World Aquaculture - September 2023

WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2023 65 aquaculture. African catfish and its hybrid entered clandestinely into Indian culture systems via Bangladesh through private fish traders and rapidly spread into whole of the country (Bhakta and Bandyopadhyay 2007, Singh and Lakra 2011, Singh et al. 2015). Gophen (2015) presented a pathetic account of the ecological devastation of fish communities of Lake Victoria’s unique ecosystem, including damage to about 400 endemic species of Haplochromine fishes, by the introduction of Nile Perch (Lates niloticus). The introduction resulted in Nile perch becoming the dominant fish species (Kumar 2000, Ploeg 2008, Gophen 2015). Lion fish (Pterois volitans) were introduced into Florida coastal waters as a result of escapes after hurricane Andrew in 1992 and possibly also deliberate releases as tourist attractions for divers at wrecks along the coast (Ploeg 2008). A study of parasites of Hawaiian fishes indicated native fish from streams where no exotic fishes were found were completely free of adult helminthic parasites and implicated the exotic poecilid gambusia affinis, introduced for control of mosquitoes, for introduction of parasites in areas where the fish was used (Blazer and Lapatra 2002). Pathogens are important factors in the health of both cultured and cultured wild fish populations (Blazer and Lapatra 2002). The use of antibiotics in acclimatization of exotic fish species to control or treat disease may also present some risks. Antibiotics entering the ecosystem from waste waters could act as immunosuppressants or foster development of antibiotic resistant strains of pathogens (Schmidth et al. 2000, Blazer and Lapatra 2002). Scholz and Salgado-Maldonado (2000) suggest the digenetic trematode Centrocestus formosanus, which infects numerous fish in the US, entered through the importation of infected snail hosts from Asia in 1979. A study of infectious hematotropoietic necrosis virus (IHNV) genetic heterogeneity and viral traffic by Anderson et al. (2000) suggested that both virus evolution and introduction of new IHNV strains contributed to genetic diversity. Exotic aquatic species may not only import diseases that affect related species, but humans as well. Escaped or introduced fish may serve as hosts or vectors for pathogens in new environments. Mycobacteriosis of fish is a common chronic progressive disease all over the world which affects wild and cultured marine, brackish and freshwater fish (Acha and Szyfres 2003). Mycobacteriosis of aquarium fish in the Czech Republic is one of the most commonly diagnosed bacterial diseases (Novotny et al. 2004a, Novotny et al. 2004b). Exotic fish may also affect local ecological systems by preying on wild organisms and creating imbalances in the food chain. The piranhas, predatory fishes from South America, poses great risk to tropical habitats where they are permitted in the aquarium hobby. Considering the threats posed by the African catfish and piranhas, the Indian ministry of Agriculture ordered the killing of these fishes en masse (Kumar 2000). Increased abundance of fish following mass escapes may also attract predators, thereby increasing the overall predation pressure throughout the immediate vicinity (Myrick 2002). Although cultured fish and farm bred ornamental fish often exhibit poor adaptation to natural environments, the establishment and dominance of Heterotis niloticus in the Cross River basin following escape from a fish farm supports Myrick’s (2002) suggestion that escaped organisms that are native to nearby regions have a higher probability of short term survival than exotic organisms from different eco-regions. Other Introduction Pathways Anglers may introduce fish for diverse fishing experiences. Chub (Leuciscus cephalus) were illegally introduced to the Inny River, by Irish anglers in the early 2000s. Inland Fisheries Ireland commenced an eradication programme in 2006, employing electric fishing to physically remove chub from the river (FAO 2016). Although the eradication of established invasive species is often impossible (Pimentel et al. 2005); Ireland successfully removed all chub from the infested river. Ballast water is a less mentioned source of introductions. Ballast tanks are filled and emptied at different locations, mostly in marine and brackish habitats, and species picked up during a filling that are able to survive when emptied back into new environments can become established. Eurasian zebra mussels, Dreissena polymorpha and the American comb jelly, Mnemiopsus leidyi are examples of ballast water introductions (Bhaskar and Pederson 2000). The mussels reproduce rapidly, clogging pipes in municipal water supplies and industries, and clean-up or control efforts are an expensive venture. Management Strategies to Reduce Risks Myrick 2002 suggested several management options including inventory control, recapture contingency plans, monitoring/ notifications and species selection. Education and enlightenment will play a big role in control of both intentional and accidental introduction of species into new environments. Liu et al. (2013) are Established populations of ornamental species such as mollies, guppies, platys and swordtails are well-known around tropical and subtropical ornamental fish production areas. Photo by C. Greg Lutz (CONTINUED ON PAGE 66)