Warmer water leads to inhibited fish growth, a study has shown.

Warm water and low oxygen inhibit fish growth

Work by a Norwegian researcher has investigated how the appetite and growth of salmon is affected by low oxygen (hypoxia) and high temperature, a challenging environmental mix expected to increase because of global warming.

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Vibeke Vikeså also looked at the effect of high energy levels in the feed as part of a doctoral study.

Four feeding experiments were carried out with salmon in sea water at various temperatures (12-13 °C versus 17-19 °C), with two of the tests including low dissolved oxygen levels.

The experiments showed that high temperature reduces appetite and growth, even under favourable oxygen conditions. Impaired growth potential at high temperatures was evident from limited salmon weight gain, utilisation of nutrients and hormonal regulation of growth. Low oxygen resulted in higher metabolic demands, which causes a further growth reduction at both optimal and high temperatures. High-energy feed had a positive effect on both growth and energy metabolism.

Vibeke Vikesa saw lower growth in salmon faced with higher water temperatures and lower oxygen levels. Picture: Skretting

In the abstract to one of three articles that comprise her thesis, Vikeså writes: “Pair-feeding of rations based on the feed intake of the low oxygen groups, but fed at high oxygen, resulted in a 50 per cent growth improvement in high energy (HE) diet groups. This suggests that the poor growth under low oxygen was not entirely caused by the reduced feed intake.”

Increased muscle growth

She continues: “Growth regulation was affected by the HE diet, with increased liver and muscle growth hormone receptor ghr1 mRNA (p < .05), regardless of oxygen level. The growth depression due to low oxygen appears to be related to higher metabolic costs, while higher dietary digestible energy levels (high vs. low) upregulates the GH-IGF system at the ghr1 level and [is] found to be beneficial for growth, feed intake, oxyregulation and osmoregulation under hypoxia.”

Diet effects and environmental effects on growth are of great interest for salmon farming, as more knowledge can contribute to increased growth, welfare, health, reduced environmental impact and thereby future breeding opportunities.

Vikeså gained an aquaculture degree from the Department of Fisheries and Marine Biology, University of Bergen (UiB), in 2001. Her doctoral research work has been a collaboration between the Norwegian Institute of Nutrition and Seafood Research (NIFES), the University of Bergen and Skretting Aquaculture Research Centre (ARC). Supervisors have been Professor Rune Waagbø NIFES / Bergen, Dr Ernst Morten Hevrøy of EWOS Cargill (formerly NIFES) and Dr Leo Nankervis, Skretting ARC. Vikesaa works as a researcher at Skretting ARC in Stavanger.

Appetite, metabolism and growth regulation in Atlantic salmon (Salmo salar L.) exposed to hypoxia at elevated seawater temperature:  http://onlinelibrary.wiley.com/doi/10.1111/are.13229/abstract

High dietary energy level stimulates growth hormone receptor and feed utilisation in large Atlantic salmon (Salmo salar L.) under hypoxic conditions:

http://onlinelibrary.wiley.com/doi/10.1111/anu.12488/full