Poor and reduced growth

Health of fish is the major reason for poor and reduced growth. Maintenance of good fish health is critical to profitable fish culture. Slow growth, poor feed conversion, low yields, increased disease incidence and mortality, consequently low profitability are the results of poor fish health. Physiological stress is the fundamental cause of most fish health problems. The best way to manage fish health is through prevention. Practical health management is based on stress management. This involves preventing and minimizing stress to the fish in the culture environment.

Stress is an abnormal physiological condition of fish that results when the fishs collective adaptive responses to environmental factors are extended to, or approach its limit of tolerance. When fish are stressed, or continuously exposed to stress, their immune system becomes weakened. Consequently, their ability to fight disease is reduced and they then succumb to infections and fall sick. In severe or prolonged cases, this may lead to death. Stress can be acute or chronic. Chronic cases are less obvious to the eye but result in reduced feeding response, higher FCRs and lower returns.

Fish are cold-blooded animals and respond directly to environmental conditions. Aquaculture systems are innately unstable. This is because, their environmental components (chemical, physical and biological) are constantly changing, as fish biomass and nutrient inputs (feed) increase over time. The challenge to the farmer is to maintain environmental parameters within the fishes normal to tolerance limits during the course of production. For eg. Catfish do not have scales to protect them so rely on mucous to protect their skin. When the mucous is rubbed off, the catfish are very prone to infection and parasites. In addition Fish do not have eyelids and cannot protect their eyes when they are being rubbed against each other or being poured from a basket or net.

The preventive measures of poor and reduced growth include:

• Good water quality management. This begins by picking a farm site with good water quality and quantity. Maintain water quality at non-stressing levels.
• Good nutrition. Feed quality feed with a proper nutritional ration.
• Good stocks of fish. Only stock healthy, unstressed and disease free fish and handle them properly.