Abstract:
A study of effects of salinity and concentrations of water soluble fraction (WSF) of Dubai crude oil on black tiger prawn Penaeus monodon postlarvae was divided into 2 processes; acute toxicity testing and sublethal toxicity testing. The purpose of acute toxicity testing is to determine LC50 of WSF to P.monodon after exposure of 24, 48, 72 and 96 hrs. The level of WSF concentrations (100%, 75%, 50% and 25% of WSF) and salinity (14, 21, 28 and 35 ppt.) were used for LC50 determination. Sublethal toxicity testing was done at 4 levels of salinity (14, 21, 28 and 35 ppt.) and 4 levels of WSF concentrations (0, 20, 40 and 60 ug/l) by a completely randomized design involved factorials. Penaeus monodon were acclimated for a week before testing. In acute toxicity testing, 96-hr LC50 of WSF of Dubai crude oil on P.monodon at salinity 14, 21, 28 and 35 ppt was 81.55, 13.56, 40.65 and 80.05 ug/l, respectively. In the sublethal testing, there were interaction between salinity and concentrations of WSF on oxygen consumption rate, ammonia excretion rate and feeding rate. The highest oxygen consumption rate was 0.008+_0.005 mg O2/gdw/hr found in postlarval shrimp at salinity 14 ppt. and the lowest oxygen consumption rate 0.007+_0.006 mg O2/gdw/hr was found at salinity 35 ppt. Ammonia excretion rate was the highest in salinity 14 ppt., 1.5666+_1.222 mg NH3/gdw/hr and the lowest ammonia excretion rate was 0.932+_0.671 mg NH3/gdw/hr at salinity 28 ppt. Feeding rate was highest at salinity 14 ppt. and lowest at salinity 35 ppt. (0.809+_0.248 mg dry weight Artemia/gdw/hr and 0.354+_0.108 mg dry weight Artemia/gdw/hr, respectively). For different concentrations of WSF, the feeding rate of P.monodon was found the highest value in WSF concentration 20 ug hydrocarbon/l (0.543+-0.285 mg dry weight Artemia/gdw/hr) and the lowest in 0 ug hydrocarbon/l (0.422+_0.137 mg dry weight Artemia/gdw/hr), respectively. The result indicated that total energy of prawns received from food wasmainly deplenished in respiratory and excretory rather than growth in contamination environment, so that scope for growth (SFG) was lower than zero
