ABSTRACT
Biological diversity (or biodiversity), defined as the number and variety of living organisms within a specific geographical region, is essential for the stability of ecosystems, protection of overall environmental quality and understanding the intrinsic value of all species on earth (Ehrlich and Wilson 1991). Parasites, constituting more than half of all biodiversity (Toft 1986), are the integrative core of biodiversity survey and inventory, conservation and environmental integrity and ecosystem function (United States Department of Agriculture 2009). This article highlights the need for studies researching biodiversity of fish helminths, the largest and the most important group of fish parasites, with special reference to monogenoids occurring in Arunachal Pradesh waters. The state of Arunachal Pradesh (29°30' N; 97°30' E) is recognized as the 25th biodiversity hotspot in the world (Chowdhery 1999), among the 200 globally important ecoregions (Olson and Dinerstein 1998) and is also one of the hotspots of freshwater fish biodiversity in the world (Kottelat and Whitten 1996). The state has no less than 213 recorded fish species (Bagra et al. 2009) having elements of Indo-Gangetic, Myanmarese and south Chinese regions (Yadava and Chandra 1994). Not only do these fish provide nutritious food, but they also part of an unbreakable relationship with the culture, religion and traditions of the region (Vishwanath 2002). Recognizing the future potential of fishery culture, the state government initiated the ‘state fisheries programme’ from as early as 1958, which is now regarded as one of the most important sectors involved in the socioeconomic upliftment of the tribal population of the state (Government of Arunachal Pradesh 2011a). Disease, and much of it due to parasites, is the single most important factor threatening the fishery industry worldwide, particularly in the tropics (Schmidt and Roberts 2000). Among the parasites that infect freshwater fishes, helminths – represented by 5 well characterised taxonomic units, Monogenoidea,1 Trematoda (comprising Digenea and Aspidogastrea), Cestoda, Nematoda and Acanthocephala – form a major group and often cause veterinary problems worldwide (Williams and Jones 1994). Helminth parasites are important not only because they cause fish diseases but also because they are an essential component of global biodiversity (Poulin and Morand 2004). As much as 30000 helminth species have been estimated to be parasites of fish (Williams and Jones 1994). Monogenoidean parasites are the most ubiquitous and abundant parasites in the aquatic environment (Ivona 2004). These are mainly ectoparasitic on gills and/or external surfaces of freshwater and marine fishes (Bychowsky 1957); a few species become endoparasitic by inhabiting the palleal cavity of cephalopods and urinary bladder and rectum of amphibians and reptiles (see Euzet and Combes 1998 and the references therein). These worms feed on blood (Hayward et al. 2007) and/or epithelial cells and mucus of fish (Buchmann and Bresciani 2006), causing direct loss due to mortality, usually to younger fish and those in intensive culture/captive conditions (Thoney and Hargis 1991). Damage is frequently indirect when these worms degrade the mucous layer, making the host fish susceptible to secondary pathogens such as bacteria and fungi (Grimes et al. 1985). The economic effects of infestation include a decrease in and/or rejection of otherwise edible fish products leading to subsequent loss of interest in the aquaculture industries (Jones 2001). Chemicals and freshwater/marine baths are often used to control monogenoids but these methods can be very expensive (Whittington et al. 2001).