Eco-physiological impact of commercial petroleum fuels on nile tilapia, oreochromis niloticus (L.)
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ECO-PHYSIOLOGICAL IMPACT OF COMMERCIAL PETROLEUM FUELS ON NILE TILAPIA, OREOCHROMIS NILOTICUS (L.) Safaa M. Sharaf 1 and Mohsen Abdel-Tawwab 2*1 Department of Animal Production and Fish Wealth, Faculty of Agriculture, Suez Canal University, Ismailia, Egypt. 2Department of Fish Biology and Ecology, Central Laboratory for Aquaculture Research, Abbassa, Abo-Hammad, Sharqia 44662, Egypt. * Corresponding author email: mohsentawwab@yahoo.com Abstract The pollution of commercial petroleum fuels (CPF) is one of the environmental constrains that produces aqua-toxicological effects, which are deleterious to aquatic life. Therefore, this study was conducted to explore the effect of some CPF; kerosene, gasoline or diesel, on the performance of Nile tilapia, Oreochromis niloticus (L.). Healthy fish (49.5±1.3 g) were distributed into glass aquaria and 12 ml of kerosene, gasoline, or diesel were separately added to 6 120-L aquaria. Fish were stocked into the aquaria containing kerosene, diesel, or gasoline for 5 minutes. Signs of poisoning in fish exposed to each fuel type included air gulping, increased opercular movement, and dyspnea. Fish lost their balance, meanwhile no poisoning signs were observed in control fish. At 0, 1, 2, 3, and 4 weeks of the recovery, blood samples were taken to measure the different physiological variables. At the end of this experiment, fish were collected, counted and weighed. Fish in control group grew gradually up to the end of the experiment, meanwhile fish exposed to kerosene, diesel, or gasoline lost their weights for 2 weeks and started to grow again. Moreover, weight gain and SGR of fish exposed to diesel and gasoline were less than that exposed to kerosene. Feed intake, FCR, and survival rate of the exposed fish were poor. RBC count and Hb in fish exposed to kerosene, diesel, or gasoline increased by time and the maximum count was obtained at the 1st week; their values decreased gradually up to the 4th week. Glucose level was maximized after the exposure to kerosene, diesel, or gasoline and decreased gradually up to the end of the experiment. Plasma lipids increased significantly by time at the treated fish groups. Plasma protein in fish increased suddenly after the exposure to kerosene, diesel, or gasoline and it decreased by time to be close to that of control group. AST and ALT activities in fish increased gradually after their exposure to CPF and the maximum values were obtained after 3-4 weeks. The lowest cortisol value was obtained at control, which was insignificantly changed throughout the experimental period. This study has demonstrated that the acute exposure to CPF had a highly significant effect of reducing the growth performance of Nile tilapia and affected their physiological status. INTRODUCTION The majority of studies examining the toxicity of petroleum hydrocarbons have focused on marine species, thus the toxic effects of petroleum hydrocarbons on freshwater species are relatively unknown. The main source of freshwater environments contamination by commercial petroleum fuel (CPF) is runoff from urban, industrial, and agricultural industries. The mining of oil shale reserves may also pose a risk to freshwater ecosystems. Currently, leakage of oil transport pipelines, storage tanks, and accidents involving petroleum transport vehicles are contributors to hydrocarbon pollution in the freshwater ecosystem. Oil pollution is one of the environmental constrains that produces aqua-toxicological effects, which are deleterious to aquatic life (Kori-Siakpere 2000; Agbogidi et al. 2005). A variety of pollutants including crude oil and its products are known to induce stress conditions, which impair the health of fish (FEPA 1991). Ekweozor (1989) reported that frequent spillages of crude oil and its products in creeks and rivers may have resulted in a marked reduction in the number of both freshwater and marine creatures. Earlier reports have also shown that oil pollution impact negatively on fishery resources (Kilnhold 1980; Afolabi et al. 1985). Ajoa et al. (1981) and Azad (2005) observed that eggs and young stages (fingerlings) of fishes are especially vulnerable to the toxic effects of crude oil and its refined products. The eco-physiological effects of crude oil on Machaerium lunatus had also been reported by Bamidele and Agbogidi (2006). Nile tilapia, Oreochromis niloticus (L.) are native to Egypt and are worldwide distributed (El-Sayed 2006). This species has been used previously in laboratory studies and has been shown to be a suitable organism for monitoring the effects of xenobiotics. This study used Nile tilapia as a model to measure the potential toxic effects of cCPF on fish performance and to test the ability of this fish species to recover from the exposure effect. Therefore, the present study has been undertaken to evaluate the physiological alterations of Nile tilapia following the acute exposure by kerosene, gasoline, and diesel. MATERIALS AND METHODSFish culture regime The experiment design was factorial, including CPF and time intervals. Healthy