ASPECTS OF REPRODUCTIVE BIOLOGY AND ABUNDANCE OF AFRICAN BONYTONGUE (HETEROTIS NILOTICUS) IN GREAT KWA RIVER, NIGERIA

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INTRODUCTION
The Great Kwa River in recent times has witness a significant increase in human activities which had traditionally centred on artisanal fisheries, aquaculture and small-scale farming along the coastal regions. The Great Kwa River is one of the tributaries of the Cross River Estuary and its basin has undoubtedly influenced by urban development especially the increasing numbers of houses and factories built around the freshwater and mangrove swamps of the river, the expansion of the University of Calabar which has almost encroach into the river floodplain.
Agricultural farms are the primary engagement witnessed at the coastal regions of the Great Kwa River. The surrounding mangrove vegetations have suffered human interferences resulting in breeding ground and habitat loss, degradation and undoubtedly many fish species including Heterotis niloticus are threatened and endangered Mustapha (2010). Due to general environmental degradation which includes oil spillages, pollution and destruction of mangrove swamps, this species has lost an estimated 60% of its previous breeding and nursery habitat in Nigeria with subsequent reduction in populations (Bake & Sadiku, 2005;Offem et al., 2011).
Heterotis niloticus has no origin in Great kwa rather was introduced by escaping from a flooded pond in Cameroon into the wild (Ekanem, 2000) and spread into Cross River State and Akwa Ibom State in Nigeria. The size and flesh of this fish species attracts fishers, aquaculturist and consumers.
The African bony-tongue is one of the accepted food fish species in Nigeria inland waters. It may be due to the firmness in the flesh texture and the large size. This species is widely distributed in rivers, creeks and freshwater lakes of Western and Central Africa (Levêque et al., 1990). In Cross River Basin highest body weight that has been recorded is 8kg and length of 1.2 meters, but the highest length and weight reported in Northern Nigeria waters was 1 meter and 6kg, respectively (Offem et al., 2008, Reed et al., 1967. In Northern Nigeria, the fish had prevalence during the months of July and August each year (rainy season), with rising river level (Ekwu, 2008). Heterotis niloticus has become popular in fish farming in Nigeria today due to its fast growth rate, ability to withstand stress, ability to survive in water with low oxygen content, which has endeared it to many fish farmers (Akegbejo-Samsons et al, 2004;Adite et al., 2006).

AIM AND OBJECTIVES
In this study, the abundance, condition factor, fecundity and gonadosomatic index were investigated to estimate the species abundance, wellbeing, and the reproductive capacity indices of the Heterotis niloticus in the Great Kwa River, with the view to encouraging conservation and rational measures for sustainable management of the species. The study also aimed at determining the spawning time of H. niloticus using gonadosomatic index hepatosomatic index and egg size in the Great Kwa River. The decrease in observable stock and the quest to investigate the breeding season of Heterotis niloticus justify this research.

STUDY AREA
The Great Kwa River is a freshwater body which lies between latitude 4 o 45ʹ and 5 0 12ʹN longitude 8 0 20ʹ and 8 0 31ʹE (CRBDA, 1982) is located in a forested belt, and surrounded by Rain forest, freshwater swamp and mangrove swamp. The tidal flow from the Cross River Estuary, occasionally increases the salinity and permits some aquatic organisms from the estuary to flow to the river with tidal movement. Three sampling station were chosen; Station-1: Obufa Esuk , Station-2: Esuk Otu and Station-3: Eusk Atimbo to cover the entire river for collection of landings from local artisanal fishers. The collection stations are indicated in figure 1. Sampling was done forth nightly from January to December to cover all the seasons of the year.

