Endoparasite of fish

cestodes- diphyllobothrium and ligula spp.

1. Endoparasite of fish:Cestode

2. Introduction Cestodes are endoparasitic tapeworms. They are parasitic in the intestine of the host Larval cestodes are commonly found in fish, often encysted amongst the viscera and musculature. CAUSATIVE AGENT: Asian tapeworm- Bothriocephalus acheilognathi Ligula intestinalis

3. Aetiology Body is ribbon-like, segmented or unsegmented , 5-70 mm long The cestodes are also endoparasitic with at least one intermediate host in their life cycle. Usually the body ( strobila ) is subdivided into a number of segments ( proglottids ) each containing a single set of reproductive organs

4. A scolex (attachment organ) is present at the anterior end. The adult worms are usually white in colour and may be very elongated The scolex of these larvae is fully developed, but the strobila is usually relatively short and unsegmented. . All cestodes are oviparous and the eggs passed in the faeces of the final host may or may not hatch in water to release a free-swimming larva coracidium .

5. Life cycle The cestodes of fish have a life cycle involving at least one other host. Fish may serve as final or inter- mediate hosts for cestodes . Whether ingested as larvae coracidium or egg the larval cestode penetrates through the gut wall of the host and undergoes further development in the body cavity to a stage capable of infecting the fish host. In most orders of cestodes , this stage is known as a procercoid . If the procercoid is ingested by a suitable fish host, it penetrates through the gut wall and encysts in the viscera or musculature where it develops to the plerocercoid stage. . The life cycle of this group of cestodes is completed if an infected fish is eaten by a suitable final host. This may be another fish , a bird or a mammal, in the gut of which the cestode develops to maturity

6. Life cycle of cestodes

7. Host range Minnows Golden shiner Various carp species ( cyprinidae ) Poecilidae . Centrachidae Channel catfish Aquarium fish, such as discus and other cichlids

8. transmission Many piscivorous birds or mammals can act as a final host for cestodes Development ceases at 12 ° C. Worms mature in about 21 days at 28 ° C in 2 months at 15 ° C. The plerocercoids are transmitted by copepods. Several copepod genera can be intermediate hosts and the distribution of infections depends largely on the abundance of the intermediate host

9. External pathology Affected fish are sluggish. Emaciated body because of non-feeding Gut blockage Abdomen Chronic mortality.

10. Internal pathology This parasite is commonly found in intestine of fish . Migrating plerocercoids may cause adhesions and severely damage viscera or muscle because of pressure necrosis. Ligula causes peritoneal adhesions and pressure atrophy of the liver, gonads , and body wall musculature of cyprinids worldwide. Ligula intestinalis in a cyprinid. The body wall has been cut, revealing the peritoneal cavity filled with a single plerocercoid ( P ). Part of the worm remains in the peritoneal cavity.

11. DIAGNOSIS: Gross examination of the intestine of host fish . Worms are easily identified as cestodes from wet mounts or histopathology. F rom wet mounts of fecal contents having proglottids or eggs can be detected. Histological section through a cestode ( C ), Bothriocephalus acheilognathi , filling the lumen of the intestine ( I ) of a minnow. Giemsa stain .

12. pathogenesis The parasite may induce hemorrhagic enteritis due to destruction of the intestinal epithelium & eggs are found in intestine and peritoneal cavity grossly. Adult stage of the parasite interferes with absorptive processes of the intestine and may reduce food intake . Secondary microbial infection is possible. Some fish cestodes are important human parasites.

13. PREVENTION AND CONTROL • Elimination of intermediate hosts (copepod) Disinfection of culture facilities with quick lime to destroy cestode eggs Praziquantel 300 mg/kg feed orally for every 4 th day for 1month is effective in treating adult cestode infections. Aquarium fish should not be fed live foods that might transmit larval cestodes . In farms using surface water, filtering the water to exclude the intermediate host can prevent infections

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