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Feeding habits and trace metal concentrations in the muscle of lapping minnow Garra quadrimaculata (Rüppell, 1835) (Pisces: Cyprinidae) in Lake Hawassa, Ethiopia
Abstract
Diet composition and trace metal concentration in the muscle of the lapping minnow Garra quadrimaculata (Rüppell, 1835) was investigated to study the trophic status of the species as well as to assess the level of bioaccumulation of heavy metals in the body of the fish. The study was conducted based on 328 gut samples collected from February to March (dry months) and from August to September (wet months) of the year 2011. Frequency of occurrence and volumetric methods were employed in this study. Detritus, fish eggs, macrophytes, phytoplankton and insects occurred in 54.9%, 16.2%, 43.9%, 56.4% and 26.6% of the guts, respectively and comprised 27.1%, 22.2%, 18.2%, 18.2% and 14.1% of the total volume of food, respectively. The proportions of different food items consumed varied during the dry and wet months. Fish eggs and detritus were the dominant food items during the dry months. Macrophytes and insects were also common in the diet. During the wet months, phytoplankton was the most dominant food item (33.5% by volume). Macrophytes, detritus and insects were also important in the diet. The mean volume of fish eggs and phytoplankton decreased as the size of fish increased while the contributions of detritus, insects and macrophytes increased with fish size. The present study clearly indicated that G. quadrimaculata in Lake Hawassa is omnivorous in its feeding habits. Out of the seven analyzed trace metals (Cr, Mn, Zn, Cu, Cd, Pb and Ni), Cd, Pb, and Ni were below detection limits. There was a significant difference (p<0.05) between the mean concentrations of Zn and Cr in the muscle of the fish in the dry and wet months. The concentration of Zn in the dry month was significantly lower than its concentration in the wet months (p<0.05). By contrast, the concentration of Cr in the dry months was significantly higher than its concentration in the wet months. There were no significant variations in the concentrations of Mn and Cu between dry and wet months. There was no sign of bioaccumulation of the investigated trace metals as the fish grew older. The detected elements were compared with different standards and found to be below the maximum permissible limits for human consumption.
Keywords: Feeding habits, G. quadrimaculata, Ontogenetic diet shift, heavy metals, Lake Hawassa.
