Used engine oil pollution has become very common worldwide and particularly in more advanced and affluent countries. Used engine oil is spent, contamination product from used mineral-based crankcase oil, often referred to as waste engine oil. It has been known to cause harm to both aquatic and terrestrial organisms. Large quantity of used engine oils from different sources such as vehicles and engines, hydraulic systems and minor industrial applications [1] is disposed of as harmful waste to the environment. Exposure to used engine oil is directly by absorption or indirectly by altering the physiochemical properties of the water to such an extent that the survival of the organism is threatened [2,3].

Used engine oils contain Poly Aromatic Hydrocarbons (PAHs) and heavy metals like chromium, copper, nickel, lead, iron, silicon etc. which are not detected in new engine oil and increases rapidly in concentration as its uses increases. Used engine oil is harmful to aquatic life. The presence of used engine oil in water reduces aeration propensity [3] leading to an anaerobic condition. 

According to a research by Satyanarayan et al. [4], used engine oil causes erratic swimming in fish and become lethargic at higher concentrations. Also, the study by Ugwu et al. [5] and Oluah [6] showed that high concentration of used engine oil increases mortality rate in fish. Adverse effects of used engine oil might trigger physiological responses reflected in growth performances, haematological parameters and other biomarkers [6].

Though, engine oil is crucial to the modern society, its effect after use poses risks as it is hazardous to the environment. Used engine oil disposal into the aquatic environment, gutters, farms and water drains, not only contaminate water but is also harmful to aquatic life. Its toxicity creates series of environmental problems.

Clarias gariepinus (African catfish) is a fresh water fish species that is very suitable for commercial and small scale farming it can reproduce effectively in captivity and have a good feed conversion ration under favourable condition. It originated from Africa and it’s a good source of animal protein.

Clarias gariepinus can be affected by used engine oil such that its growth performance may be destructed due to heavy metals contained in used engine oil. thus, the need to evaluate the risks or effect of used engine oil on the growth of African catfish is essential.       

The experiment was carried out in the laboratory using fifty (50) juveniles of Claria gariepinus of mean weight (83±0.89g) (Table 1) and mean length (10±0.19cm) bought from African Regional Aquaculture Centre (ARAC) Farm in Aluu, Rivers State. Used engine oil was collected from different mechanic workshops at Ikoku metropolis and tests were carried out by using different concentrations of used engine oil (2, 4, 8 and 16 mL/L) placed in different tank to determine the suitable range that will affect the growth of C. gariepinus juveniles while the uncontaminated water served as control (at 0.00 mL/L).

The fish were fed at 5% of the body weight twice daily, for thirty (30) days. They were measured and weighed after every 7days and mortality assessment was carried out every 24hours for the duration of the experiment. Growth performance indices were calculated as described by Sveier et al. [7]. Also, physico-chemical parameters of the water sample such as temperature, Dissolved Oxygen (DO) and pH of each tank were measured regularly during the experiment.

Data analysis was reported in mean ± SEM using one way Analysis of Variance (ANOVA). The level of significance used was at p-value ≤0.05.

From the experiment carried out, it was deduced that used engine oil can impede the growth of the test fish (Clarias gariepinus). While the control tank increased in weight rapidly, the tank exposed to 2, 4, 8 and 16mL/L of used engine oil decreased in weight from week 1 to week 5 respectively. The results from the growth performance indices showed that exposure of C. gariepinus juveniles to varying concentrations caused mortality with its highest at 60% in 16mL/L of used engine oil and decreased with its decreasing concentration of 40% in 8 and 4mL/L and 20% in 2mL/L. There was no mortality recorded in the control tank.

The Mean Weight Gain (MWG) and Percentage Weight Gain (PWG) reduced with increasing concentration of used engine oil from 2.42g and 8.97% in 2mL/L, to 2.20g and 7.40% in 4mL/L, 1.64g and 5.47% in 8mL/L and to 1.48g and 4.93% in 16mL/L respectively. The control had the highest MWG and PWG of 4.98±0.21g and 16.6±3.12% respectively. Feed conversion ratio was highest in fish exposed to 16mL/L and lowest in the control (Table 2).

Also, from the result, the highest mean water temperature was 28°C analysed in the tanks exposed to 4, 8 and 16mL/L whereas tanks exposed to 2mL/L and the control had the lowest mean water temperature of 27°C. The DO in tank exposed to used engine oil decreased with increased concentrations, while the control tank recorded highest value of DO. The pH range increased with decrease in the concentration of used engine oil, with the lowest value of 5.7 in tank containing 16mL/L, while the control tank had the highest value of 6.9 (Table 3).

The results obtained from this study showed that used engine oil is toxic to C. gariepinus with increasing effects in a dose dependent fashion. In the study, percentage mortality increased from 20% to 60% with increase in used engine oil (2mL/L to 16mL/L) as compared to the control without mortality, this is similar to the study by Fakolujo et al. [8]. The Mean Weight Gain (MWG) and Mean Daily Weight Gain (MDWG) in the result was higher in the control and reduced with increase in the concentration of used engine oil, this was also similar to the study carried out by Achudume [9] there was no significant differences (p>0.05) in the MWG.

Table 1: Mean Weight for the Period of 30 Days (Values are Mean ±SEM) 

Table 2: Mean Growth Performance Indices of Clarias gariepinus Exposed to Different Concentration of Used Engine oil for 30 Days (values are Mean±SEM)

TFI Total Feed Intake, L_{i =}Initial Length, L_{f =} Final LENGTH, Wⁱ = mean initial weight, W_f mean final weight MWG = Mean Weight Gain, MDWG = Mean Daily Weight Gain, PWG = Percentage Weight Gain FCR = Feed Conversion Ratio

Table 3: Mean Dissolve Oxygen, pH and Temperature During the Culture Period

In the research done, the mean water temperatures in all treatments range between 27ºC to 28ºC and was compared to the study by Ruhana et al. [10] whose values were 25.8ºC to 27.5ºC and considered as suitable temperature for C. Gariepinus to survive. The African catfish has an optimal temperature which varies from 20ºC to 30ºC with 25ºC and 27ºC as the most favourable for its adults and juveniles Elnaly et al. [11] though, juvenile fish prefer warmer water temperature than adult fish Sigurd et al. [12].

The mean of DO values recorded in this work ranged between 2.23 mg/L to 3.68 mg/L which indicated low dissolved oxygen for optimum fish growth (Table 3). Fish grow very fast, convert feed efficiency and are healthiest at DO concentrations above 5mg/L [13] Boyd [14] the mean of pH from the result ranged from 5.7 to 6.9 which is considered as an optimum range for most fish species Ajiboye et al. [15] the pH of the water was lowered with increasing concentration of used engine oil, hence, could lead to a stressful environmental condition. On the fish.

This research work demonstrated that aquatic contamination or pollution with used engine oil can affect the growth performance of Clarias gariepinus due to heavy metal present. From the result obtained, it can be said that used engine oil contribute or cause high mortality rate in Clarias sp juveniles with increased concentrations. also, as seen in the result, the water quality especially DO was decreased, this shows that water contamination with used engine oil is not suitable for the survival of Clarias sp.

Therefore, it can be concluded that used engine oil as low as 2mL/L is capable of becoming destructive to C. gariepinus growth, human health and the environment in general. It is therefore recommended that used engine oil impact should be reduced by minimizing its use, practicing proper disposal, establishment of laws and policies to guide its disposal and enlightenment of the inhabitants living around the polluted areas to ensure safety of marine organisms, food security, prevention of death of both animals and humans and the environment as well.

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