By : Dr Mustapha. A. Aquaculture Scientific Expert in Fish Nutrition. Morocco.
To a large extent, water determines the success or failure of an aquaculture operation. Water quality is a dynamic network of physical, biological and chemical factors that influence fish production. The most important water quality parameter is temperature. It is a key abiotic factor as it affects all the metabolic and physiological activities of the fish; the nutrition, growth, reproduction and behaviour of the fish, in this context the aquaculturist must take measures during the winter season, in order to avoid losses in aquaculture.
Changes in ambient temperature have a crucial influence on aquatic animals such as fish which are poikilothermic (or ectothermic) animals whose body temperature varies with the ambient temperature. However, each species has an appropriate range of tolerance limits, when the ambient temperature is too hot or too cold to exceed the limit, the health of the aquatic animals is affected which may result in the death of the aquatic animals. In general, when the temperature is low, fish growth is hindered due to reduced metabolic activity, fish eat less, fish growth rate is slow, as they move less, depending on the temperature, they can reach death in extreme cases.
As fish are cold-blooded aquatic animals, they require special care in winter, so it is essential that the fish farmer takes certain measures to adapt the management of aquatic animal feed to lower temperatures, in order to ensure the health and greater efficiency of the entire system during this critical season of the year.
Water temperature and fish
Fish do not regulate their body temperature, unlike mammals and birds, they are animals whose body temperature is the same as that of the water in which they are found, whether in the open or in captivity. The vast majority of fish regulate their metabolism according to the temperature of the water they are in, which can be accelerated if the temperature rises, or decreased if the temperature drops. During this winter season when the ambient temperature begins to drop, the water temperature also drops to levels considered uncomfortable for the fish. The biggest consequence of the cold is the decrease in metabolism, which causes fish to reduce their need to move around and feed, as their metabolic processes, such as respiration, digestion and excretion decrease. As a result, fish are less hungry and feed less frequently or even stop feeding. In aquaculture, this fasting is harmful to fish farmers because it slows down or stops the growth of the fish.
Aquaculture management and water temperature
In high altitude areas, in winter and spring, it is cold and the water temperature is often very low. On the other hand, when the water temperature is low, fish and other sedentary aquatic animals often congregate at the bottom of the pond where the temperature is higher than the upper water layers. During the winter, various fungal, bacterial and parasitic diseases such as fin rot, gill rot and argulose can appear in fish. In addition, as day length and light intensity also decrease in winter, oxygen levels in fish ponds decrease due to reduced photosynthetic activity. The situation becomes even worse on continuously cloudy days.
For growing tanks or small ponds, a frame can be erected and covered with plastic to seal the space above the water surface; this solution, although inexpensive, avoids heat loss and creates a greenhouse effect that stores heat for the aquatic environment of the pond. For water ponds, which are maintained with a high density of spawners or aquatic species of high economic value, warm aeration can be chosen. This method adds both oxygen and heat to the aquatic environment, or the use of water heating to increase the ambient water temperature in fish rearing ponds.
Aquaculture winter feed management
In the field of aquaculture, prevention is the most effective way to avoid winter-related problems. In addition, management practices must be planned in advance. In addition to water temperature management solutions, aquaculturists must take advantage of warm, sunny days to ensure that aquatic animals eat sufficient nutrients, and at the same time add nutritional factors that contribute to increasing resistance such as vitamin C, and E .
The demand for food consumption by aquatic animals during the cold season is lower than during the warm season, so fish farmers must take precautions by using highly digestible protein-rich feeds to avoid high nitrogen excretion, as fish are subject to another challenge in addition to temperature, which is the reduction of protein digestibility, due to a low metabolism, so overfeeding fish should be avoided, as this will be an economic loss, avoiding overfeeding, as it leads to environmental pollution and affects fish resistance.
Water temperature is an important variable in aquaculture, but in most types of aquaculture it cannot be controlled, in order to allow the different species of fish to better cope with the challenges posed by changes in environmental temperature during the winter, it is therefore essential that the fish farmer takes certain measures to adapt the management of aquatic animals to low temperatures, in order to guarantee the health of the fish, through better optimisation of feed consumption due to the reduced activity of the fish metabolism, to avoid the wastage of feed in the environment.