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.
Countering stress from high temperatures
The summer period is characterised by high temperatures and the highest fish metabolism. Heat waves, and subsequent high-water temperatures during summer, challenge the fish when it comes close to the physiological boundaries of the animals.
Consequently, the summer season can lead to oxidative stress in the fish caused by a combination of high temperature and an intensified fish metabolism. Oxidative stress is an imbalance between oxidising substances and antioxidants, in favour of those oxidising, resulting in damaged body cells.
To maintain homeostasis, the body cells take up more energy to counteract oxidative stress. Symptoms in fish include heat stress, reduced appetite, weakened immune defence and a low quality of fish meat.
To counteract these symptoms the Summer Edition feeds from Aller Aqua are supplemented with natural antioxidant substances to restore oxidative balance. Antioxidants have several positive effects including reduction of heat stress, stimulation of the immune system, increased feed intake and consequently increased body weight.
With dropping water temperatures in autumn, fish metabolism slows down and the fish reduce their feed intake. Warm water fish species stop feed ingestion and prepare for a wintering period without feeding. It is therefore paramount to equip the organism with necessary energy stores and to support cellular functionality at low temperatures.
Preconditioning for winter
The membranes of all animal and plant cells are formed by membrane lipids of the main groups glycolipids, cholesterin and phospholipids, which build the typical membrane layer necessary for all life. In low temperatures, the fluidity of cell membranes is reduced if not supplied with phospholipids high in highly unsaturated fatty acids, leading to reduced exchange of water, gases and proteins.
The Autumn Edition feeds from Aller Aqua are equipped with high levels of phospholipids, which promote high digestibility of the feeds and secure the preconditioning for the wintering period. The supply of phospholipids supports the fluidity of the cell membranes and avoids solidification at low temperatures, which ensures optimal cell functionality.
Efficient nutrient uptake during the coldest season
At low temperatures, during winter, the feed intake is reduced and so is the metabolism of the fish. As a result, nutrients from the feed are poorly utilised and might be wasted, which is an inefficient use of precious feed ingredients.
During the winter season, feed digestibility can be increased by using emulsifiers which improve the digestion and nutrient uptake of dietary lipids. This is what Aller Aqua have done in their Winter Edition feeds. The lipids in the feeds are efficiently used and not excreted into the environment.
This can easily be observed by less or no fat films on the water surface, and on equipment on a fish farm. Consequently, the increased and faster availability of energy favours the growth of fish even at low water temperatures. Another challenge is the reduction in protein digestibility, due to low metabolism. This challenge is met with the addition of highly-available peptides. In the feeds, the peptides increase the digestibility of the protein fraction and the availability of amino acids.
Coming from the other end, the absorption of nutrients, by epithelial cells in the intestine, is an energy consuming process. The addition of highly available energy sources activates the epithelial cells which increase the reaction surface in the intestine and ultimately improves nutrient absorption.
In conclusion, adapting fish feeds to seasonal temperature differences on a fish farm creates a great potential for growth, vitality and health of fish and has become a core principle in Aller Aqua"s feed formulation. Therefore, Aller Aqua introduced the Temperature Adapted Feeds concept (TAF), ensuring a higher feed intake and nutrient digestibility throughout all seasons.
This is achieved by adapting nutrient contents in the feeds, to allow different fish species to better face the challenges of changing environmental temperatures, during the year. At the same time, it keeps nutrient excretion to the environment at a minimum.
The Temperature Adapted Feeds concept covers the four seasons of the year and a great variety of fish species, as new species are continually included in this principle.
Temperature Adapted Feeds for different species and seasons are developed in collaboration with international research institutes, fish farms and Aller Aqua Research. It is the result of Aller Aqua"s more than 50 years of experience in the fish feed industry, covering feeds for more than 30 species.
