1
Acute Toxicity of copper and mercury to different life stages of
the Nile Tilapia (Oreochromis niloticus)
Acute Toxicity of copper and mercuryto different life stages of the Nile Tilapia (Oreochromis niloticus)
Khalid M. El-Moselhy, Lamiaa I. Mohamedein andMahmoud A. Abdelmoneim
National Institute of Oceanography and Fisheries
ABSTRACT
Tilapia is the most economically important farmed fish in the world and consequently in Egypt. The present study aimed to estimate 96hLC50s of Cu and Hg on four different fish life stages (larva, fry, juvenile and fingerling ) of the Nile tilapia Oreochromis niloticus as a first step of studying their physiological and environmental impacts. The values of 96h LC50s of Cu to these four fish life stageswere 0.81, 0.85, 0.80 and 1.09 ppm, respectively, while for Hgwere 0.20, 0.40, 0.82 and 1.17 ppm, respectively. The toxicity experiments indicated that Hg is more toxic than Cu during the 1st two life stages, where they recorded the same toxicity during the last two life stages with slight increase of Cu toxicity at the last stage. In conclusion, the toxicity tended to elevate with decreasing fish size. Accordingly, the water used in fish farms must be received from controlled source.
Keywords: Toxicity, Cu, Hg, Fish, Oreochromis niloticus, larval stages, larva, fry, juvenile and fingerling.
1
Acute Toxicity of copper and mercury to different life stages of
the Nile Tilapia (Oreochromis niloticus)
INTRODUCTION
Aquatic environments are important biotopes that should be controlled sensitively because of contamination resulting from the industrial, agricultural and anthropogenic activities. Metals are able to disturb the integrity of the physiological and biochemical mechanisms in fish that are not only an important ecosystem component but also used as a food source (Hogstrandet al., 1999; Basha and Rani, 2003).
Many metals are essential to living organisms but some of them are highly toxic or become toxic at high concentrations. Fe (haemoglobin), Cu (respiratory pigments), Zn (enzymes), Co (Vitamin B12), Mo and Mn (enzyme) and light elements(Na, K Ca) play important biological roles in the marine organisms. Transition metals Fe, Cu, Co and Mn which are essential but may be toxic at high concentrations. Metals such as Hg, Pb, Sn, Ni, Se, Cr and As are generally not required for metabolic activity and are toxic to living organisms at quite low concentrations (Forster and Whittmann, 1983; Meria, 1991;Valavanidis and Vlachogianni, 2010).It is known that increasing the amount of Hg in the human tissues can cause Minamata disease,while copper can cause Wilson’s disease (Moore, 1991).
Increasing the importance of fish as a food source expands the interest of studying the trace metals accumulation in its tissues. Since it is often at the top of the aquatic food chain and may concentrate large amounts of metals from water. As well as,fish has been used extensively in aquatic toxicology studies (Rougier et al., 1996; Dethloff et al., 1999; McGeer et al., 2000; Beaumont et al., 2000; Kamunde et al., 2002; Bury et al., 2002).
The main objective of ecotoxicology is the evaluation of risk for anecosystem exposed to environmental stress, including contamination (Ferrer et al. (2006).
There are extensive regulatory requirements for fish acute toxicity data in support of both environmental risk assessment and also hazard classification (Braunbeck and Lammer, 2006). Tilapia is a common species around the world and had been used to evaluate the environmental hazards in its habitats. Straus (2003), Karasu Benlü and Köksal(2005), Ishikawa et al. (2007), Ezemonye et al. (2008) andKarasu Benlü et al, (2009) studied the toxicity of different types of contaminants on tilapia. In Egypt, Abdel-Tawwab and Mousa (2005) studied the effect of calcium pre-exposure on acute copper toxicity to juvenile Nile tilapia, Oreochromis niloticus.
The present study aimsto investigate the LC50of copper and mercury in four life stages of Nile Tilapia, Oreochromis niloticus. This fish species was chosenfor its economic important, easily transported and maintained in the laboratory.
