Impaired growth and erythrocyte nuclear lesions of immature Oreochromis niloticus exposed to waterborne crude oil: Persistent responses
S.H.N.P. Gunawickrama, P.D.S.M. Panawala, K.B.S. Gunawickrama*
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.
Keywords: Aquatic pollution; chronic toxicity; ENA; fish growth; head-kidney erythrocytes.