Nile tilapia, O. niloticus (L.), were obtained from the nursery ponds, Central Laboratory for Aquaculture Research, Abbassa, Abo-Hammad, Sharqia, Egypt. Fish (49.5±1.3 g) were acclimated in indoor tanks for 2 weeks by feeding a commercial diet containing 20% crude protein (CP). After that they were distributed into eight120-L glass aquaria at a rate of 15 fish per aquarium, which was supplied with compressed air from air pumps via air-stones. Kerosene, gasoline, and diesel were brought from a commercial gas station, and their specific gravities were 740, 700, and 820 g/L, respectively. Twelve mls of kerosene, gasoline, or diesel were separately added to 120-L aquarium and they were vigorously shaken with the aquaria water for 5 minutes. After that, fish were stocked into the aquaria containing kerosene, diesel, or gasoline for 5 minutes. Then, fish were transferred into other 6 120-L aquaria containing dechlorinated tap water over 4 weeks for recovery where each treatment was represented by 2 replicates. In control group, fish were not exposed to any fuels. The blood samples were taken; from 3 fish per each aquarium, within one hour of the end of the exposure to represent zero time sample. At 1, 2, 3, and 4 weeks of the recovery period, blood samples from 3 fish per each aquarium were taken to measure the different physiological variables. During the recovery trial, fish were fed on 25% CP up to satiation twice daily at 9:00 and 14:00 h for 6 days a week. The amount of the given feed for each aquarium, calculated as a summation of given diets during the experimental period, was subsequently taken to represent feed intake. Fish in each aquarium were weekly group-weighed and dead fish were removed and recorded daily. A three quarter of each aquarium's water with fish excreta was siphoned every day and replaced by well-aerated water provided from a storage fiberglass tank. Water quality measurementsWater samples were collected weekly at 15 cm depth from each aquarium. Dissolved oxygen (DO) and water temperature were measured in situ with an oxygen meter (YSI model 58, Yellow Spring Instrument Co., Yellow Springs, OH, USA). Unionized ammonia was measured using DREL/2 HACH kits (HACH Co., Loveland, CO, USA) and pH with a pH meter (Digital Mini-pH Meter, model 55, Fisher Scientific, Denver, CO, USA). In all treatments, DO concentrations ranged from 4.1 to 4.6 mg/L, water temperature average was 26.5±0.8 oC. Unionized ammonia ranged from 1.2 to 1.6 mg/L, and pH value ranged from 7.2 to 7.6. All the water quality parameters were within the acceptable ranges for fish growth (Boyd 1984). Fish performanceAt the end of this experiment, fish were collected, counted and weighed. Growth performance was determined and feed utilization was calculated as following: Specific growth rate (SGR; %/day) = 100 (ln W2 – ln W1) / T; where W1 and W2 are the initial and final weight, respectively, and T is the number of days in the feeding period; Feed conversion ratio (FCR) = feed intake (g) / weight gain (g).
At sampling date fish were not fed during the 24 h immediately prior to blood sampling. Three fish from each aquarium were anaesthetized with buffered tricaine methane sulfonate (20 mg/L) and blood was collected from the caudal vasculature. The extracted blood was divided in two sets of Eppendorf tubes. One set contained 500 U sodium heparinate/mL, used as an anticoagulant, for hematology (hemoglobin and red blood cell counting). The second set, without anticoagulant, was left to clot at 4 oC and centrifuged at 5000 rpm for 5 min. at room temperature. The collected serum was stored at –20 oC for further assays. Red blood cells (RBCs) were counted under the light microscope using a Neubauer haemocytometer after blood dilution with phosphate-buffered saline (pH 7.2). Hemoglobin (Hb) level was determined colorimetrically by measuring the formation of cyanomethaemoglobin according to Van Kampen and Zijlstra (1961). Glucose was determined colorimetrically according to Trinder (1969). Total protein and total lipid contents in plasma were determined colorimetrically according to Henry (1964) and Joseph et al. (1972), respectively. Activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in plasma were determined colorimetrically according to Reitman and Frankel (1957). Plasma cortisol levels were measured by radioimmunoassay as previously validated by Chiu et al. (2003. Statistical analysis Data were analyzed using a two-way ANOVA with fuel sources and time intervals as factors. Statistical significance was set at the 5% probability level and means were separated using Duncan’s(?) new multiple range test. The software SPSS, version 15 (SPSS, Richmond, USA) was used as described by Dytham (1999). RESULTSFish subjected to the kerosene, gasoline, or diesel polluted waters were removed after 5 minutes. During the exposure period to any of the fuels, the air gulping and the increased opercular movement were observed with apparent respiration difficulties. Fish lost their balance, meanwhile no poisoning signs were observed in control fish. Table 1. Growth performance and feed utilization of Nile tilapia exposed to commercial fuels and recovered for 4 weeks.
