Fish Feed Production from Local Feedstuffs
written by: Ozochima Victor Chima
By 1993 it was becoming clearer that fishing from the wild
cannot sustain fisheries needs in Nigeria. Inland aquaculture
in Nigeria produced 15, 576 metric tons with per capita availability
of 5 kg of fish compared with per capita fish supply of 25.4 kg and 7.7k g for
developed and developing countries, respectively (Coche et al.,
1994). Hence, Nigeria had become a net importer of
fish. With the structural Adjustment Programme (SAP) and the devaluation of the
Naira, fish importation declined. By 2001 the aquaculture production
in Nigeria was only 24,395 metric tons (FAO,
2003). There was thus increasing pressure on aquacultural
products. Aquaculture production depends to a major production of
adequate artificial feed for fish. Feed represents the single most
expensive production cost in aquaculture operations (Shang, 1981) comprising
over 50% of the running costs. It therefore needs adequate attention
if aquaculture has to succeed.
In
terms of nutrition, fish can be broadly grouped into, carnivores for fish that
feed on other animals, herbivores for those that feed on algae and other plants
and omnivorous for those that feed on plant and animal materials. The feeding
habit of fish is usually considered when producing feed for the species. Again,
larval fish are fed differently compared to other fish. Feed
production is to as far as possible, take care of the gastronomic habits of the
target fish. This is done by preparing feeds that meet the specific
nutritional and physical property needs of the fish. The production has to
recognize the slow feeder, the fast feeder, surface feeder, mid water feeder
and bottom feeder.
Below are terms used in nutrition of most cultured fish.
1. Fish
feed is that material given singly or in combination to fish which may
not be necessarily what it consumes in nature.
2. Fish
food on the other hand, is the edible material which fish choices to
consume in its natural environment to furnish nutrients to the animal. At
times, however, the term fish food is used to include both prepared diets and
natural nutrients. We will stick with the first definition.
3. A diet is
any substances prepared as nutritional substitute for fish food.
4. A nutrient is
a dietary constituent of feed or food that aids in the growth and the support
of life processes.
5. Ration is
a 24-hour diet allowance for the animal. A material or mixture of
materials to make an
allowance for 24 hours.
Some principles to be considered in aquaculture include:
1. Fish
is poikilothermic i.e. cold-blooded animals and its energy of metabolism
differs from those of homoeothermic (warm-blooded) animals. Fish
does not need as much energy for metabolism. Commercial diets used for some
important species of fish such as channel catfish for grow-out purposes as a
result usually contain 32% crude protein and 3.0 kcal digestible energy (DE)/g
of diet, for a digestible energy : protein ratio (DE/P) of 9.4 kcal/g of
protein (Reis et al., 1989).
2. Carbohydrate
is more poorly digested in most fish than in land animals. A
lot of carbohydrates feed is excreted. Recent research,
however, have shown that Clarias spp. efficiently utilize
non-protein energy from carbohydrates and can improve protein retention (Luquet
and Moreau, 1990).
3. In
protein metabolism nitrogen is excreted by most fish as free NH3 in
water. About 80% of excess nitrogen is excreted as NH3. In
terrestrial animals, excess nitrogen is excreted in urine and this process
requires energy. The nitrogen is excreted as urea and hence a loss
to the animal in the form of carbon, oxygen and hydrogen which are excreted
with every molecule of nitrogen. Fish is therefore more efficient in
excretion of nitrogen needing less energy and wasting fewer materials.
4. There
is no danger of overfeeding in land animals. Over feeding in fish
affects the water quality. Floating feed is an advantage in pond
feeding, though slightly more expensive than sinking pellets, because the fish
can be seen feeding and how much feed to offer to the fish without wastes can
therefore easily be determined (Mgbenka and Lovell, 1984).
5. Fish
absorbs dissolved nutrients such as Ca++, out of the water. Inorganic
phosphates (PO42-) are not much found in
water. Phosphorus is bound up in the bottom mud hence the need to
fertilize ponds especially when the secchi disc visibility exceeds ≥ 45
cm. Most organic and inorganic materials are picked up across the gills
into the blood stream. Nutrients which are not picked up or
manufactured by fish at all or insufficient quantities in culture condition are
supplemented in the feed e.g. vitamins and minerals.
6. For
a high percent crude protein diet we require high percentage of protein
supplement feedstuff in the finished diet and vice versa for low percent crude
protein diet.
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