertically-suspended structure as environmental enrichment, as described by White et al [23]. All tanks were near fully covered by corrugated plastic overhead covers [24].…”

“…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. However, the 125-day study duration may not have been long enough to detect any effects from environmental enrichment with Atlantic salmon.…”

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

“…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. The lack of significant improvement in gain or feed conversion ratio in this study is surprising.…”