Evaluating the chronic effects of nitrate on the health and performance of post-smolt Atlantic salmon Salmo salar in freshwater recirculation aquaculture systems

Authors: DAVIDSON, JOHN - Freshwater Institute; GOOD, CHRISTOPHER - Freshwater Institute; WILLIAMS, CHRISTINA - Freshwater Institute; SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2017
Publication Date: 8/24/2017
Citation: Davidson, J., Good, C., Williams, C., Summerfelt, S. 2017. Evaluating the chronic effects of nitrate on the health and performance of post-smolt Atlantic salmon Salmo salar in freshwater recirculation aquaculture systems. Aquacultural Engineering. 79:1-8. https://doi.org/10.1016/j.aquaeng.2017.08.003.
DOI: https://doi.org/10.1016/j.aquaeng.2017.08.003

Interpretive Summary: Farmed production of Atlantic salmon in recirculation aquaculture systems (RAS) has emerged as a developing trend. These production systems provide a nutrient-rich environment in which nitrate accumulates as a end-product of nitrification, but chronic nitrate limits have not been established for Atlantic salmon. The long-term effects of two nitrate levels to post-smolt Atlantic salmon raised in freshwater RAS were evaluated. Nitrate-nitrogen levels of 100 mg/L did not negatively affect Atlantic salmon growth and health and were therefore deemed safe for Atlantic salmon culture under the conditions of this study. These findings guide important engineering criteria for Atlantic salmon production in freshwater RAS such as water exchange rate, maximum fish biomass, and feed loading rate. Production cost savings related to reduced water use, heat retention, and lower capital investment for nitrate removal are expected.

Technical Abstract: Commercial production of Atlantic salmon smolts, post-smolts, and market-size fish using land-based recirculation aquaculture systems (RAS) is expanding. RAS generally provide a nutrient-rich environment in which nitrate accumulates as an end-product of nitrification. An 8-month study was conducted to compare the long-term effects of “high” (99 plus or minus 1 mg/L NO3-N) versus “low” nitrate-nitrogen (10.0 plus or minus 0.3 mg/L NO3-N) on the health and performance of post-smolt Atlantic salmon cultured in replicated freshwater RAS. Equal numbers of salmon with an initial mean weight of 102 plus or minus 1 g were stocked into six 9.5 m3 RAS. Three RAS were maintained with high NO3-N via continuous dosing of a sodium nitrate stock solution and three RAS were maintained with low NO3-N resulting solely from nitrification. An average daily water exchange rate equivalent to 60 % of the system volume limited the accumulation of water quality parameters other than nitrate. Atlantic salmon performance metrics (e.g. weight, length, condition factor, thermal growth coefficient, and feed conversion ratio) were not affected by 100 mg/L NO3-N and cumulative survival was greater than 99 % for both treatments. No important differences were noted between treatments for whole blood gas, plasma chemistry, tissue histopathology, or fin quality parameters suggesting that fish health was unaffected by nitrate concentration. Abnormal swimming behaviors indicative of stress or reduced welfare were not observed. This research suggests that nitrate nitrogen concentrations less than 100 mg/L do not affect post-smolt Atlantic salmon health or performance under the described conditions.