Salmon that have fasted eat much more when they are fed again. In a research project, the consequences of such a strategy have been examined more closely.

New research: intermittent fasting as a production strategy

In an article in the journal Aquaculture, researchers from the University of Bergen and Norway's Institute of Marine Research have examined whether intermittent fasting can improve economics and production results for fish farmers.

Published

In the aquaculture industry, feed costs account for more than half of the operating expenses, making the optimisation of feed utilisation a central priority. The researchers write in the article that overfeeding has long been the norm, driven by the fear that low feed intake may hinder growth and profitability.

However, they pose the question of whether periodic fasting can provide farmers with a smarter strategy.

Scientific Article

Title: Adaptations to intermittent fasting in large sea caged Atlantic salmon (Salmo salar); effects on feeding, energy homeostasis, and growth

Published: Aquaculture

Funding: Norwegian Research Council

Researchers: Floriana Lai a); Ivar Rønnestad a); Thea Solberg Olsen a); Virginie Gelebart a); Pablo Balseiro a); Tone Vågseth b); Sigurd O. Handeland a); Ole Folkedal b)

a) UiB

b) Institute of Marine Research

In the study, they investigate this by analysing how large Atlantic salmon (over 3.3 kg) respond to being fed every third day for six weeks, followed by five weeks of daily feeding before harvest.

Reduced growth, increased appetite

The results from the study show that salmon that fasted periodically exhibited a significant increase in feed intake per meal, with a tripling of stomach content after feeding.

Despite this, they were unable to maintain the same growth rate as the fish that were fully fed daily. Growth was reduced by almost 50%, and the feed factor increased by about 130% compared to the control group.

At the end of the fasting period, the fish showed clear signs of energy balance disturbances, including low hepatosomatic index (HSI) and reduced levels of ghrelin (Ghrl), a hormone that stimulates appetite. At the same time, increased transcription levels of agrp1, a neuropeptide that acts as a glucose sensor and appetite stimulator, were observed. Changes in plasma levels of glucose, lactate, and cholesterol suggested a redistribution of energy sources.

Highlights

  • Six weeks of periodic fasting reduced growth and K-factor in Atlantic salmon.
  • After resuming feeding, the fish showed increased appetite (hyperphagia) and a tripling of stomach content.
  • Feed restriction altered appetite and hormonal signalling for energy balance in the fish.
  • Full refeeding resulted in similar growth, appetite, and hormonal signals as the control group.

No health damage, compensatory growth

Despite these changes, there were no indications that the fasting period had harmful effects on the fish. The metabolic adjustments allowed the salmon to continue growing, although the growth rate was reduced. After returning to daily feeding after six weeks, the fish showed a tendency for compensatory growth, and the differences in hormonal signals related to appetite regulation and energy balance were equalised compared to the control group.

This underscores the physiological plasticity of Atlantic salmon to adapt to temporary feed restrictions.

Potential for economic and ecological benefits

The feed saved over the 40 days of periodic fasting was estimated to constitute 35% of the full ration, and approximately 75% of normal feed was used after the salmon had fully adapted to the feeding regime.

According to the researchers, the results provide breeders with a new strategy to balance between cost savings and fish production. The results also provide new insights into the physiological mechanisms that occur during periodic fasting in Atlantic salmon, and demonstrate a feeding regime that can be applied in periods of limited feed availability or when breeders aim to achieve strategic growth goals in commercial production.

The researchers conclude that intermittent fasting can be an effective method during periods of limited feed availability or to achieve specific growth goals. At the same time, the study demonstrates the physiological plasticity of Atlantic salmon and their ability to adapt to temporary feed restrictions without health damage.