The efficiency of a modified flow-through system in lethal and inserting accumulation of naphthalenes (NAPs) in Penaeus monodon muscle in a sublethal toxicity test of crude oil were studied. Subsequently, an analytical protocol to get the. most bioavailable and toxic components of crude oil produced by the system were established. In this system a circulating pump was used to disperse the continuous flow of crude oil and seawater in a mixing chamber connected to two oil-water separating chambers, before flowing to the test tanks. Results of the tissue and water analysis were assayed by gas choromatograph (GC) and gas choromatograph and mass spectrometer (GC-MS). The system kept the level of water soluble fractions of crude oil (WSFCQ) with maximum coefficient of variation as 12.55% for the aliphatic and 11.34% for aromatic components. The system was able to produce 20.166 ppm as the mean of WSFCO in the lethal toxicity test. In the sublethal study it produced 0.129 ppm as the mean of NAPs in the seawater which caused a mean accumulation of 0.945 mg NAPs in 109 muscle wet weight of the test animal at 96 h post exposure by regulating the volume of the oil added into the system. The system also kept the water quality requirements for the test animal during the lethal and sublethal toxicity tests.