LABORATORY ANALYSIS
The fish were preserved in a plastic trough loaded with ice block and was transported to Fisheries and Aquaculture Laboratory in the University of Calabar, Calabar for analysis. The total length (TL) to the nearest 0.1cm was taken on the measuring board and weight of each of the fish to the nearest 0.1g was measured using a METLAR MT-5000D electronic balance. Each fish was cut opened at the visceral region with a pair of scissors and the single gonad which is situated at the left side of the fish was removed and gonad weight was measured to the nearest gram. The fish liver was removed and measured to the nearest gram. Gender was determined by macroscopic examination of gonads according to Moreau (1982).
Fecundity estimation: Fecundity was estimated from direct and total counts of eggs in the ovaries of fish in the most advanced state of development (Njiru, et al., 2006). Each weighed ovary was cut into sub-samples of 1g.
The sub-samples were derived from three sections of the ovary viz: anterior, middle and posterior portions. They were preserved in the modified Gilson fluid inside small glass bottles and shaken periodically to loosen the oocytes, this fluid helps to harden the eggs for counting and diameter measurement. Ovaries of each fish were preserved for a maximum of 5 days before counting the eggs to determine the fecundity (Ekanem et al., 2004).
The eggs were rinsed and dewatered using 333 µm square mesh screen and low vacuum suction to remove the resulting disintegrated ovarian tissues. The eggs were then dispersed into Petri dishes and any large clumps were gently separated. Counting was done using a stereomicroscope. The eggs per each gram sub-samples were counted. The average for the three sub-samples (anterior, middle, and posterior parts of ovary) was taken as the number of eggs per gram weight of ovary. Therefore, fecundity was calculated by multiplying the total weight of ovary by the number of eggs per gram weight of ovary (Ekanem et al., 2004). The relationship between fecundity and body weight (Wt), fecundity and total length (TL), fecundity and ovary weight. fecundity and Gonadosomatic index (GSI) were estimated using the regression analysis.
The relationship between fecundity (F) and total length (L) and body weight (W) was represented by the relationship: (1) respectively, where F represents fecundity, 'a' is constant, 'b' represents the regression co-efficient, while L and W represent total length and body weight respectively.
Scatter diagrams of fecundity against total length, body weight, GSI of the fish were drawn. Egg diameter was measured using calibrated light microscope. Regression lines were fitted on the scatter diagrams by the least square method (Draper and Smith, 1966). A linear regression analysis by means of logarithm transformation was used to study the relationship between fecundity (F) and other variables. Where K = Condition factor, W = Weight of fish, L = Length of fish (cm) and 100 is a constant. (Richter, 2000).  (table 2.) the female was relatively more than the male but there was no significant difference (p>0.005). One single gonad (ovary) was seen on the left part of the female fish when dissected       (Adite, et al., 2006;Lopez-Fernander et al., 2003;Dankwa et al., 1999). Heterotis niloticus were in better condition in the months of January, February, March, September, October and December, this is probably due to better feeding regime which resulted from availability of food materials at the onset and after the rainy season. Better condition was recorded in the males than in the females which may probably be due to the fact that males have better foraging ability and conservation of stored food energy than females. This is comparable to the report of Mgbenka and Eyo (1992) on Clarias gariepinus in Anambra River Basin, Nigeria.

Gonadosomatic index (GSI
The peak mean value of GSI was recorded in January and May with minor peak in July to August reflecting the spawning seasons. H. niloticus is observed to spawn throughout the year especially during the rainy season this is similar to the finding of Adite et al., (2006). Hepatosomatic index did not show a definite pattern during this study rather showed an inverse relationship with gonadosomatic index (GSI) during the spawning period of this species.
This explains the requirement of energy demanded from body organs such as the liver during gonad development, as reported by Ekanem et al., (2004). The highest egg diameter (0.92±0.01) was recorded in May which has coincided with the performance of GSI, to confirm spawning period.
The fecundity regression statistics indicated variability tendencies about functional relationships between fecundity and length, fecundity and total weight, the same was also observed between fecundity and ovary weight, fecundity and gonadosoatic index. The correlation coefficient (r) for regression of the above-mentioned variables were significantly different at (P<0.05). The linear relationship is represented in figures 3 to 7. The differences that was established between fecundity and length, weight, gonadosomatic index and ovary weight could be due to feeing, environmental condition, season, type of food materials available, spawning period (Fawole and Arawomo, 2000;Ekanem, et al., 2004 andOlele, 2010). The fecundity of H. niloticus (African Bonytongue) in generally could be said to be low when compared to other fish species such as Terapon jarbua with 115,920 eggs (Nandikeswari et al., 2014), Pseudotolithus elongates with 808,911 eggs, (Ekanem et al., 2004), C.striata with 79,436 eggs (Duong et al., 1997), Pomadasys commsersonni with fecundity range of 214,510 -1,421,520 eggs, P. jubelini 37,926 eggs and C. gariepinus fecundity range of 15,667-650,625 eggs for fish size range of 39.5-82.5cm length (Abayomi and Arowomo 1996).
An inverse relationship between the gonadosomatic index and hepatosomatic index was displayed in January, May, July and August indicated high reproductive activity and low energy in the liver. This also showed that H.
niloticus is all year round spawner. Sex ratio of 1:1 was maintained in the river during the study period.

CONCLUSION
Great Kwa River present a favourable environmental condition for H. niloticus, with a good mean condition factor suggesting that food was easily available for the fish. The fish was found to be asynchronous breeder with the ability to spawn all year round. There is a log linear relationship between fecundity and weight, length, ovary weight and gonadosomatic index in H. niloticus Proper management of the natural water bodies to avoid menace of industrial effluents, oil pollution and destruction of vegetation necessary to ensure better habitat condition for the fish and breeding activities is solicited.