# Effects of Water Temperature on Growth, Hematological Measurements and Stress-Related Gene Expression of Atlantic Salmon (Salmo salar) Parr Reared in a Recirculating Aquaculture System

## TL;DR

The study found that 14°C is optimal for Atlantic salmon growth and antioxidant activity, though some stress indicators suggest mild physiological trade-offs.

## Contribution

The study identifies 14°C as the optimal temperature for growth and antioxidant activity in Atlantic salmon parr, while revealing mild stress responses.

## Key findings

- Growth rate and feed efficiency were highest at 14°C with strong antioxidant activity.
- Molecular stress markers increased at higher temperatures, indicating mild physiological trade-offs.
- Heat shock proteins increased with temperature, while IGF binding proteins decreased at 18°C and above.

## Abstract

Atlantic salmon farming is influenced by water temperature, which can affect growth, feeding behavior, and overall health. In this study, juvenile salmon were raised for two months, at temperatures of 10, 14, 18, and 22 °C to assess their performance under different conditions. The growth was fastest at 14 °C, accompanied by efficient feed utilization and strong antioxidant activity. Most health indicators remained stable; however, some stress and immune responses varied at higher temperatures. These results suggest that 14 °C is close to optimal for growth and overall balance, though this temperature may still induce mild stress. Understanding these effects can help farmers select water conditions that enhance both productivity and fish welfare in sustainable aquaculture.

Water temperature is a key factor affecting the growth, feeding performance and physiological status of Atlantic salmon parr in aquaculture. To determine optimal conditions, parr (average weight 31.27 ± 0.35 g) were reared for 60 days at 10, 14, 18, and 22 °C. The survival and condition factors were similar across treatments. The growth rate and feed efficiency were highest at 14 °C, coinciding with elevated antioxidant activity. Feed intake was lowest at 10 °C. Whole-body protein and lipid contents remained unaffected, while moisture and ash contents were lowest at 14 °C. Most plasma biochemical indicators were stable; however, total protein was lowest at 14 °C. Glutathione peroxidase activity peaked at 14 °C, whereas cortisol levels remained unchanged. Heat shock proteins (HSP70, HSP90) increased with temperature, while insulin-like growth factor binding proteins (IGFBP1A, IGFBP1B) decreased at temperatures equal to or greater than 18 °C. Interferon alpha (IFNA) and thioredoxin (TRX) were lowest at 14 °C and highest at 22 °C. Overall, 14 °C appears optimal for growth and antioxidant capacity, although molecular stress markers suggest mild physiological trade-offs. These findings can inform temperature management strategies to enhance productivity and welfare in sustainable salmon aquaculture.