Intensity of parasitic infestation in silver carp, Hypophthalmichthys molitrix

Intensity of parasitic infestation in silver carp, Hypophthalmichthys molitrix 1 first-author 1 1 2 2 2 corresp ‡Corresponding Author ‡Corresponding Author †E-mail:skdas_maa@yahoo.comsimon@ukm.my †E-mail:skdas_maa@yahoo.comsimon@ukm.my skdas_maa@yahoo.com Department of Fisheries, University of Rajshahi, Rajshahi 6205, Bangladesh Department of Fisheries, University of Rajshahi, Rajshahi 6205, Bangladesh School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, D.E., Malaysia School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, D.E., Malaysia Silver carp, Hypopthalmichthys molitrix is one of the most economically valuable fish species in Bangladesh. However, its production is often hindered by parasite-induced mortality. The present study reports the intensity of parasitic infestation in 216 specimens of H . molitrix collected from different fish markets in Rajshahi City, Bangladesh. Nine different parasite species ( Trichodina pediculatus , Dactylogyrus vastator , Ichthyophthirius multifilis , Gyrodactylus elegans , Lernaea sp., Apiosoma sp., Myxobolus rohitae , Camallanus ophiocephali , and Pallisentis ophiocephali ) were recovered from the gill, skin, stomach, and intestine of host fish. The highest level of infection was observed for host skin, while lower levels were observed for host gill, stomach, and intestine. The results also revealed that the intensity of parasite infection in different organs of H . molitrix varied with the season. In particular, the highest levels of infection were recorded during the winter period (November–February), when fish are most susceptible to parasites. The findings of the study will help in the management and conservation of H . molitrix . Freshwater fish Disease Parasites Carp fishery Infestation Aquaculture Bangladesh Introduction 1 Diseases of freshwater fishes in Bangladesh are a severe threat to aquaculture. Many of them (15%–20%) are associated with parasite infestation (Chowdhury, 1998 1998 ). Parasites interfere with host nutrition, metabolism, and secretory functions of the alimentary canal, and can even damage the host nervous system (Markov, 1961 1961 ). Intense parasite infection can also cause ulceration, and upset the normal course of reproduction (Rahman and Jahan, 2002 2002 ; 2005 2005 ). All these effects may induce host mortality. Piscivorous animals may become infected consequent to the consumption of parasitized fish (Faust, 1939 1939 ). The intensity of fish parasitic infection is greatly influenced by seasonality, which affects host ecology and physiology (Pennycuick, 1971 1971 ; Rahman et al., 2007 2007 ). Bashirullah ( 1973 1973 ), Ahmed and Sanaullah ( 1977 1977 ), Ahmed ( 1981 1981 ), Zaman et al. ( 1986 1986 ), Hossain et al. ( 1994a 1994a ; 1994b 1994b ), Hafizuddin and Shahabuddin ( 1996 1996 ), Akther et al. ( 1997 1997 ), Rahman et al. ( 1998 1998 ), Parween and Rahman ( 2000 2000 ), Banu and Khan ( 2004 2004 ), Ahmed et al. ( 2009 2009 ), and recently Mofasshalin et al. ( 2012 2012 ) provide some preliminary information about the parasitofauna of freshwater fishes in Bangladesh. Marine fisheries dominate total fish production in Bangladesh; nevertheless, freshwater aquaculture has grown rapidly, and contributes an increasing share of fish available for consumption. Fish from aquaculture trebled in the period from 1989 to 1999. About 85% of fish produced in ponds are carp (DOF, 2011 2011 ), and include exotic carp species such as silver carp ( Hypopthalmichthys molitrix ) (Valenciennes, 1844) and common carp ( Cyprinus carpio ) (Linnaeus, 1758), and indigenous carp species. Among the farmed carp species, silver carp is very popular in Bangladesh especially in northwest areas of the country. Although several studies have been conducted on freshwater carp in Bangladesh, none of them focused on the intensity of parasitic infestation in silver carp in Bangladesh. In the present study we determine the intensity of infestation and organ-wide distribution of parasites of H . molitrix . Materials and methods 1 Specimens of silver carp were collected every week at regular intervals from different fish markets in Rajshahi City, Bangladesh (Fig. 1 1 ) over a period of six months from September 2009 to February 2010. All the silver carp available from those markets were landed from the adjacent ponds, beels, and other water bodies. The specimens were kept in a refrigerator soon after collection and examined generally within three to five days. The black box denotes the study area The host specimens were first examined using a magnifying glass to find ectoparasites on the skin and gills (Mofasshalin et al., 2012 2012 ). To collect the endoparasites, individual fish were dissected by an incision through the mid ventral longitudinal line. The viscera were removed and put into physiological saline solution (0.7% (7 g/L) NaCl). Then the stomach, intestine, and liver were examined separately for endoparasites. The stomach and intestine were split open and were shaken in a tube to dislodge any parasites attached to the epithelial lining. Sometimes the epithelial layers of the stomach and intestine were scraped with a scalpel to remove the parasites. The