Question

Short note about to become afish feeder in life

Answer 1

Explanation:

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Natural fish foods present in a fish pond are very diverse and usually consist of a complex mixture of plants and animals.

(a) They range from microscopic to relatively large size.

(b) They may be alive or dead (detritus) and available from bacterial decomposition.

(c) They are generally present in various parts of the pond:

near the shore such as rooted high plants;

floating in the water such as plankton;

on the surface of or within the bottom (benthic material or benthos*) such as worms, insect larvae and snails;

covering the surface of submerged objects (biological cover or autwuchs*);

swimming around such as aquatic insects, frogs and fish (nekton*).

2. To help you manage your pond through fertilization (see Chapter 6), you should learn to recognize the most important groups of natural fish foods. For this you will need a simple microscope (see also Section 15.3), which you might be able to find in a local health centre, school or in a fish-fry production centre. Ask your extension agent for advice. Look at the following pictures remember that some of these organisms can be very small and practically invisible to the naked eye.

Note: 1 micrometre (micron)= 1�m = 0.001 mm.

Phytoplankton

Zooplankton

Which natural food do fish prefer

3. The food preferred by fish varies considerably, depending on species and development stage.

4. As you have already learned, fish larvae do not actively feed but survive on reserve food in their yolk sac (see Section 9.4). A short time before the yolk sac is absorbed, early fry start eating natural foods, which usually consist first of the smallest plankton such as microscopic algae and rotifers. As their mouth size increases, the fry eat increasingly larger plankton (cladoceres/copepods) and insect larvae/pupae. Little by little, as the fry grow older, food preferences change to resemble more and more those of adult fish.

First month of feeding for common carp

TABLE 27

Natural feeding habits of adult fish

5. Adult fish belong to different categories according to their feeding preferences, as illustrated in Table 27.

(a) Herbivores prefer plant materials such as:

phytoplankton*, for example the Chinese silver carp;

higher plants, for example Tilapia rendalli, grass carp, and the Asian cyprinid Puntius.

(b) Omnivores eat a mixture of various natural foods, although most of them have preferences for certain foods such as:

zooplankton*, for example the Chinese bighead carp;

bottom fauna, for example common carp;

bottom detritus for example mrigal, an Indian cyprinid;

phytoplankton, for example the Nile tilapia;

fruits and seeds, for example the South American Colossoma.

(c) Carnivores prefer animal food such as insects, tadpoles, frogs and smaller fish, for example trout and catfishes such as African Clarias and Asian Pangasius.

6. You should ensure that there is a good supply of the type of natural food your particular fish species prefers. Phytoplankton organisms are the easiest to produce using a good fertilization programme (see Chapter 6). Zooplankton will then develop rapidly in the presence of algae to graze upon.

7. If you want to encourage the growth of biological cover, a mixture of minute surface-attached plants and animals, in nursery ponds, you can fertilize the water and use bundles of dried grass or crop stems fixed underwater.

Checking on phytoplankton

8. If your fish are phytoplankton feeders, it is particularly important to control regularly both the quality and the quantity available.

9. To check on quality, slowly pull a phytoplankton net (see paragraphs 12 to 15) across the pond in one direction. Try to cover a large area of water. Determine which types of algae are present with the help of a simple microscope (see Section 15.3). There should not be too many filamentous algae.

10. To check on quantity, estimate water transparency either with a Secchi disk or with your arm (see Section 2.3). The abundance of plankton is good as long as the transparency is less than 60 cm (see Section 6.0).