Fish Diseases and Parasites

triadInfections in aquaculture are spread across a fish's life cycle (egg to adult stage). The most important cause of mortalities of eggs and larvae are fungal, parasitic and bacterial infections. However mature fish are not as susceptible as fry and fingerlings. Infections most frequently encountered in aquaculture set-ups are fungal, parasitic, viral and bacterial.

Fungal diseases

The most common fungal infection is caused by saprolegnia. The infected eggs/larvae are covered with a cotton-like growth. During the incubation of the eggs and larvae it is recommended to treat them with Malachite green 0.1–0.2 ppm once a day. A stock solution of 10 gram of malachite green in 1 litre of water is recommended.

Parasitic diseases
The most commonly found ecto-parasites are: Dactylogyrus, Trichodinia, Costia, Chilodonella and Gyrodactylus. Fry and fingerlings can be treated with 20–25 ppm formalin.

Bacterial diseases
Two most common bacterial infection are caused by a myxo-bacteri (Flexibacter) and by an Aeromonas (oedemic disease). Both infections can be treated with antibiotics as; oxytetracycline (bath, 50 ppm for 5 days), Furataldone 10 ppm in combination with penicillin 10 ppm (bath, 4–5 days).

Control of Parasites and Diseases

Fouling of water, crowding, and fish stress can render fish vulnerable to parasites and fungal infection. Parasites may inhabit the external (skin, fins, gills) and internal (body cavity, eyes, organs, flesh) parts of the fish (Tilapia hatchery and Nursery Management, 1997).