Means having the same letter in the same row are not significantly differed at P < 0.05. The growth performance of Nile tilapia subjected to acute exposure of any of the tested pollutants was significantly affected (Table 1). Fish in control group grew gradually up to the end of the experiment, meanwhile fish exposed to kerosene, diesel, or gasoline lost their weights for 2 weeks and started to grow again (Fig 1). Moreover, weight gain and SGR of fish exposed to diesel and gasoline were less than that exposed to kerosene; the maximum fish performance was obtained in control fish (P < 0.05; Table 1). Feed intake, FCR, and survival rate of the exposed fish were poor.
Figure 1. The mean values of live body weight (g) of Nile tilapia after short-term exposure to commercial petroleum fuels. Red blood cells count in fish exposed to kerosene, diesel, or gasoline increased by time and the maximum count was obtained at the 1st week; their counts decreased gradually up to the 4th week (Fig 2). Hemoglobin in Nile tilapia was suddenly increased after their exposure to CPF and decreased by time up to the 4th week; they were close to that of control fish (Fig 2). Glucose level was maximized after the exposure to kerosene, diesel, or gasoline and decreased gradually up to the end of the experiment (Fig 3). Glucose levels of treated fish were higher than that of control. Plasma lipids increased significantly by time at the treated fish groups and their values were significantly higher than that of control group (Fig 3). Plasma protein in fish increased suddenly after the exposure to kerosene, diesel, or gasoline and it decreased by time to be close to that of control group (Fig 3).
Figure 2. The mean values of RBCs count (No/mm) and hemoglobin (mg/dL) in Nile tilapia after short-term exposure to commercial petroleum fuels and recovered for 4 weeks.
Figure 3. The mean values of glucose, lipids, and protein (mg/L) in Nile tilapia after short-term exposure to commercial petroleum fuels.
Figure 4. The mean values of AST and ALT activities (mg/dL) in Nile tilapia after short-term exposure to commercial petroleum fuels. Activities AST and ALT increased gradually after their exposure to kerosene, diesel, or gasoline and the maximum values were obtained after 3-4 weeks (Fig 4). The lowest values of AST and ALT were obtained at control group, which did not significantly differ throughout the experimental period. Plasma cortisol in fish was suddenly increased after their exposure to kerosene, diesel, or gasoline (Fig 5); cortisol value was significantly differed by fuel source (kerosene > gasoline > diesel). The lowest cortisol value was obtained at control which was insignificantly changed throughout the experimental period.
