Good nutrition in animal production systems e.g. fish nutrition is essential to economically produce a healthy, high quality product. In fish farming, nutrition is critical because feed represents 40-50% of the production costs.

Fish nutrition has advanced dramatically in recent years with the development of new, balanced commercial diets that promote optimal fish growth and health.

The development of new species-specific diet formulations supports the aquaculture (fish farming) industry as it expands to satisfy increasing demand for affordable, safe, and high-quality fish seafood products.

What is Fish Feed?

To consider what a living animal needs to feed on, the first thing that comes to mind is to cover the energy requirements in order to ensure the basic vital functions (moving, growing, reproduction and metabolism). The energy for these is provided by the intake and uptake (metabolism) of the proteins, fats (lipids) and carbohydrates contained in the food.

Also, the animal needs a certain number of substances to be able to grow and function properly: for example, vitamins and minerals that have a secondary but essential role in the body.

In this respect, fish are not so different from other animals, needing to eat to be able to live, grow and reproduce.

However, farmed fish are a bit special when compared to other farmed animals because most of farmed fish species in Western Europe are highly carnivorous (salmon, trout, sea bass, sea bream, turbot…).

They therefore need a high level of proteins in their diets. Feed manufacturers have a common goal – to produce feeds that are nutritious, easy to handle and economically
acceptable in the production chain. If these criteria are met, this allows the production of affordable, high quality fish for the consumer.

Supplementary Diets

Two concept of supplementary diet have recently been recognized. One school of thought defines it as a supplement fed along with another one. While another school of thought regards it as one fed to supplement the natural food present in the environment.

The latter definition was accepted and adopted by aquaculture experts. Feed industries are characterized by constant fluctuation in the prices of feed ingredients.

This is practically due to the seasonality of most of these feedstuffs and also because of several alternative uses of the ingredients especially in poultry and livestock industries, and even for human consumption.

These shortcomings have thus necessitated the use of alternative feed ingredient for possible inclusion in the diet of farmed fish and as a total replacement for fishmeal where possible. It is however note worthy that in finding a replacement, the aim of producing a high quality food (fish) for humans’ consumption that is environmentally friendly, cost effective and that is sustainable must not be compromised.

These occurrences have been traced to the presence of elements within vegetable meals that inhibit nutrition of fish species. These elements, called antinutritional factors have the potential of precipitating adverse affect on the productivity of farm livestock including fish and are found present in the foliage and /or seeds of virtually every legume plant that is used in practical feeding.

In the quest to find alternative protein sources using locally available materials in fish feed preparations, much attempts and successes have been recorded. It has however been pointed that, most of the feed ingredients have not performed credibly well in terms of their protein digestibility and biological value to fish when tested as replacer for fish meal.

With the unequal position occupied by fishmeal as “ chief protein source” due to its balanced amino acids composition in the diet of fish and livestock it therefore become a better practice that a vegetable protein be made to replace another one in practical fish fed formulation.

Fish Meal as a Component of Fish Feed

For the production of high quality fish most of the fish species farmed around the world including catfish that is popular in Nigeria are essentially omnivorous and carnivorous, their metabolism requires access to fish or fish materials in their feed. So, fish meal is composed of the following materials.

1. Fish Meal

Fishmeal is a high protein feedstuff often included in poultry diets. It is usually marketed at 65% crude protein, but the crude protein content can vary from 57 to 77%, depending on the species of fish used.

Several species of fish can be processed into fishmeal, but the most common are Anchovy and Menhaden. Major fishmeal producing countries are Chile, Norway, Denmark and Peru.

Most fish species can not be harvested year-round. As a result, there is seasonal variation in protein content, depending on the species of fish used. The crude protein content of fishmeal is usually highest during the Menhaden harvest. The price of fishmeal varies throughout the year and is a reflection of the seasonal variation in the supply of fish. The price of fishmeal is usually the highest during the winter months when the supply is lowest.

The price also varies from year to year depending on the price of other protein sources, in particular soybean and other oil meals. Fish meal coming from pelagic fish, which are the most used to supply fish oil and fish meal. Generally, these fish species are unsuitable for human consumption because they are small and bony and it wouldnot be economically viable to process them into products adapted to consumer needs.

To cover all the dietary requirements of carnivorous fish, the feed must be high in energy content. This means it has to be protein rich (from 38% to 45% according to the need of each species). It also has to be of good quality, must be highly digestible and have amino acid profiles adapted to the nutritional requirement of the fish species in question.

2. Fish Oil

Fish oil is also obtainable from pelagic fish. Apart from the essential proteins, the food must also cover the particular requirements for oils. Key requirements are the healthy Omega 3 and Omega 6 poly-unsaturated fatty acids: these control vital life processes including
reproduction, physical development (especially of the brain and the nervous system), immunity, inflammatory processes and a healthy cardiovascular system.

Pigment such as Astaxanthin, a naturally-occurring carotenoids pigment that is a powerful biological antioxidant but is also essential for protection against UV-light effects and stimulating the immune response. Wild fish get this natural pigment from eating tiny crustaceans.

3. Vitamins

Vitamins A, C, D and E, the B group and others, such as biotin Minerals such as calcium, phosphorus and other essential trace elements are readily available in fish meal. Similarly, vegetable products such as cereals, soybean, glutens and vegetable proteins are increasingly used in modern fish feeds as some of these have been found to contain some of these mineral element and vitamins.

A lot of research work has shown that vegetable sources of protein (soy, pea, sunflower) and oils (soy, colza, linen) are perfectly usable in varying proportions in fish feed. At the present time, fish meals and oils represent around 50% or less of certain formulations. In the near future, their percentage will be reduced even further.

4. Moisture

The moisture content of fishmeal is normally low in order to facilitate storage and transport. If the moisture content remains at the acceptable lower limits the meal will be more likely to have a low bacterial and/or mold count.

Antioxidants must be added to the meal to ensure proper stabilization during extended periods of storage. Fishmeal contains three major nutrients; protein, fat, energy and minerals (ash).

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