MATERIALS AND METHODS
The fish used in the present experiments (Nile Tilapia, Oreochromis niloticus) werereared in the outdoor pond of NIOF fish farm. Four Different life stages were picked after 3, 15, 45 and 90 days (larvae, fry,juvenileand fingerlings, respectively.) from the hatching. Fish stages and they were transported to the laboratory in containers containing water from the same pond. They have been acclimated for a day in a stocktank. Length and weight for the different fish stages were as follow:
Stage / length (cm) / weight (gm)Larvae
Fry
Juvenile
Fingerling / 0.8- 1.4
1.7-2.5
2.9-3.8
4.0-5.8 / 0.013-0.026
0.058-0.243
0.419-0.90
1.0-2.8
Stock solutions of the heavy metals copper and mercury were prepared by using pure grad ofCuSO4.5H2O and HgCl2 .During the experiments, test solutions of copper and mercury were freshly prepared from the stock solutions. Test solutions of Cu ranged from 0.5 to 5 ppm, while Hg varied from 0.05 to 2 ppm for all 4 life stages.
The experiments:
Experimental tanks were prepared and filled with 5 liters of water before adding the toxicants. Thirty minutes after adding the toxicants, 20 individuals from each stagewere randomly picked from the stock tank, and introduced to each of the experimental tanksthen experimental time started. Dead fish for each experiment were counted every 8 hours and removed from the tanks. The experiments were terminated after 96 hours. Tanks were cleaned and the experiments were repeated in the same way with a fresh batch of each stage to duplicate and confirm the results. Mortality rate (96 h LC50) was calculated according to Abbott’s formula (Finney, 1971).
RESULTS AND DISCUSSION
Copper
Copper is highly toxic to aquatic organisms and interacts with numerous inorganic and organic compounds which affect its bioavailability and toxicity to aquatic biota. Its toxicity depends on environmental factors that change through time and space (e.g. temperature and water quality) and on the affected organism’s species, age, size, and reproductive condition (Woody, 2007).
Figure (1) shows the toxicity patterns of Cu toNile Tilapia, Oreochromis niloticus, at different life stages (larva, fry, juvenile and fingerling). Estimation of the median lethal con-centrations of Cu showed that the 96h LC50swere 0.81, 0.85, 0.80 and 1.09 ppm, respectively. It can be noticed that the LC50s in the 1st 3 length categories were similar and the 4th category was the highest one which means that the tolerance of fish increases at the 4thlength category than the others, also indicated that the 1st stages were more venerable than the older stages.
Few studies examined the relation between fish size and the copper toxicity forfinfish. Howarth and Sprague (1978) reported that copper toxicity to rainbow trout, Oncorhynchus mykiss, decreased with fish growth, and the toxicity for 0.71 g fish was three times higher than that for 10 g in freshwater.
There were numerous studies examining the Cu toxicity to fresh and marine fish, 96h LC50 reported a range between 3 to 7 ppm and 0.06 to 20 ppm,respectively (Choi and Kinae, 1994; IPC INCHEM, 1998).Straus (2003) recorded a range of (0.18 to 43.06 ppm) within a total alkalinity of 16- 225mg/l CaCO3, and stated that the Cu sulfate can be extremely toxic to fish in water of low alkalinity.In the same manner the mean total alkalinity in the present study condition was 286 mg/l CaCO3. As well as, more studies recorded that Cu is less toxic in hard water than in soft water (Pagenkopf et al., 1974; Andrew et al., 1977; Howarth and Sprague, 1978; Chakoumakos et al., 1979; Miller and Mackay, 1980).
For fresh water fish, Oliva et al. (2009) reported 0.35 ppm Cu as 96h LC50 for juvenile singales, 0.25 for chequered rainbow, 0.14 for black striped rainbow and 0.021 ppm for fly specked hardhead.This indicates that the present studied species was more tolerance to Cu toxicity than other species studied else where.
Mercury:
Mercury is classified as one of the most toxic metals, which are introduced into the natural environment by human interferences (Buhl, 1997). Inorganic mercury is the most common form of the metal released in the environment by industries, presenting a stronger acute effect on fish tissues than that of its organic form (Sunderland and Chmura, 2000).
Figure (2) shows the toxicity patterns of Hg to the different studied fish stages of the Nile Tilapia. 96h Hg LC50 were 0.20, 0.40, 0.82 and 1.17 ppm for larva, fry, juvenile and fingerling stages, respectively. It was found that the toxicity of Hg was significantly decreased (r=0.999, p≤ 0.05) with increasing the fish life stage (Fig. 3). Unlike the present study, some studies on other aquatic fish species indicated that Hg toxicity did not change significantly with varying size (Verma et al., 1985;Thongra-aret al., 2003).
