Reproductive Impairment of Tilapia zillii ( Gerv . ) Living in Different Basins of Lake Mariut , Alexandria

This study aimed at inspecting pollution impact on the reproduction process of Tilapia zillii (Gerv.) living in three main basins of Lake Mariut. Our results revealed that there were two main seasons detected for males and females during a whole year of investigation, namely, non-spawning and spawning seasons. In males, though the two seasons started and ended simultaneously, gonadosomatic index values of males living in the relatively clean area were significantly higher than those of the other two polluted areas. However, no structural alterations could be detected in sections of male gonads from the three basins. All stages of maturation were represented in all gonad sections. In females, gonadosomatic index values of fish living in the relatively clean basin were significantly higher than those of fish living in the other two polluted areas. Females living in the relatively clean area attained two prominent peaks during the spawning season compared to one peak for the other two polluted areas. Spawning season for one of the two polluted areas was one month shorter than the reference area. Histologically, belated and deformed maturation stages as well as ruptured and empty follicles were observed in female gonad sections from the two polluted areas.


INTRODUCTION
Lake Mariut is the smallest lake and the most polluted one among the shallow brackish-water Delta Lakes that used to have high fishery production and that gradually became loaded with polluted discharge from the adjacent urban and industrial settlements. 1The combination of pollutants in the Lake caused many sensitive fish genera to disappear.In addition, the quantity and the quality of the least sensitive species that survived had greatly deteriorated and became of low survival rate due to the absence of dissolved oxygen and the presence of high Bull High Inst Public Health Vol.37 No. 3 [2007]   levels of toxic gases such as ammonia and hydrogen sulphide. 2,3[6][7] These effluents can contain chemicals capable of mimicking endogenous hormones, and hence have the potential to disrupt endocrine-mediated processes such as reproduction. 80][11] In mature females of zebrafish, the synthetic estrogen 17a-ethynylestradiol (EE2), detected in sewage effluents and in surface waters, 12,13 was proved to reduce yolk-filled occytes. 14erefore, the aim of the present work was

Sampling Site:
Lake Mariut is an important fishing Lake at the southern area of Alexandria City, Egypt (Fig. 1).It lies at a longitude of 30°10' E and a latitude of 31°10' N and has no direct connection with the Mediterranean Sea.Lake Mariut is mainly divided into four main basins; these are Lake Proper or the main basin, the Fish Farm, the North-western (N.W.), and Southwestern (S.W.).In this study, three stations were chosen for sampling representing three main basins of Lake Mariut.

Study Species:
Each month, for a whole year, about 30 specimens of Tilapia zillii (Gerv.)were bought alive from various fishermen at each basin and brought to the laboratory in oxygen-packed plastic containers.

Gonadosomatic Index (GSI):
To follow up quantitative gonadal growth of T. zillii males and females during a whole year, GSI of gonads were computed using the following equation of Schaefer and Orange 15 ; GSI = Gonad Weight x 100/ Gutted weight, where both gonad and gutted weight of fish were expressed in grams.

Gonads Histology:
Gonads of males and females of T. zillii specimens collected from the three basins of Lake Mariut were cut free and excised into small portions.These portions were fixed in Carnoy's Solution for 24 h, then transferred to 70% alcohol and processed using routine histological techniques.

Statistical Analyses:
Data were expressed as mean ± S.D.
Student t-test was used to compare between the mean values of GSI of the reference area and the heavily polluted areas (t was considered significant at p<0.05).

GSI of Tilapia zillii:
In this study we tried to detect the effect of different types of pollution present in three main basins of Lake Mariut on T. zillii reproduction process through one year of investigation.Our GSI results generally revealed that through a whole year of investigation there were two distinct seasons for all males in all studied areas (Fig. 2).These two seasons are the nonspawning season and the spawning one.In Statistically, the difference was significant (p<0.05).
As for females of T. zillii living in the three studied basins of Lake Mariut, the present study showed that two distinct seasons were distinguishable (Fig. 3).  5][6][7] While many fish genera have disappeared from the Lake, Tilapia zillii was one of those few which had proved to be of higher tolerance and resistance to the surrounding challenges.
Therefore, the present study aimed at testing the reproductive status of T. zillii in response to the severe environmental conditions in which it lives.
Indeed, the present results revealed that though GSI of T. zillii male fish living in relatively clean area and the heavily polluted started and ended both the non-spawning and the spawning in the same months, GSI values recorded in the relatively clean area (especially during the spawning season) were significantly higher than those recorded in the heavily polluted basins.This result agreed with many other investigators who found that there had been a decrease in GSI values reported in adult male trout and carp exposed to estrogens either in water or via food. 16 to detect the reproductive impairment in Tilapia zillii males and females living in three different basins of Lake Mariut, during a whole year of investigation.The approach to this aim mainly based on following up gonadosomatic index (GSI) values of T. zillii males and females throughout the investigation period and by taking sections in gonads of both sexes during two distinct seasons, namely, the non-spawning and spawning seasons.

Fig. 1 :
Fig. 1: Lake Mariut Map showing the three sampling sites: the reference area Babel-Abeed and the two polluted areas Kabbarri and Merghem.
the relatively clean area of BA and the other two polluted areas, non-spawning season extended from October until April with the minimum value recorded in January for BA, in March for Ka and in October for Me.On the other hand, spawning season, in which main spermatogenic activities took place, started in May and ended in September for all males of all studied regions with maximum values recorded in May for males of BA and Ka and in July for Me.However, it was worth noting that during the spawning season, BA area (reference area) exhibited higher values than that of Ka and Me.

Fig. 2 :
Fig. 2: Gonadosomatic index (GSI) of T. zillii males recorded in the three basins during one year; the reference area BA and the two polluted areas Ka and Me.

Fig. 3 :
Fig. 3: Gonadosomatic index (GSI) of T. zillii females recorded in the three basins during one year; the reference area BA and the two polluted areas Ka and Me.
The first station is Babel-