Figure 5. The mean values of plasma cortisol (µg/L) in Nile tilapia after short-term exposure to commercial petroleum fuels. DISCUSSIONThe results obtained herein indicated that CPF had negative impacts on the growth performance and survival of Nile tilapia. However, the exposure of fish to these pollutants resulted in reduced feed intake and thus lowered body weight. These results indicate that the exposure to CPF may lead to a reduction in fish appetite or complete fish fasting resulting in lower retention rate of nutrients into fish body and so growth was reduced. The findings of this study agreed with Kicheniuk and Khan (1981) and Kori-Siakpere (2000) who noted that exposure of fish to water soluble fractions (WSF) of crude oil can result in reduced feeding and lower body weight. Dede and Kaglo (2001) reported that the survival of Nile tilapia decreased by increasing concentration of diesel fuel. Ofojekwu and Onah (2002) stated that fish are known to increase their metabolic rates to metabolize and excrete aromatic hydrocarbons and consequently allocate more energy to homeostatic maintenance than storage exhibiting growth retardation. Additionally, delayed growth and reduced survival of pink salmon (Onchorhynchys gorbuscha) embryos has been observed following exposure to crude oil (Heintz et al. 2000). In juvenile turbot study, fish exposed to higher concentrations of the fuel exhibited reduced growth and feed consumption (Saborido-Rey et al. 2007). Fish hypoxia and the increased respiration of fish were observed within few minutes after their exposure to CPF. This result may be because these pollutants have been reported to cause structural damage to the respiratory lamellae of the gills (Poirier et al. 1986; Correa and Garcia 1990; Prasad 1991), as well as to have narcotic actions (Correa and Garcia 1990). Such effects would be predicted to impede gas exchange, and result in hypoxaemia (Perry et al. 1989; Ristori and Laurent 1989; Randall and Perry 1992). Other studies using flounder (Platichtys flesus) found that exposure to the WSF of crude oil caused declines in the plasma oxygen content, suggesting fish were experiencing respiratory problems (Alkindi et al. 1996). In addition, fusion of secondary lamellae, gill hyperplasia, and oedema have been reported in fish exposed to petroleum hydrocarbons (Correa and Garcia 1990; Prasad 1991; Dede and Kaglo 2001).The increase of RBC, Hb, glucose, and cortisol were observed in fish following their exposure to CPF. In this regard, the study of Alkindi et al. (1996) observed that after 3 h exposure of flounder to 50% WSF of crude oil, RBC and Hb increased significantly. Kita and Itazawa (1990), Pearson et al. (1992), and Alkindi et al. (1996) reported that the exposure of fish to petroleum hydrocarbons stimulates the release of catecholamines, which could have a number of potentially beneficial effects, including stimulation of splenic release of erythrocytes to aid O2 carrying capacity, stimulation of Na+/H+ exchange in erythrocytes, and resultant increases in haemoglobin-oxygen affinity. The rise in plasma glucose concentrations indicates a stress-induced mobilization of energy reserves. Some studies suggest that fish exposed to petroleum hydrocarbons have elevated concentrations of plasma cortisol indicating a corticosteroid stress response. In this regard, Alkindi et al. (1996) found that the exposure of flounders to a 50% dilution of the WSF of Omani crude oil, a mix of aromatic hydrocarbons (benzenes, toluene, and xylenes and lower amounts of naphthalenes), resulted in a progressive increase in plasma cortisol concentrations continuing over the 48-h exposure period. Moreover, cortisol has a direct effect on carbohydrate metabolism, stimulating glycogenolysis and gluconeogenesis, but that it also interacts with catecholamines which may exert dominant effects in the immediate stages of stress (Wright et al. 1989; Vijayan and Moon 1994; Vijayan et al. 1994). The fluctuation in plasma lipids, protein, AST, and ALT may be due the disturbance of metabolic pathways. In addition, the increase in AST and ALT activities are indicatives to liver damage, which might have occurred due to the exposure to CPF and hence leading to the leakage of these enzymes into the blood. In this regard, Martin-Skilton et al. (2008) demonstrated that acute exposure of juvenile turbot, Scophthalmus maximus to the Prestige fuel oil elicits alterations in some hepatic biotransformation enzymes with different sensitivities, and leads to decreased levels of testosterone in plasma of juvenile turbot which might threaten reproductive capability of exposed individuals. It is noticed that all variables were declined to be close to those of control group after 2 weeks, except lipids and AST, and ALT need time over 4 weeks to be near those of control group. These results may be because CPF not bioaccumulate in exposed fish, but they are rapidly metabolized to form epoxy- and hydroxyl-derivatives during phase I metabolism and subsequently converted into highly water-soluble conjugates (e.g., glucuronides or sulfates) that are excreted through the bile (Varanasi et al. 1985). Pollino and Holdway (2003) reported that the short-term exposures of petroleum hydrocarbons to rainbowfish at realistic concentrations potentially alter metabolic and detoxification enzymes, with metabolic enzymes recovering after depuration (17 days). Conclusively, this study has demonstrated that the acute exposure to CPF significantly reduced the growth performance of Nile tilapia. The study has also showed that Nile tilapia can serve as a bio-indicator of CPF toxicity. Particular attention should also be given to CPF process aimed at minimizing their toxicity to the aquatic ecosystem.
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