FISH FEEDING AND GROWTH
Types of feeds
In Europe, intensive aquaculture began at the end of the 19th century, when governments decided to breed fish to obtain fingerlings which were used to restock lakes and rivers (Polanco & Bjorndal 2018). Those fish represented an important source of protein for river communities, and helped to alleviate hunger. Efforts were made to promote the most appreciated species, such as salmonids, which are carnivorous. As production increased and fish were kept under intensive care for longer periods, farmers began to formulate feeds.
· Aqu@teachProximate composition of fish feeds and essential nutrients
When research began on fish feeds more than 50 years ago, scientists first analysed the natural diets of the species in question. Trout, as an example of a carnivorous fish, had a natural diet that consisted of 50% protein, 15% fat, 8% fibre, and 10% ash, which is high in protein compared to terrestrial mammals. Ever since then researchers have been trying to find the right balance of protein, carbohydrates, fats, fibre, vitamins and minerals for fish used in aquaculture (Bhilave et al.
· Aqu@teachProduction plan and monitoring the evolution of the farm
All aquaponic farms need well defined production goals and a plan to fulfil those goals. Specifically, it is helpful to define the following aspects well in advance: The species to be used The size of fingerlings needed initially and the target size of the adults to be sold at the end. This will help to define the productive cycles on the farm (types of tanks, etc.) The optimal densities and housing conditions for each stage of growth.
· Aqu@teachMain interactions between ingestion and environmental factors
As commented above, we should be able to house each species according to its requirements. For that we first need a profound knowledge of the species that we are going to work with before we begin to grow the fish or start the installation. Once we have this information, we should be able to maintain the adequate housing conditions in our system, which in this case is related to aquaponic systems.
· Aqu@teachGeneral introduction to fish feeding
Feeding and fish nutrition are fundamental aspects of aquaculture, both in terms of fish growth and in economic terms. Proper feeding depends on the development of quality feeds and on choosing appropriate methods to distribute the feed to the fish in the tanks. Apart from affecting growth, feeding can also affect fish health and welfare, which depends in turn on how much we know about the requirements of each species. Each species has its own natural history and well defined stages of growth, which should be understood in order to provide optimal care.
· Aqu@teachFeeding strategies
Apart from using adequate feeds, we need to ensure that the pellets provided are the right size for the mouth of the fish. For small fish this usually means a fine powder and for larger fish a round pellet that can be several mm in diameter. For example, Aquaponics USA suggests using powder for tilapia from hatching to 3 weeks old, and then a fingerling crumble (1/32 inch or 0.9 mm) until they grow to about 2 cm in length, fingerling pellet (1/16 inch or 1.
· Aqu@teachEnergy requirements
As with all living animals, fish require energy, and that energy is provided by the oxidation of the organic components in feed. Fish require energy to carry out their daily activities, such as breathing and swimming, and to transform, restore, and grow their body tissues. The energy requirements of fish depend on their physiological state and on the environmental conditions. In general fish make a more efficient use of the energy ingested compared to terrestrial mammals, due to the following reasons:
· Aqu@teachDesigning feeds for aquaponics
Fish feeds for aquaponics can be home-made or bought from specialized feed companies that formulate specific diets depending on the species and age of the fish. Normally commercial producers use specialized feeds since they are guaranteed to meet all the nutritional needs of the fish, and tend to be more cost effective compared to making and formulating one’s own feed. However, formulated feeds are not always perfect and may have varying effects on the quality of the water where fish live and excrete waste.
· Aqu@teachAutomatic feeders
The automation of feeding requires knowledge about the feeding habits of the species in question. We also need to know technical details, such as the number of fish in each tank and their sizes. Manual feeding has advantages, as mentioned above, and is still used to ‘keep in touch’ with the fish. Nonetheless, technological developments can facilitate this labour. Nowadays there are many types of automatic feeders, especially for large-scale projects with a large biomass.
· Aqu@teach