PRINCIPLES OF POND FISH CULTURE
1. Fish are dependent for food directly or indirectly on plants.
2. The weight of fish which can be produced in natural waters is dependent upon the ability of the water to raise the plants. We could increase production by adding plant organic matter produced elsewhere.
3. The ability of water to produce plants is dependent upon sunshine, temperature, CO2, Mineral from soil or rocks, nitrogen (NO3- and NH4-) , O2 and water.
4. The Natural fertility of the water is dependent on the fertility of the soil in pond bottom and watershed.
5. Fertlity of water can be increased by adding inorganic fertilizers.
6. After adding all essential minerals and all available nitrogen, the next limiting factor is CO2. This compound can be increased by adding organic matter followed by liming (Ca, Mg).
7. The next limiting factor in fish production, after mineral and CO2 are provided, is oxygen demand of all living and dead organisms in the water. This can be supplied by running water rich in oxygen or pumping water from the bottom and aerate it. If oxygen in the water falls below 1.0 ppm, fish die. One ppm oxygen is enough for fish in resting condition, but for active fish, 3.0 ppm is needed.
8. Microscopic plants (planktonic algae) are the principal food producing plants for fishes.
9. Microscopic plants are the most desirable, because : (a) short life cycle, (b) mobility, (c) more nutritious, and (d) small size.
10. Rooted plants are less desirable, because: (a) long life, (b) immobility, (c) less nutritious, (d) large size, and (e) shading effect.
11. a. The more fertile the water the heavier the plankton concetration becomes, the more shallow becomes light penetration and photosynthesis.
b. Heavy plankton concetration in top water causes shallow stratification and low oxygen or none in deeper water. Strong wind, or heavy cold rain causes overtum, causing trouble to the fish. Water with no oxygen spread too fast and could kill the fish. Heavy plankton can be killed by the use of CuSO4. Light can penetrate deeper, so does the production of oxygen.
c. the deeper the fertile lake or pond (heavy plankton) the higher the precentage of the total volume of water deficient of oxygen during period of stratification.
12. Rooted plants are desitable, in part, in waters of low fertility, because : (1) Oxygenate deep water as far down and light penetrates, (2) draw nutrients from pond bottom soil, (3) prevent marginal erosion, (4) provide surface for food organisms, and (5) provide food for fish derectly or indirectly.
13. The longer the food chain from plant to fish the lower the production of fish obtained. The conversion rate from:
Plant to fish = 5 – 10
Plant to insect = 5 – 10
Insect to fish = 3 – 10
fish to fish = 2 – 5
14. At a given level of fertility the fish production is constant for a particular species and a certain rate of stocking. The total pound/acre is dependent upon the number of fish present and the size harvested. Small fish produce high number of lbs/acre, and large ones produce small number of lbs/acre.
15. For short period of time we can regulate number ( and final size) by the number stocked. This can be done by frequent draining before the fish are old enough to spawn. For non spawner there would be no difficulity. Mortality rate can be up to 20 percent a year.
16. For long period of time the number of fish and sizes must be controlled by biological methods such as:
1. Repression - prevents reproduction, e.g. carp.
2. Predation - method of controlling the number of young fish.
3. Starvation - this could lead to weakning of fish, thus vulnerable to disease and parasites.
4. Limited spawing area
17. The greatest total weight to any one forage species (for short periode of time for piscivorous fish) can be produced in waters containing only that species.
18. The greatest total weight of fish can be produced by combination of forage fish differing in feeding habits.
19. The presence of piscivorous species decreases the total weight or fish, decreases the number of fish, but increases the average size.
20. The rate of feeding required to maintain a fish is less than the rate required for growth.
21. The amount of food required to maintain one-pound fish for one year is equal to the feed required to raise the fish to one pound.
22. A population of fish at a given level of food abundance will tend to expand until harvestable food equals the amount required for maintenance.
23. Feeding at maintenance is uneconomical for extended periods. Feeding to satiety is uneconomical too. Econimical feeding rate varies with the size of fish.
24. Economical feeding rate per acre is limited by the eficiency of the ecological system in waste disposal and reoxygenation.
25. High quality feeds must contain in proper proportion; protein for building fish flesh carbohydrate and fat for energy, minerals for contruction and regulation, and vitamins for regulation of life processes.
26. Quality of feed influences (a) the amount of waste, (b) health of fish, and (c) rate of growth.
27. By increasing feeding rate the stocking rate of fish can be increased. This could increase the incidence of parasites and diseases.
28. Within limits regulation of feeding rates can replace predation in obtaining a high percentage of harvestable fish.
29. Rates of growth of fish vary widely and are dependent upon : (a) their ability to grow, (b) the quality of feed, (c) space – waste disposal system, (d) temperature, (e) the amount of feed per individual.
30. Minimum age at spawning is dependent upon rate of growth.