Abstract
Eggs and larvae of Heterobranchus longifilis were exposed to extracts of different concentrations of Nigerian Bonny light crude oil and Exxon Mobil Oso off-shore condensate during a comparative toxicity experiment carried out in the Institute of Oceanography Fish Farm, University of Calabar, Nigeria. Petroleum hydrocarbon was extracted from the two oils in separate 30litre glass aquaria and the eggs and young larvae were contaminated by exposing them to three concentrations of both oils, viz: 101, 103, 102ppm for approximately 10 days. Young eggs seemed to be more sensitive from 5 to 30 hours after fertilization. Extract from 104 ppm of Bonny Light Crude and Oso condensate caused 40% and 30% mortality respectively, after 100h. Embryos contaminated with Bonny Light crude extract did not recover on transfer to clean water. Delayed development was observed in the two-highest concentrations. Heterobranchus longifilis larvae were found to have a “mean critical time” of 4.2 days in the highest concentration of Oso condensate extract when larval integument was damaged. It is concluded that Bonny light crude could be a more dangerous pollutant to juvenile fish than the Oso condensate. KEYWORDS: Heterobranchus longifilis , crude Oil extracts, Mortality, Bonny Light Crude, Exxon Mobil Oso Condensate.
Highlights
The marine environment adjacent to the Nigerian Gulf of Guinea is impregnated with a galaxy of oil rigs, flow stations and other petroleum based installations
The present investigation compares the toxicity of oil condensate from Exxon-Mobil Oso rig and the Bonny Light Crude on the early egg and larval stages of the African catfish (Heterobranchus longifilis) which is highly priced in West African countries
The amounts of Bonny light crude oil and Oso condensate used for preparing the extracts, is not a criterion for the actual amount and types of dissolved hydrocarbons
Summary
The marine environment adjacent to the Nigerian Gulf of Guinea is impregnated with a galaxy of oil rigs, flow stations and other petroleum based installations This has resulted in oil entering the marine and adjoining estuarine waters from time to time. Water extracts of different concentrations of crude oil have been reported to show high toxicity on herring eggs when incubated under 103 and 2.104ppm with a mean survival time of 2.5 to 3.5 days (Kuhnhold, 1982). This high toxicity is mainly caused by low boiling components of petroleum hydrocarbons. The present investigation compares the toxicity of oil condensate from Exxon-Mobil Oso rig and the Bonny Light Crude on the early egg and larval stages of the African catfish (Heterobranchus longifilis) which is highly priced in West African countries
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