From the previous studies, Ishikawa et al.(2007) recorded 0.22 ppm 96h LC50for Oreochromis niloticusfingerlings which was compare to the present study. In the context, Ramamurthi et al. (1982) recorded Hg LC50 0.739 ppm for Tilapiamossambicus. As well as, many studies recorded a range of 0.057 – 0.198 ppm Hg LC50 for different fish species which was more or less lower than the present study (Buhl, 1997;Shyong and Chen, 2000). It was indicated that the present examined species was more tolerant than the previous studied species.
For both of the present studied metals (Cu and Hg), it can be noticed that the toxicity tended to elevate with decreasing fish size,this mean that the earlier stages were more sensitive than the older one. Grosell et al.(2002) stated that the size was an effective factor for acute toxicity in fresh water organisms. It has been mentioned that small fish or younger organisms were more susceptible to metal poisoning than the larger or more mature fish (Shyong and Chen 2000).Thongra-aret al. (2003) and Furuta et al. (2007)found that theseabass larvae were more sensitive to Hg toxicity than the juvenile stages.
By comparing the toxicity of Cu and Hg in the present study (Fig.3), it can be stated that the Hg is more toxic than Cu during the 1st 2 life stages, where they recorded the same toxicity during the last 2 life stages with slight increase of Cu toxicity at the last stage.Yuan (1994) and Shyong and Chen (2000) found that Cu was more toxic than Hg to Acrosscheilus paradoxus andZaccobarbata,respectively.
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Acute Toxicity of copper and mercury to different life stages of
the Nile Tilapia (Oreochromis niloticus)
Fig. (1): Toxicity of copper to different stages (a: larvae, b: fry, c: juvenile and d: fingerlings) of the Nile tilapia, Oreochromis niloticus.
Fig. (2): Toxicity of mercury to different stages (a: larvae, b: fry, c: juvenile and d: fingerlings) of the Nile Tilapia, Oreochromis niloticus
Fig. (3):Toxicity pattern of copper and mercury to different stages (larvae, fry, juvenile and fingerlings) of the Nile Tilapia, Oreochromis niloticus
سمية النحاس والزئبق على المراحل العمرية المختلفة من أسماك البلطى النيلى
خالد محمد المصيلحى ، لمياء إسماعيل محمدين ، محمود أحمد عبد المنعم
المعهد القومى لعلوم البحار والمصايد، مصر
أسماك البلطي من أهم الأسماك الاقتصاديةالمستزرعةفي العالم وفى مصر. تهدف هذه الدراسةإلىتقدير التركيز النصف مميت خلال 96 ساعة لكلمنالنحاس والزئبقلأسملك البلطيالنيليكخطوة أولىلدراسةتأثيرهماالفسيولوجىوالبيئى.تم فحصالسمية الحادةلكل منالنحاس والزئبقفى أربعمراحل عمرية مختلفة من حياةالأسماك (اليرقة, الزريعة، صغار الأسماك والإصبعيات). أوضحت النتائج أن التركيز النصف مميت خلال 96 ساعة للنحاس كان 0٫81 ، 0٫85، 0٫80 و 1٫09 جزء في المليون، بينماكانللزئبق0٫20، 0٫40 ، 0٫82 ، 1٫17 جزء في المليونعلى التوالي. أوضحت التجارب أن الزئبقأكثر سمية منالنحاسخلال المرحلتين الأولى والثانية من حياةالأسماك، بينما تساوى فى المرحلتين الثالثة والرابعة مع زيادة طفيفة لسميةالنحاس عن الزئبقفي المرحلةالأخيرة من عمر الأسماك. وقد خلصت الدراسة إلى أن السمية لكل من النحاس والزئبق تميل إلى الارتفاع مع تناقصحجم الأسماك، وتبعا لذلك، يجب أنتكون المياه المستخدمة فيالمزارع السمكيةيتم الحصول عليها من مصادرتحت المراقبة والمتابعة حتى نتجنب نفوق الأسماك فى المراحل الأولى من عمرها.