Crustacean Diseases in Fishes
a. Argulosis Disease:
- Argulus or Fish Lice is a common copepode parasite in fishes.
- It is a large ectoparasite and can move over the body surface of the fish.
- Argulus puncture the skin and inject cytolytic toxin through the oral sting to feed on the blood.
- The feeding site becomes a wound and haemorrhagic, providing ready access to secondary infection of other parasites, bacteria, virus and fungi.
- Argulus transmits dropsy in fishes. In advanced stages, fish swim erratically, show growth loss and loss of equilibrium.
- To control Argulus, remove the submerged vegetation, wooden lattices placed in the pond will serve as artificial substrate to deposit its eggs, which can be removed at intervals to kill the eggs.
- 500 ppm of ammonium chloride, 410 ppm of balsam, 10 ppm of DDT for 25 seconds dip, 0.25 ppm of dylox and 2000 ppm of Lysol for 15 second dip are effective to kill Argulus.
b. Lernaeasis Disease:
- It is caused by a copepode parasite, Lernaea or Anchor Worm.
- This disease is mostly caused by L. cyprinacea.
- The larval stages are temporary parasites that feed on mucous and blood of fish.
- The adult female is a specialized fish parasite, worm like, which burrows into the fish flesh, keeping its eggs cases protruding out of the fish body.
- Male Lernaea do not attack the fish and are not specialized for parasitic life.
- Early infected fish swim erratically, flashing against the sides and bottom of ponds. Heavily infected fish swim upside down or hang vertically in the water.
- Only partial control of Lernaea is possible with chemicals. Because, the head is buried in the fish tissues and there are no exposed respiratory organs.
- Hence, prevention is more effective than control. 1% common salt eliminates larvae in 3 days, 250 ppm formalin for 30 to 60 minutes.
- 0.2 ppm gammexane for 72 hours, 2 ppm of lexone, 0.1 ppm lindane for 72 hours and 1 ppm chlorine for 3 days may give good results
c. Ergasillus and salmincola Diseases:
- These two parasites are responsible for huge mortality of fishes in the culture systems.
- These two parasites are found attached to the gill filaments and feed on blood and epithelium. Later they may also be found on the fins and body.
- The infection results in impaired respiration, epithelial hypertrophy, anaemia, retarded growth, restlessness and finally death.
- The fish becomes susceptible to secondary infection, especially fungus.
- Ergasilus can be treated successfully with a combination of 0.5 ppm copper sulphate and 0.2 ppm ferric sulphate for 6 to 9 days.
- Salmincola can be controlled with 0.85% calcium chloride, 0.2% copper sulphate, 1.7% magnesium sulphate, 0.2% potassium chloride and 1.2% sodium chloride for 3-4 days.
- Achtherespercarum is a common parasite attached to the gill rakers of fishes. But, does not damage gill filaments. It can also be controlled by the above chemicals.