Monday, February 11, 2019

Seasonal nutrition: Matching fish feed to fish physiology

by Dr Robert Tillner, Product Manager, Aller Aqua Research, Germany

In most areas in the world, nature follows seasonality in one way or another. This affects both physiology and behaviour of animals, across different genera. As many fish species are poikilothermic, their internal temperature varies considerably, as a result of fluctuations in the ambient environmental temperature.

In a changing climate, this dependency can have a severe impact on natural and captive fish populations, when rapid drops or rises in environmental temperatures occur, occasionally over a short period of time.

The temperature/metabolism connection
The variations in body temperature have a pronounced impact on both the speed and efficiency of fish metabolism. In this respect, fish metabolism is increased in higher temperatures and vice versa. Consequently, the feed intake, as well as nutrient digestibility and nutrient utilisation of fish, vary with temperature.

When the seasons change from winter to spring, a rapid change in water temperature occurs on many fish farms. This is considered the most delicate period in fish farming. The drastic temperature increase affects the metabolism of fish and challenges its immune system. Often, the difficulties fish experience in adjusting to a changing environment become noticeable as poor appetite, apathy and skin lesions.

Consequently, fish having problems with changing environmental conditions show reduced growth performance, which results in less profit for farmers. This contrasts with changing farm operations in the transition from winter to spring as feeding intensity increases.

Warming temperatures boost metabolism
When water temperature rises, fish show a reduced capacity to resorb oxygen from the warmer water, as oxygen solubility in water decreases with rising water temperature. This is especially true for juvenile fish, as they are more susceptible to oxygen deficiencies, compared to adult fish.

To cope with these conditions fish, by nature, have a generally high ability to exploit oxygen from the water. Therefore, sudden increases in water temperature might become a stressful factor, especially under more intensive farm conditions when extra oxygen supply is limited, or its application is too costly. Physiologically, fish adapt to sudden changes in temperature by increased respiration and higher levels of stress hormones in their blood.

It is therefore paramount to support the fish organism in this potentially stressful period, by using specific nutrients in the feed. Most animals can synthesise vitamin C, but many fish cannot. Physiologically, vitamin C is the precursor of collagen and is, therefore, necessary for the formation of connective tissue, scar tissue in wound repair and bone matrix. It also facilitates the absorption of iron and protects tissue from oxidative damage. An increased immune response, due to high concentrations of vitamin C supplementation, has been documented in many fish species.

The Spring Edition feeds from Aller Aqua contain an extra dose of vitamin C, which contributes to the formation of red blood cells and promotes the production of collagen, thus facilitating the intake of oxygen and promoting the healing of the skin and the healing of wounds. Ultimately, it supports the fish during the challenging transition period from winter to spring.

Read more HERE.

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