Finfish Breeding and Hatchery Management (2+1)

3.9.1. Common disease problems in carp hatcheries and early rearing systems

Unit 3 - Breeding of major carps

3.9.1. Diseases and parasites in carp hatcheries

The nursery and rearing systems of carps are often very rich organically and provide an ideal environment for many of the pathogens. Important problems in hatcheries and early rearing systems are caused by some of the following pathogens:

1. Protozoan ciliates like Ichthyophthirius multifilis (white spot disease), Trichodina complex and ectodermal ciliates like Epistylis, Vorticella. All these ectoparasites can cause mass mortality of younger stages of carp very quickly and the situation becomes worst in waters with low oxygen and high organic matter.

2. Disease caused by Myxosporidians are a serious threat to the fish seed farms. These sporozoan spores present in the pond soil are normally ingested by the developing fry. Once inside the target tissue the sporozoans cause massive destruction of their target tissue and produce large scale mortality.

3. Worm parasites like Dactylogyrus (gill fluke) and Gyrodactylus (skin fluke) with their well developed attachment haptor and feeding apparatus can cause mortality in early developmental stages of carps.

4. Opportunistic secondary bacteria (Aeromonas) and fungi (Saprolegnia) can become serious problem in fish larvae which are heavily parasitized.

In carp rearing ponds major problems are because of larger ectoparasites, secondary invaders, systemic bacterial pathogens and viruses. Ectoparasites like Dactylogyrus and Argulus (fish lice) and endoparasites like sporozoans are very important. Bacterial problems like surface ulcerative conditions and acute systemic diseases are common in carp rearing systems. Many a times mortalities seen in carp culture systems are a result of ectoparasitic and systemic bacterial diseases. External fungal problems are normally associated with fish which are poorly handled. The possibility of viral diseases causing mortalities in carp nurseries cannot be ruled out.