Crude oil impact studies have largely been limited to marine setting and it hampers the understanding and predictability pertaining to freshwater environments following contamination episodes. Growth and erythrocyte nuclear abnormalities (ENA) were followed in freshwater fish Oreochromis niloticus experimentally exposed to crude oil (Arabian light) dispersed in water. Study comprised of a control (no crude oil in water), and two experimental groups with 5 µL/L and 25 µL/L crude oil dispersed in water (5 ppm and 25 ppm respectively), and involved continuous exposure of fish (35 fish/tank in triplicate) with static renewal over a 90-day period. Growth was estimated serially at 18-day intervals (n=40-60). Both exposure groups reduced (p<0.05) weight-based and length-based growth rates and specific growth rates. Giemsa-stained peripheral blood and head kidney smears on day 90 (n=6) showed increased (p<0.05) micronuclei, nuclear buds, fragmented apoptotic nuclei and other types of ENA frequencies (per 1000 RBC) in the fish exposed to 25 ppm crude oil. Moreover, crude oil induced ENA levels were quantitatively different (p<0.05) between the peripheral blood and head kidney. Results show that crude oil hampers growth and sustains elevated ENA of O. niloticus juveniles in freshwater environment.
Growth and histopathology of juvenile Oreochromis niloticus (L.) was studied upon continuous exposure to contaminated sediments from the maritime fisheries harbour of Galle, Sri Lanka. Sixteen week long experiment comprised of four duplicated groups of fish in freshwater (NC: negative control without sediment, C: control with unit-dose of pristine sediment, T1 with unit-dose of contaminated sediment, T2 with three unit-doses of contaminated sediment) with total renewal of water and sediment on each fourth day serially. Unit-dose of sub-lethal wet sediment was arbitrarily decided as 38ml through a series of tolerance tests. Total length and weight of fish were recorded (n=20x4 per group) initially and on completion of weeks 4, 10 and 16. Gill and liver histology was qualitatively examined using four sacrificed fish per group at termination. Results showed that harbour sediment in water significantly (p<0.05) decreased cumulative growth rates of T1 and T2 fish in terms of absolute growth rate (0.58-0.59 mm/day and 0.17g/day), relative growth rate (1.52-1.56% length gain day-1 and 0.73% weight gain day-1) and specific growth rate (0.89-0.91% day-1 in length, 2.60-2.61% day-1 in weight) as compared to C and NC groups. T1 and T2 juveniles developed toxicopathic signs in gill (lamellae-fusion, decreased inter-lamellar space) and in liver (extensive necrosis, hydropic vacuolation). Growth parameters remained similar between C and NC groups throughout the study with no histological alterations suggesting that sediment borne salinity had no differential effect across groups. This study shows that exposure to contaminated sediment from Galle fisheries harbour causes growth reduction and pathologic lesions in gills and liver of O. niloticus juveniles. DOI: http://dx.doi.org/10.4038/jur.v2i1-2.7850 J. Univ. Ruhuna 2014 2:14-23
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