parasites found were carefully removed and preserved in individual vials in 70% alcohol with few drops of glycerine for 24 h. Protozoan parasites were examined at high magnification under a binocular microscope and the other parasites were washed with fresh saline solution, then fixed in alcohol-formalin-acetic acid (AFA) solution and heated with a spirit lamp to 70–75 °C. The parasites were again washed with 70% alcohol, temporarily mounted in Canada balsam on slides, and finally examined under a compound microscope (BX51, Olympus, Japan) and identified according to Chandra ( 2004 2004 ). The prevalence, abundance, and mean density of parasites were estimated according to Margolis et al. ( 1982 1982 ). Results and discussion 1 Throughout the study period, a total of 216 specimens of silver carp were examined, leading to the identification of nine different parasite species (seven ectoparasites and two endoparasites). The ectoparasites were found mainly in the skin (the whole body surface of the hosts as well as the fins) and gills of the host fish. Three species of ectoparasites, Trichodina pediculatus (Muller, 1786), Dactylogyrus vastator (Nybelim, 1924), and Ichthyophthirius multifilis (Fouquet, 1876) were collected from the gills (Table 1 1 ). The other four ectoparasites, collected from the skin, were Gyrodactylus elegans (von Nordmann, 1832), Lernaea sp. (Linnaeus, 1785), Apiosoma sp. (Blanchard, 1885), and Myxobolus rohitae (Butschli, 1882). The ectoparasites Lernaea and Apiosoma were identified only to genus level because of their complex taxonomic features. The endoparasites Camallanus ophiocephali (Pearse, 1955) and Pallisentis ophiocephali (Datta, 1936) were found in the stomach and intestine respectively of the hosts during the study period (Table 1 1 ). Farhaduzzaman et al. ( 2010 2010 ) reported most of these parasites in Labeo rohita (Hamilton, 1822) from Rajshahi, Bangladesh, Mofasshalin et al. ( 2012 2012 ) also reported similar parasites in three Indian minor carp ( L . bata , L . gonius , and C . reba ) from the freshwater bodies of Rajshahi, Bangladesh. Type of parasites Name of parasites Infected organ Ectoparasites Trichodina pediculatus Gill Dactylogyrus vastator Gill Ichthyophthirius multifilis Gill Gyrodactylus elegans Skin Lernaea sp. Skin Apiosoma sp. Skin Myxobolus rohitae Skin Endoparasites Camallanus ophiocephali Stomach Pallisentis ophiocephali Intestine Organ-wise fluctuation in the prevalence, abundance and mean density of total parasites is reported in Fig. 2 2 . Skin parasites had the highest prevalence (51.38%), while stomach parasites had the lowest (10.77%). Gill parasites had high prevalence too (43.05%). The highest parasite abundance was found in the skin (with an average of 1.25), while the lowest was found in the intestine (0.30). By contrast, the mean density value was highest in the stomach (4.00), and lowest in the gills (2.06) and in the skin (2.43). These observations on parasitic infestation are consistent with those of Farhaduzzaman et al., 2010 2010 and Mofasshalin et al. ( 2012 2012 ) in carp fishes of Bangladesh. Rahman and Parween ( 2001 2001 ), Alam et al. ( 2006 2006 ), and Rahman et al. ( 2007 2007 ) observed similar parasitic infestation in different freshwater fish species of Bangladesh. Monthly fluctuations in the overall prevalence, abundance, and mean density of total parasites are shown in the Fig. 3 3 . The highest parasite prevalence (75.0%) was observed in December, while the lowest (41.6%) was observed in October. Secondary peaks of prevalence (66.6%) were observed in November and January. The overall highest mean abundance value was 3.83 (recorded in December), while the lowest was 1.25 (recorded in September). A second peak of 3.08 was recorded in January. The highest mean parasite density (5.11) was observed in December, while the lowest (2.50) was observed in September. The intensity of parasites in different organs of H . molitrix varied with the season, being higher during winter (November–February). Winter had already been identified as a period of high susceptibility of fish to parasites (Rahman et al., 2007 2007 ; Farhaduzzaman et al., 2010 2010 ; Mofasshalin et al., 2012 2012 ). Conclusions 1 The present study describes the intensity of parasitic infestation in different organs of silver carp H . molitrix . During the study period we identified nine parasite species. The highest peak of parasite abundance and prevalence was recorded in December, while the lowest was recorded in September. This might be due to their feeding preference, stocking density, water depth, and temperature along with other physico-chemical parameters and management practices. 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Our heartiest thanks go to the ichtyology laboratory technicians, University of Rajshahi, Bangladesh for their support throughout the study. 10.1631/jzus.B1200121 Project supported by the Universiti Kebangsaan Malaysia (UKM) through Young Researcher Incentive Grant (No. GGPM-2011-057), and UKM Research Grant (No. UKM-OUP-FST-2012) 2012-04-23 2012-11-12 2012-09-06 2022-01-05 Copyright © Zhejiang University and Springer-Verlag Berlin Heidelberg 2012 2012 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 12 13