JaiGopal Sharma

Biological Mosquito Control is affected by Alternative Prey

BackgroundMosquitofish were introduced to several countries of the tropics and subtropics as biological agents for the control of mosquito larvae. Meanwhile, they became a threat to native communities and fish worldwide, similar to other invasive species through resource competition, overexploitation, or habitat alteration. We investigated prey selectivity patterns of Gambusia affinis (mosquitofish) preying on larvae of the two Indian major carps (Catla catla and Labeo rohita) in the presence of varied proportions of alternative prey (rotifers, cladocerans, chironomid and mosquito larvae) under laboratory conditions.ResultsThe patterns of prey selectivity in mosquitofish were influenced by the presence of alternative prey and their relative abundance in the environment. Carp larvae, when present in equal proportions, were randomly selected by mosquitofish, however, positively selected when present in higher proportions. In the presence of Hexarthra mira, Daphnia similoides or the mosquito larval instar-IV as an alternative prey, the mosquitofish preferred fish larvae regardless of prey proportions. In the medium where either mosquito larval instar-I or chironomid larvae were given as alternative prey, the mosquitofish either rejected or randomly selected the carp larvae. Given a multispecies prey combination, mosquitofish primarily selected the larvae of L. rohita and mosquito larval instar-I. We also found a prey switching ability of mosquitofish in relation to varying abundances of prey species in the environment.ConclusionsThe present results suggest that mosquito immatures are not the preferred food of mosquitofish when fish larvae are present in their natural habitats. Since mosquitofish and carp larvae have overlapping natural habitats and prey preferences are the invasive mosquitofish may have a substantial impact on native communities of invertebrates and fish. This way, they are equally important for extensive fisheries and conservation management.

Effect of UV-B Radiation on the Defence System of Labeo Rohita (Actinopterygii: Cypriniformes: Cyprinidae) Larvae and its Modulation by Seed of Devil's Horsewhip, Achyranthes Aspera

Solar ultraviolet B (UV-B, 280–320 nm) is a potent environmental stressor to aquatic organisms. UV-B radiation affects both wild and cultured species. The effect of UV-B on aquatic organisms depends on the capacity of the radiation to penetrate into the aquatic environment, which is determined by the depth of the water column, presence of dissolved organic carbon, and the quantity of organic and inorganic particulate matter (Hader et al. 1998, 2007, Bancroft et al. 2007). The harmful effects of UV-B include damage that compromises the physiology, biochemistry, reproduction, and growth of the exposed animals (Lesser et al. 2001, Armstrong et al. 2002, Van Uitregt et al. 2007, Nahon et al. 2009). In fishes, UV-B radiation can induce injury to the skin, including sunburn and appearance of sunburn cells, epidermal hyperplasia, depletion of the mucus layer, or even sloughing of the epidermis solar elastosis with wrinkling, melanomata (Bullock 1988, Berghahn et al. 1993, Little and Fabacher 1994, Blazer et al. 1997, de Oliveira Miguel et al. 2003, Sharma et al. 2005). These changes in the skin can be accompanied by infections. The skin lesions of Atlantic salmon, Salmo salar L., contained Vibrio spp., and mycobacteria (McArdle and Bullock 1987). UV-B irradiated rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), had skin fungal pathogens (Saprolegnia) (see Fabacher et al. 1994). Thus the primary barrier of the defence system becomes damaged and the normal physiology of fish is affected due to the radiation. The immune system of fish can be strongly modulated by UV-B radiation (Salo et al. 2000). UV-B exposure induces pronounced immunomodulation in cyprinids (Markkula et al. 2006). The digestive physiology and immune system of catla, Catla catla (Hamilton, 1822), were affected by UV-B radiation (Sharma et al. 2010). Outbreak of diseases seriously affects the freshwater aquaculture industry, especially in the developing countries. The majority of the freshwater species are vulneraACTA ICHTHYOLOGICA ET PISCATORIA (2013) 43 (2): 119–126 DOI: 10.3750/AIP2013.43.2.04