# Natural cold freshwater temperatures and light regimes in Atlantic salmon smolt production can improve the sea phase performance

## TL;DR

Atlantic salmon smolts raised in cold freshwater and natural light conditions perform better in the sea phase than conventionally raised smolts.

## Contribution

This study demonstrates that natural cold freshwater rearing improves sea phase performance metrics in older Atlantic salmon smolts.

## Key findings

- Cold-reared smolts showed 2% to 74% better mortality rates compared to regional averages.
- Feed conversion ratios improved by 4% to 22% in cold-reared smolts.
- Superior product quality was 2% worse to 49% better in cold-reared groups compared to others.

## Abstract

A total of 5.4 million smolts of Atlantic salmon (Salmo salar) older than 15 months, were divided into 18 groups and followed after sea-launch. They were all produced in the freshwater stage by employing natural conditions including water temperature and light program. The smolt were reared at water temperatures that in winter is as low as +3 °C and is referred to as “cold smolt”. The 18 groups were transferred to 11 net pen locations in Norway. Mortality, Feed Conversion Ratio (FCR) and share superior of the 18 groups were analyzed after harvesting and compared with the average in the respective production regions (POs) where the fish had been located. When the “cold smolt” had been co-located with the conventionally produced smolt groups, the “cold smolt” where also compared with these.

The results indicate that the "cold smolt" performed better in the sea phase than both the average of all smolt in the respective production areas and compared to other smolts released at the same time at the same locations. Compared to the annual average in the same PO the “cold smolt” performed, from 2 % to 74 % better regarding mortality, from 4 % to 22 % better regarding FCR and from 2 % worse to 49 % better regarding superior product quality.