HISTOPATHOLOGY STUDIES OF SELECTED ORGANS OF Hemichromis fasciatus INHABITING IGUN GOLD MINING AND OPA RESERVOIRS, OSUN STATE, NIGERIA: A COMPARATIVE STUDY

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INTRODUCTION
The Cichlid, Hemichromis fasciatus (Peters 1857) commonly called banded jewel fish is an ornamental fish which occurs in various freshwater bodies in Africa. An increased pollution of the aquatic environment has caused severe alterations of tissues and organs in aquatic organisms (Mazonet al.,1999). The authors are of the view that in a disturbed environment, especially where pollutants occur in chronic and sublethal concentrations, changes in the structure and function of aquatic organisms are more frequent than mass mortality. Poleksic and Mitrovic-Tutundzic (1994) noted that one of the possible methods of evaluating the effects of pollutants in fish is to examine their organs for morphological changes. Raskovic (2010) reported that fish can be used to evaluate the health of aquatic ecosystems because contaminants build up in the food chain and are responsible for adverse effects and death in the aquatic systems.
Also, studies carried out on various fishes have shown that heavy metals altered the physiological activities and biochemical parameters in organism tissues as observed by Popov et al. (2002), Golovanova (2008), Mary et al. (2015). The toxic effect of heavy metals in fish includes bioaccumulation, histopathological changes in tissues as reviewed by Usha Rani (2000); Adami, et al. (2002) andSehar et al. (2013 Similarly, histopathological changes have been widely used as bio-indicators in evaluating the health of fish exposed to contaminants, both in the laboratory and field studies. Hence, histopathological alterations can be used as indicators for monitoring the effects of various anthropogenic pollutants on organisms and are a reflection of the overall health of the entire population in the ecosystem as reported by Mohammed (2009). Drishya et al. (2016) stated that one of the advantages of using histopathological bio-indicators in environmental monitoring is that this category of bio-indicators allows examining specific target tissues which includes: gills, kidney and liver that are responsible for vital roles. These functions are respiration, excretion and the accumulation and biotransformation of xenobiotics in the fish.
Furthermore, the alterations found in these organs are normally easier to identify than functional ones (Karthigayaniet al. 2014) and serve as warning signs of damage to animal health (Hinton and Laurén 1990).
According to Yildizet al. (2010), increasing exposure to toxic elements in fresh water organisms such as fish and river birds which are often used to monitor the presence of contaminants can have adverse toxicological effects.
Available records have shown that fish species in Igun reservoir bioaccumulated more heavy metals compared to fish species in Opa reservoir (Lawal and Komolafe 2012; Olabanji and Oluyemi, 2014).
This study therefore aims to compare histopathological alterations in the gills, fillet and liver of Igun and Opa reservoirs.

STUDY AREA
The study areas are abandoned gold mine reservoir at Igun village in Atakunmosa West Local Government area of Osun State and Opa freshwater reservoir at Ife central Local Government area of Osun State. The abandoned gold mine reservoir extends over longitude 004030E-004045E and latitude 07035N-07038N. Streams such as Oika, Eleripon and Osun which serve the community were impounded to form reservoirs in order to meet the mining needs of the Nigerian Mining cooperation which started in December 1941.
The second study area which is Opa reservoir is located in Ile-Ife, Osun State, Nigeria. Opa reservoir was impounded in 1978. The major tributaries are rivers Opa, Obudu and Esinmirin. The reservoir has a catchment area of about 116km. The reservoir extends over latitudes07 0 21'N and07 0 35'N and longitudes004 0 31'E and 004 0 39'E (figure 1).

COLLECTION OF FISH SAMPLES
Fish samples were collected on a monthly basis using gill nets, cast net. They were identified using standard keys prepared by Paugy, et al. (2003) and Adesulu and Sydenham (2007). Samples of fish caught were put in a container filled with the reservoir water and dissected in situ.

PREPARATION OF FISH TISSUES AND ORGANS FOR HISTOLOGICAL ANALYSIS
Each fish specimen was split open anteriorly from the anal pore to the pectoral fin to remove its liver, while the gills were removed from the head region. A piece of fillet was also taken just above the lateral line and before the dorsal fin. Each fish gill, fillet and liver were put in a separate well labelled bottle, fixed in 5% formalin for at least 48 hours and transferred into a sampling bottle rack. The method of Bernetet al. (1999) was used for tissues processing for histological studies, the tissues were removed from the fixative, and samples of tissue were rinsed in tap water for 5 minutes, dehydrated in ascending ethanol concentrations (70%, 80% and 90% alcohol) for minimum of 2 minutes, cleared or infiltrated in a wax miscible agent (xylene)for 2 minutes and then embedded in paraffin using standard protocols. The fish tissues were then cut into sections of approximately 5 µm thickness from the block using a rotary microtome (Yamato Kohki, Serial no: 75010JO). The cut samples were dried in a hot air oven to remove moisture and each section were mounted on a glass slide. The sections were de-waxed in a wax-miscible agent, rehydrated through descending concentrations of ethanol (90%, 80% and 70% alcohol) for at least 2 minutes. The sections were then stained with haematoxylin and eosin (Bancroft and Cook 1994), in which the tissues were place in haematoxylin solution for 3 minutes and aqueous eosin for 3 minutes, mounted on a slide and covered with coverslip and labelled appropriately. The tissues were examined, and microphotographs taken using a digital binocular compound LED microscope (model MD827S30L series).

DISCUSSION
The gills of a fish play a vital role in maintaining of aquatic organism ionic homeostasis (Evans, 1993). Subsequently to Al-Mansoori (2006). The histopathological alterations in this organ are a response to exposure to non-specific pollutants (Au, 2004).
Also, atrophy and splitting of muscle bundles revealed in the fillet of H. fasciatus in Opa and Igun reservoirs was likewise recorded by Ramesh and Nagarajan (2013) in the muscle of Clarias batrachus. The degeneration of muscle bundles seen in the fillet of H. fasciatus in Opa reservoir was also reported by Kaoud and El-Dahshan (2010) in the muscle of O. niloticus. It can thus be suggested that different alterations observed in the fillet of H. fasciatus in Opa and Igun reservoirs could be due to the presence of various contaminants in the reservoir.
Histopathological alterations observed in the liver of H. fasciatusin both reservoirs were similarly recorded by Chavan and Muley (2014) in the liver of Cirrhinus mrigala. These lesions are hepatopancreas degeneration, splitting at the wall of central vein, degeneration of liver cells and nucleus hypertrophy. It seems possible that these alterations are due to heavy metals pollution in the two reservoirs. Furthermore, hepatopancreas degeneration observed in the liver of H. fasciatus in Opa reservoir was similar to the report of Naeemi et al. (2013)

CONCLUSION
The results of this study have shown that more alterations were found in the tissues of H. fasciatus in Igun reservoir compared to Opa reservoir. The evidence from this study suggests that bioaccumulation of heavy metals in the tissues of fish from Igun reservoir could have resulted in severe changes in the tissue.