Experiments
Two experiments were conducted to estimate the importance of density and the shelter for
the fish. The first experiment focused on the effect of stocking density on growth and
survival. The second experiment focused on the effect of shelter on growth and survival.
The first experiment was conducted for a period of 8 weeks from June to July, 2011.
The cages were installed at 20 cm above the tank bottom to allow sufficient flow of water
underneath the cage. Three treatments differing in stocking densities were employed with 3
replicates each. Stocking densities were 50 , 250 and 500 fish/m2. The marble goby juveniles
were fed with living food organisms such as Moina sp. and Chironomus sp. larvae. During the
experimental period fish were hand-fed to satiation twice a day at 08.00 and 17.00 h,
respectively.
The second experiment was conducted for a period of 8 weeks from August to
September, 2011. The cages were prepared as mentioned earlier. Two treatments were
carried out and one treatment consisted of a shelter and the other without shelter (control).
The experiment was conducted with 3 replicates per treatment. The shelter was made of
black plastic corrugated pipe for car which was cut in half (70 mm external diameter). The
tube had both internal and external grooves, creating a 33.0 cm length shelter with 12
grooves on both sides (Figure 1). The shelter had a screw at the start and the end of tube for
weighing.
Figure 1. Shelter made of car corrugated pipe. (A) Overall view of the shelter. (B) Lateral
view showing height, the groove width and height of one groove.