Fish predators and their management

Usually before fish are harvested, in the course of production, they come across predators that can cause minimal and severe damage to the fish in the pond, leading to losses for the farmers. Managing them is therefore important.

• Birds such as grey heron are some of the fish predators during the day and can be controlled by scaring them.
• Otters are other fish predators. These however feed at night and are difficult to control though traps are sometimes effective.
• Humans are also considered fish predators. They can come either during the day or night and catch the fish. However, setting up your fish pond close to your home gives you opportunity to control this.
• Predators such as birds and otters should be taken seriously because they can cause up to 75% losses. Humans through theft, though the chances might be low, can cause nearly 100% losses

Fish disease, parasites and their control

Fish have generally a number of parasites and diseases. However this manual will concentrate on the most common ones in Malawi.

Gas bubble disease

This disease comes due to excessive aeration in intensive culturing facility and, may best apply to the large scale fish farming. Small scale fish farmers can also experience this disease though chances may be low.

• It is common where artificial aerators are used
• Water in the culturing facility become supersaturated with dissolved gases
• This can cause high mortality for both fish fries (baby fish) and the older ones
• It is advisable to avoid supersaturating rearing facilities with gasses by relying on natural air particularly in extensive fish culture.
• Farmers using artificial aerators can use saturometer to determine excess gas pressure.
• Farmers can reduce gas pressure in the culturing facility through splashing the water and using water with lower gas pressure.

Trichodina parasite

• Trichodina is a saucer-shaped parasite that attacks fish skin and gills.
• It is common among cultured tilapia, especially when the fish are farmed at high stocking densities.
• The prevalence of infection is high in larger fish than in smaller fish.
• Parasitism increases with decreasing water temperature

Typical signs of the disease

• Skin and gill damage
• Respiratory distress
• Loss of appetite and loss of scales.

Prevention  

• Reduce fish stocking density