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Seasonal analysis of food items and feeding habits of endangered riverine catfish Rita rita (Hamilton, 1822)

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Abstract

This investigation presents the food and feeding activity of and endangered riverine catfish Rita rita, during February 2017-January 2018. A total of 225 fish individuals was analyzed for stomach contents by characterizing the dominant food items and morphometric features. The results divulged ten major food items consumed, preferably fish scales and eggs, teleost fishes, copepods, cladocerans, rotifers, and mollusks. Total length and body weight of fish varied between 9-34 cm (20.53 ± 6.90 cm) and 10-400 g (9125.94 ± 102.07 g), respectively. The index of relative importance (IRI%) showed the importance of rotifers over the other food items. Morisita's index of diet overlap indicated seasonal variations in catfish diets with summer and monsoon displaying the least overlap, while maximum overlap during monsoon and winter seasons. The non-metric multidimensional scaling (nMDS) indicated the close association between the food items available during summer and winter seasons with a significant difference among the seasons (ANOSIM, R = 0.638, P = 0.013). Levin's niche breadth index arranged in the order of 0.88>0.81>0.78>0.63>0.43 for the size classes of V, IV, III, II and I, respectively. The PCA explained 95.39% of the total variance among the food items and fish size groups. Small-sized fish individuals displayed a greater correlation with food items suitable for their mouth size. In conclusion, the variety and frequency of food items recorded indicated considerable feeding plasticity and opportunistic feeding behavior with a shift from carnivorous to omnivorous feeding nature. This study could render useful information on the food and feeding habits of R. rita and provide background for preparing its diet for future aquaculture practices.

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Arsenic (As), mercury (Hg) and cadmium (Cd) are one of the greatest threats to aquatic biota for their persistence, bioaccumulation and biomagnification across the globe. This study presents the first hand data of toxic trace metals in edible fish muscles, sediments and water sampled from Head Punjnad (HP), Pakistan during 2017. The likely reason for the selection of HP as a study target was its emergent prominence as an irrigation hub and holidaymakers spot largely for angling and feasting. The investigated five fish species are Ctenopharyngodon idella, Oreochromis niloticus, Eutropiichthys vacha, Rita rita and Sperata sarwari. The results divulged the pattern of metals concentration in fish in the order of Cd > As > Hg. However, R. rita, O. niloticus and C. idella showed higher accumulation of the metals that clearly alluded to species-linked metal bioaccumulation, which might be due to their unique feeding mood. Cadmium presence ranged between 0.04-1.12 ppm while As and Hg fluctuated between 0.01-0.04 and 0.001-0.18 ppm, respectively. Conversely, higher bioaccumulation was detected in gills rather than the muscle tissues that evidently indicated gradual water quality degradation conceiving higher metal concentrations in the environment. Similarly, a higher concentration of Cd was observed in water (0.78 ppm) and sediment (0.64 ppm) samples. In acquiescence to the above-given outcomes, the metal concentration hierarchical arrangement in sediment and water was identical to the witnessed in fish species (Cd > As > Hg). In conclusion, this study established that selected metals level in HP water and sediments displayed levels higher than the permissible limits. However, As and Hg remained lower than the international guidelines for sediments. Cd showing the higher levels in edible tissues may produce toxic effects in the fish and its consumers, therefore, it is not safe to consume these studied fish species from Head Punjnad. Novelty Statement | This investigation highlights the occurrence of Cd, Hg and As at the higher levels in water samples, while As and Hg persisted lower than the international guidelines for riverine sediments at Head Punjnad. The higher levels of Cd in edible fish tissues alluded that it is not safe to consume fish from Head Punjnad.., Irfan, Shahid, M.T. and Afzal, G. 2020. Toxic trace metals assessment in selected organs of edible fish species, sediment and water in head Punjnad, Punjab, Pakistan. Punjab Univ. J. Zool., 35(1): 43-50. https://dx.
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Arsenic (As), mercury (Hg) and cadmium (Cd) are one of the greatest threats to aquatic biota for their persistence, bioaccumulation and biomagnification across the globe. This study presents the first hand data of toxic trace metals in edible fish muscles, sediments and water sampled from Head Punjnad (HP), Pakistan during 2017. The likely reason for the selection of HP as a study target was its emergent prominence as an irrigation hub and holidaymakers spot largely for angling and feasting. The investigated five fish species are Ctenopharyngodon idella, Oreochromis niloticus, Eutropiichthys vacha, Rita rita and Sperata sarwari. The results divulged the pattern of metals concentration in fish in the order of Cd > As > Hg. However, R. rita, O. niloticus and C. idella showed higher accumulation of the metals that clearly alluded to species-linked metal bioaccumulation, which might be due to their unique feeding mood. Cadmium presence ranged between 0.04 – 1.12 ppm while As and Hg fluctuated between 0.01 – 0.04 and 0.001 - 0.18 ppm, respectively. Conversely, higher bioaccumulation was detected in gills rather than the muscle tissues that evidently indicated gradual water quality degradation conceiving higher metal concentrations in the environment. Similarly, a higher concentration of Cd was observed in water (0.78 ppm) and sediment (0.64 ppm) samples. In acquiescence to the above-given outcomes, the metal concentration hierarchical arrangement in sediment and water was identical to the witnessed in fish species (Cd > As > Hg). In conclusion, this study established that selected metals level in HP water and sediments displayed levels higher than the permissible limits. However, As and Hg remained lower than the international guidelines for sediments. Cd showing the higher levels in edible tissues may produce toxic effects in the fish and its consumers, therefore, it is not safe to consume these studied fish species from Head Punjnad.
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Methods for analysing fish stomach contents are listed and critically assessed with a view to their suitability for determining dietary importance—this term is defined. Difficulties in the application of these methods are discussed and, where appropriate, alternative approaches proposed. Modifications which have practical value are also considered. The necessity of linking measurements of dietary importance to stomach capacity is emphasized and the effects of differential digestion upon interpretation of stomach contents outlined. The best measure of dietary importance is proposed as one where both the amount and bulk of a food category are recorded.