By: Dr Mustapha ABA, Aquaculture Researcher, Fish Nutrition. Morocco.
The development of fish farming is based on the establishment of appropriate feeding and a management strategy that is based on the identification of daily feeding patterns or rhythms. It is well known that the amount and timing of feeding plays an important role in the performance and efficiency of feed use. Optimal feeding is important not only to regulate feed intake, growth and chemical composition of the fish, but also to prevent deterioration of water quality resulting from overfeeding.
Nutrition is one of the most important factors influencing the performance of farmed fish and is influenced by factors such as fish behaviour, stocking density, feed quality, daily ration size, feeding frequency and water temperature. Feeding frequency depends mainly on the species being farmed, age, size, feed quality and environmental factors. Determining the optimal ration and feeding frequency are important elements for the aquaculture operation, as they are important to ensure a feed conversion rate (FCR) of the cultured organism and to avoid pollution of the aquatic environment.
Good feeding practice is the provision of cost-effective feed at the right time(s), in the right quantities and in the right form for optimal fish growth. Both over-feeding and under-feeding can be detrimental to fish production. Over-feeding can lead to a marked deterioration in water quality (decrease in dissolved oxygen and increase in ammonia content), reduced growth/feed utilization and increased susceptibility to infections (due to increased susceptibility to infectious diseases through stress due to poor water quality).
For this reason, feed management in terms of optimisation (feed rate and frequency) has become a crucial area of study in the culture of many aquaculture species.
Ration Level and Feeding Frequency
Fish feeding response and feed utilization can be greatly influenced by the stage of biological development of the fish and the time of day when they feed, as significant mortality can result from poor feeding practices at different stages of fish development. On the other hand, over-feeding can overload the stomach and intestine, leading to reduced digestive efficiency and reduced feed utilisation. The results are increased conversion rates and environmental pollution. Since fish fry absorb a high daily feed ration to meet their nutritional requirements and therefore ingest an adequate amount of food, and since high feeding frequency results in a high daily feed ratio and small amounts of food per feeding, in this case a higher frequency can only be the most adequate.
However, the success of aquaculture depends to a large extent on good management of the frequency of feeding of fish fry (the number of times per day that fish fry are fed) which may not be economical due to increased labour costs. However, one of the goals of fish farmers is to constantly seek a good balance between fish growth and feed consumption. The production of high quality fish fry is one of the key factors in the sustainable growth of the aquaculture industry.
Carnivorous species may have a lower frequency of omnivores and, depending on the age of the fish fry, the higher frequency of feed for the fry can provide significant benefits to its growth. Adequate feeding frequency can lead to the lowest variation in the size of fish fry, which has a major impact on their trade.
High productivity requires proper feed management, with the use of nutritionally balanced rations, which account for 40-60% of total production costs. In addition, in aquaculture businesses where maximum growth is desired, as well as the reduction of production costs and environmental impacts, an adequate feed management protocol is necessary.
Factors influencing feeding frequency
Adequate feeding frequency stimulates fish to forage for food at predetermined times and helps to improve feed conversion, increase weight gain, reduce feed waste and production costs, provide better water quality in farmed water, and provide more opportunities to observe fish health status through changes in feeding activity. The frequency of feeding required for proper fish development varies mainly according to species, age of the animals, water quality and temperature.
Feeding frequency varies with age, fish species and water quality, especially oxygen level and temperature.
Fish metabolism varies with water temperature. When the temperature decreases, the appetite of the fish also decreases; when it increases, the appetite of the fish increases. The factors influencing the level and frequency of feeding are described below
- Dissolved oxygen levels also interfere directly with the feeding of fish fry. Oxygen levels below 5mg/L already begin to interfere with appetite, as fish stop eating when they are below 3mg/L. Often fish do not feed in the morning because oxygen levels are low, returning to the diet only after these levels are increased. Monitoring dissolved oxygen levels is an essential management measure for fish farming.
- Feeding frequency decreases as the age of the fish increases. Small fish should be fed several times a day to support their development. A feeding frequency of several times a day promotes better feed conversion in the fish compared to an average of two to three times a day. The feeding frequency of fish fry is higher than that of larger fish, as the latter have a greater capacity to store food in the stomach.
- Feeding schedule: This is a variable that is also related to the fish species. Omnivorous fish feed best in the early morning and at dusk, but can adapt to other times of the day. Ideally, fish fry should be fed at the same time to condition them.
- Feed Supply: In the first two weeks when the fry arrive from the hatchery, feed should be spread over the entire surface of the tanks so that each fry has the opportunity to feed. At this stage, there is marked social segregation and, if feed is not provided uniformly, uneven growth of the fry group occurs, resulting in increased differences in size and weight and subsequently a non-homogenous population.
Maintaining good management of the level and frequency of feeding of finfish fry in aquaculture can bring positive results in terms of productive performance, a fact that would certainly have a positive influence on economic performance. Better optimization of feeding frequency can lead to the desired results for the aquaculturist while minimizing costs and avoiding over-feeding that could adversely affect water quality.