An Eco-biological Study of the Mosquitofish, Gambusia affinis, from the Eastern Province of Saudi Arabia

An effort was made in order to know mosquitofish, Gambusia affinis habitat and eco-biology by studying the water quality, length-weight relationship, sex ratio and feeding in different seasons and locations. Sampling was done at Al-Hassa and Al-Qateef drainage canals in the eastern province of Saudi Arabia during summer and winter seasons to record physico-chemical data of the waters and to collect the freshwater mosquitofish. Mosquitofish were found to be well adapted to some extreme conditions of the area: such as high turbidity, high salinity (up to 17.34 ppt), high ammonia (up to 7.5 ppm), low oxygen (down to 1.3 ppm) at Al-Hassa, and shallow water (down to 10cm), waste water contaminated with oil droplets or diary by-products, and, hard water (up to 3420 ppm) at Al-Qateef area. The regressions of log-transformed data were used to test the growth. It was observed that growth in weight is almost proportional (isometric) to the cube of its length and the relationship between total length and total weight for both sexes was curvilinear and statistically significant. The regression equations (W = aLb) for mosquitofish were calculated and the values of b for male and female fish from Al-Hassa were found to be 3.18 and 3.26 for, respectively in the summer and 3.14 and 3.13, respectively in the winter. Values of b for male and female mosquitofish from Al-Qateef were calculated to be 2.86 and 3.05, respectively in the summer and 3.29 and 3.38, respectively in the winter. Value of the slope in all the regression equations was little higher than (3) that coincide with the slope of an ideal fish growth. Sex ratio of mosquitofish showed higher percentage of females at both Al-Hassa and Al-Qateef. Analysis of variance among R2 values revealed no significance differences (P 0.05) in the growth between Al-Hassa and Al-Qatif populations. Green algae dominated among the ingested food items followed by the mosquito larvae, benthic algae, other insects and crustaceans. Consequently, the fact that mosquito larvae were the second most dominant food items in Gambusia food together with their ability to survive extreme conditions of the area indicates the significance of mosquitofish in controlling the mosquitoes in Saudi Arabia.