A. Fish Environment / Environmental Requirements

WATER MANAGEMENT

Water temperature

All fishes have upper and lower temperature tolerance limits. When the temperature goes beyond the temperature tolerance limit of the fish, the effects are:

• abnormal metabolism resulting in poor growth, abnormal activities or stress
• poor response to supplemental feeds
• very poor feed conversion ratio

An ordinary thermometer or an equivalent device can be used to measure water temperature.
Tilapia nilotica can tolerate water temperature range of 14° - 42°C. However, for culture purposes, the ideal water temperature should range from 25°C to 30°C.

Hydrogen ion (pH) Concentration. The pH of the water determines its acidity or alkalinity. If the pH is between 0-6.0, the water is acidic, and if the pH is 7.0, it is neutral. Alkaline water has a pH of 8.0 -14. The ideal pH range of freshwater culture is 6.5 - 9.0.
The effect of the various pH value on fish is shown below:

pH Range	Effect
4 and below	Fish die because of acidity
4 - 5	No reproduction
5 - 6.5	Slow growth because of low fish food production
6.5 - 9.0	Fish thrive well and grow fast
11 and above	Fish die because of alkalinity

Ammonia. This is highly toxic to fish. the symptoms of ammonia toxicity in the fish are:

• spongy appearance of gill filaments
• presence of bloody gills
• excessive production of slime
• poor growth of fish

Dissolved Oxygen. All fishes, regardless of species and culture conditions, need oxygen for growth and survival. Lack of oxygen results in poor growth and outbreak of diseases or mortality. Generally, most warm water species need dissolved oxygen at a level of one part per million (ppm) for survival and about 3 ppm for comfort. Dissolved oxygen of 5 ppm is the most ideal for growth and is excellent in maintaining fish health. However, tilapia species can grow well at dissolved oxygen level of 1 - 3 ppm

Good water management prevents the occurrence of dissolved oxygen depletion. In order to maintain high dissolved oxygen level in the pond, do the following:

• Prevent the growth of unnecessary aquatic vegetation, such as "kangkong" over the pond surface. These plants shield the pond from sunlight and slow down photosynthetic activities of phytoplankton to produce oxygen.
• Follow the recommended stocking rate of the pond. Over-stocking leads to high oxygen consumption and possible oxygen depletion especially at night.
• Avoid giving excess feeds to the fish since unconsumed feeds pollute the pond water when they sink to the bottom and decay.

Some of the signs manifested by fish due to dissolved oxygen depletion in ponds are:

• Restlessness associated with abnormal closing or opening of the operculum.
• Gasping for air at the water surface
• The pond water becomes brownish to grayish and smells pungent

Turbidity. The presence or suspended solids in the water causes turbidity and muddiness of the water. Generally, suspended solids include sediment particles, organic matter like detritus, fecal materials and phytoplankton. Turbidity can be either an advantage or a disadvantage in fish culture. It is advantageous if it is caused by plankton. However, if the water is turbid due to minute solid particles, then this becomes a disadvantage because the sediment particles prevent photosynthesis. Turbid water has the following effects:

• suspended solids clog the gills of the fish or cause irritation on the gill filaments.
• heavy minute particles can bury eggs and larvae of organisms that live in the pond bottom.