Reproductive Biology of Glossogobius giuris (Hamilton), in Manchar Lake Sindh, Pakistan

Distribution range of Glossogobius giuris (Hamilton) is reported from freshwater and estuaries of Bangladesh, India, Pakistan, and Burma [1]. In Pakistan, the fish is reported in all types of freshwaters in warm areas [2]. This fish is also reported from Chotiari Reservoir [3]. Most of the published worked on biological aspects of G. giuris is from our neighboring countries [4-6]. Previously in Pakistan studies are available on growth and feeding habit of the species [7,8].


Introduction
Gobies are originally marine species, which are still under the process of fresh waterization. Due to their marine origin still many freshwater gobies are observed to tolerate high salinity ranges.
Therefore large numbers of marine gobies are reported to inhabit in freshwaters.
Distribution range of Glossogobius giuris (Hamilton) is reported from freshwater and estuaries of Bangladesh, India, Pakistan, and Burma [1]. In Pakistan, the fish is reported in all types of freshwaters in warm areas [2]. This fish is also reported from Chotiari Reservoir [3]. Most of the published worked on biological aspects of G. giuris is from our neighboring countries [4][5][6]. Previously in Pakistan studies are available on growth and feeding habit of the species [7,8].
Gonadosomatic Index (GSI) is most useful tool in fisheries biology to determine the spawning season of spawning. Knowledge about Gonadosomatic Index and fecundity of any fish is important for understanding its life history, and evaluating the potential of its stock for commercial purposes. Furthermore, such knowledge is also needed for the sound management for the conservation of the Gupta and Shrivastava [9][10][11][12].

Materials and Methods
Fish samples for the current study were collected from Manchar lake over the period of one year from January 2010 to December 2010. The fish samples were carried in ice box to the laboratory, where further observations were made. In the laboratory fishes were sexed, body measurements for total length (TL) were carried out at centimetre scale (0.1 cm) with the help of measurement tap and weighed (g) using scale. Body weight were taken with the help of, later on fishes were gutted to check the gonadal statu/maturation. Egg size was measured during each month, small piece of ovary was removed it was placed on slide, the sketches of eggs were made under Trinocular Microscope (Nikon ECLIPSE E200) and with the help of drawing tube.

Results
A total 335 specimen comprising 159 females and 176 males were examined to determine the reproduction of G. giuris. Percentage of male and female population was 52.53% and 47.46% respectively. The smallest size of mature female was 9.4 cm ( Table 1).
The fish exhibits clear sexual dimorphism, male were with straight, thin and pointed genital papilla while females were with short fleshy and circular genital papilla (Figure 1). Total length of smallest and largest female carrying the mature ovaries recorded 9.4 cm and 24.8 cm, respectively. G. giuris mature females were found with a pair of granular ovaries unequal in length and fully ripen ovaries were orange in color. Based on the smallest size of female with the mature ovaries it can be said that first size of G. giuris at the sexual maturity was 9.4 cm.
Increase in Gonadosomatic Index was observed from February; however it peaked in the month of March and it also remained high from April and June, then after it declined from July to September ( Figure 2). It shows that the fish has prolonged breeding period which persists from March to September in Manchar Lake.
For fecundity analysis total 13 females were used, their total length ranged between 9.4 cm to 24.8 cm. Fecundity of G. giuris ranged from 7346.45 to 39750.45. The average fecundity of G. giuris was 24835.84 ± 10361.74 (Table 2).
Regression analysis between log values of total length and fecundity, gonadal weight and fecundity and total weight and fecundity showed significant relationship. However, fecundity showed comparatively high correlation with total length and gonadal weight, respectively ( Figure 3).
The eggs of G giuris were very small and oval is shape, size ranged between 0.17 to 0.75 (mm) on their longitudinal axis, The average value of egg size was 0.36 ± 0.13 mm (Table 3).

Discussion
Glossogobius giuris exhibited distinct sexual dimorphism, male were found with thin and pointed genital papilla. External sexual dimorphism helps to study the reproductive biology of fishes, and life history traits it also support for determining morphological difference between populations [13]. In total 335 specimens were used to determine the reproduction of G. giuris. The study is based on large number of specimen, percentage of male and female population