The effects of water hardness and alkalinity on the development of brook trout (Salvelinus fontinalis) eggs and fry in aquaculture

Background/Question/Methods

The ability of a stream to protect developing brook trout (Salvelinus fontinalis) eggs and fry from adverse effects from acidification and metal toxicity is controlled primarily by geology which influences water hardness, alkalinity, and acid-neutralizing capacity. Water hardness is vital to fish health because it affects the permeability of membranes for osmotic regulation precluding diffusive flow and losses of ions to the surrounding aquatic environment. This concept can be applied in aquaculture, which has becomes increasingly more important to provide high quality fish for augmenting natural fisheries and the global food supply. The focus of this research was on the effects of calcium and magnesium water hardness and alkalinity on the early stages of developing brook trout. Brook trout eggs and fry were reared in high and low levels of calcium and magnesium water hardness as well as high and low alkalinities at limited feed rates to determine differences in mortality, growth rate, feed conversion, hatch time and body condition. A pilot study was conducted in aquarium tanks in a laboratory. The follow-up phase is an effort to engage the community by working with Trout Unlimited and the Virginia Department of Game and Inland Fisheries ‘Trout in the Classroom’ program where students can participate by growing brook trout in one of the geochemical treatments and collecting data to be used in research.

Results/Conclusions

Preliminary results indicate a ‘home field’ advantage, where brook Trout hatched in water where the brood stock were reared and spawned and eggs were eyed, had the highest growth rates and mortality.  This was had a moderate level of calcium water hardness and alkalinity compared to other treatments.  The treatment with high calcium water hardness with high alkalinity also has high growth rates with low mortality.  These results suggest that the high calcium water hardness and alkalinity are advantageous to rearing of brook trout and could be maintained in some aquaculture settings to increase productivity. Furthermore, the “home field” advantage suggests there may be a genetic component from maternal effects in the development of brook trout possibly due to adaptation of a meta-population to a particular range of water hardness and alkalinity found in a particular stream or drainage basin. This could be applied to aquaculture in a customized approach to management of stocked trout to genetically fit the destination stream by matching the rearing conditions to the geochemistry of the stream.