Finfish Breeding and Hatchery Management

Unit 3 - Breeding of major carps

3.9.2. Bacterial and fungal diseases in carp rearing systems

• Bacteria can cause diseases either as secondary invaders or as primary pathogens.
• Bacterial diseases in larvae can be broadly classsified as surface ulcerative, acute systemic and chronic granulomatous type.
• Surface ulcerative type of diseases are characterized by haemorrhagic surface ulcers and are normally caused by Aeromonas, Pseudomanas, Vibrios, Flexibacteria, Myxobacteria, etc. Surface ulcerative disease conditions at times develop to acute systemic disease.
• These are characterized by the presence and proliferation of bacteria in internal organs like kidney, heart, spleen, blood and other visceral organs.
• These diseases produce significant necrotic changes in all the affected organs and can cause mortality in a short time scale.
• Bacterial haemorrhagic septicaemia caused by numerous serotypes of Aeromonas hydrophila is a major problem.

Treatment chart for common disease conditions of carp larval rearing systems

Disease agent	Chemical	Method	Concentration/time
1. Ectoparasitic protozoans
a. Ichthyophthirius sp.	Formalin	Short bath	60-100 ppm for 30 minutes
b. Trichodina sp.	Formalin	Long bath	20-30 ppm
c. Epistylis & Vorticella	Formalin	Dip	200-300 ppm for 1 minute
d. Ichthyobodos sp.	Formalin	Dip	20-30 pm for 30 minutes
2. Monogenetic worms
a. Dactylogyrus	Organophoshporus pesticides	Dip	10 ppm for < 1 minute
b. Gyrodactylus	Nuvan, Dipterex	Long bath	0.5 ppm for 24 hours
3. Crustaceans
a. Lernaea	Nuvan, Dipterex	Long bath	0.5 ppm for 24 hours
b. Argulus	Nuvan, Dipterex	Long bath	0.5 ppm for 24 hours
4. Endoparasites
a. Sporozoans	Nuvan, Dipterex	Long bath	0.5 ppm for 24 hours
b. Cercaria and metacercaria of digenetic trematodes	Nuvan, Dipterex	Long bath	0.5 ppm for 24 hours
5. External Mycosis – Saprolegnia	Malachite green Formalin	Dip Bath Bath Dip	60 ppm for < 1 minute 1-2 ppm for 1 hr 50-75 ppm for 30 minutes 100-200 ppm for 1-3 minutes
6. Surface bacterial diseases	Proflavine Oxytetracycline & Furnace	Bath Short bath	20 ppm 1-5 ppm
7. Systemic bacterial diseases	Furazolidone Oxonilic acid Chloramphenicol	In feed In feed In feed	50mg /kg fish/day 10mg/kg fish/day 50 mg/kg fish/day

Gas disease

Heavy mortality of fish seed due to `gas disease’ has been observed on several occasions. The symptoms of the disease are the presence of gas bubbles in gill filaments, heart and blood vessels and also in the gut. The air bladder gets highly distended. The `gas disease’ also referred to as ‘gas embolism’ occurs due to supersaturation of water with either oxygen or nitrogen and is generally encountered in fish nurseries.