Elevated total dissolved gas (TDG) levels have been demonstrated to be detrimental in both natural environments and aquaculture settings for many species of fish. The current EPA standard for aquaculture water supplies is that total dissolved gas may not exceed 110% saturation. Gas bubble trauma has been demonstrated for fish species when TDG is above 110% saturation. In hatchery settings utilizing spring or well water, naturally occurring TDG levels of 104% or higher can occur. Detrimental effects of chronic TDG concentration have been variably demonstrated across fish species as well as life stages but limited information is available for cutthroat trout species in early life stages.
To test the effects of elevated TDG on four species of cutthroat trout a 3 x 4 factorial experiment was conducted with TDG concentrations of 100, 104 and 108% saturation with Bonneville, Snake River, Yellowstone, and Greenback cutthroat trout. The culture system consisted of 12 head boxes providing water to 3 tanks each. Four head boxes were allocated to each of the 3 TDG concentrations. The 78 L aluminum tanks received 1 l per min flow through water. Timing of stocking varied for each species due to spawn date. One hundred eggs were stocked in 4 replicate tanks per TDG treatment. Survival and fry size was quantified at hatch, first feeding, and 28- and 56-days post first feeding.
Factorial ANOVA was performed on survival and growth data with TDG and Cutthroat species as the main effects. No interactive effects were observed for TDG concentration and species for survival at any period. Total dissolve gas concentration and cutthroat trout species affected hatch rate with increasing TDG reducing hatch success. TDG did not affect survival from hatch to first feeding, but species effects were observed. Survival at day 28 and 56 were also reduced in the 108% TDG treatment group. Survival rates differed between species with Bonneville cutthroat surviving best and Greenback cutthroat generally surviving worst.
Fish mass at each sampling period were affected by both TDG concentrations and species. Fish mass was lowest for fry reared in 108% compared to 100% TDG with 104% being intermediate. Interactive affects were only observed in the 56-day fish mass with 104 and 108% TDG saturation reducing fish size in Yellowstone and Greenback cutthroat trout and no affect observed in Bonneville and Snake River cutthroat trout. Fish condition score and gill inflammation observations were largely undetectable at day 56. Chronic low levels of elevated total dissolve gas levels appear detrimental to cutthroat fry survival and growth.