Seawater transfer time, alternative marine-based feed, and feeding regimes to improve smolt quality in farmed Atlantic salmon
Short description
Smoltification is a transitional stage in which Atlantic salmon parr prepare for a life in seawater while still in freshwater. High-quality smolts- characterized by increased hypo-osmoregulatory ability, optimal growth, efficient feed conversion, and stress resilience are essential for successful aquaculture. However, poor smolt quality remains a challenge in salmon farming, leading to higher mortality rates, increased disease risks, and growth issues, particularly in the first months following seawater transfer.
This research project is a part of a bigger project “Physiology shapes the -happy salmon” and the main aim is to improve smolt quality using osmoregulatory physiology and feeding innovations.
Smoltification in salmon farming
Smoltification, or the parr-smolt transformation, is an important life stage in the Atlantic salmon life cycle, where freshwater parr transform into a seaward migrating smolt. During this process they prepare themselves to adapt and survive in seawater long before they enter the marine environment to grow out.
In Atlantic salmon farming, the production cycle follows the life cycle. Once smoltification is complete, fish are transferred from freshwater hatcheries to seawater cages or net pens. Unlike in the wild, where the timing of the seaward migration is dictated by environmental cues, fish farmers must decide when to transfer smolts into seawater. Accurately tracking smoltification is therefore essential. Traditionally, gill Na+ K+ ATPase (NKA) enzyme activity has been the primary method to assess seawater readiness. However, incomplete smoltification can result in poor growth and high mortality rates after seawater transfer, particularly in the first few months. This is one of the major concerns in Norwegian salmon farming. To minimize these risks, it is crucial to ensure that smolts are fully prepared for the transition.
Recent advancements in smolt production protocols and intensive aquaculture practices suggest that gill-based indicators alone may not consistently reflect complete smoltification. This research project aims to adopt a holistic approach by evaluating multiple osmoregulatory organs—gill, kidney, and intestine—and their synchronized upregulation of NKA activity to determine optimal smoltification and seawater transfer time.
Furthermore, the project investigates nutritional strategies to enhance smolt quality. One key approach involves utilizing aquaculture side-streams, such as kelp and Ulva, as two different substrates for black soldier fly larvae. The resulting insect meal is then used as a sustainable protein source in juvenile Atlantic salmon diets. This strategy is expected to support fish growth while contributing to a circular economy.
