Najda Athman Bacha, Cosmas Munga, David Mirera
Abstract:
Siganus sutor commonly known as the shoemaker spinefoot rabbitfish is among the prevalent captured fish species in the small scale fishery and one of the most commercially important demersal fisheries resources along the Kenya coast. Studies indicate that the stock status of S. sutor is way below its sustainable limit due to overexploitation. One way of improving the dwindling stock of this species is mariculture production. This study therefore assessed the growth performance of S.sutor under experimental feeding in plastic water tanks. Specimens of juvenile S. sutor were collected from the wild, acclimatized and fed on formulated feed from natural occurring macroalgae and compared with fishmeal and a mixture of fish meal and macroalgae feed. The three formulated feed types were: treatment I contained 100% macroalgae, treatment II contained 0% macroalgae (fishmeal) and treatment III contained 50% macroalgae (mixture of macroalgae and fishmeal). Fish specimens were stocked in different flow-through systems of 1000-liter plastic tanks using a 3 by 3 factorial design with aeration at a stocking density of 20 individuals/m3 and experimental feeding was conducted. Initial measurements (total length, cm and individual weight, g) of fingerlings were recorded using a graduated fish measuring board and electronic weighing balance, respectively. Growth monitoring of specimens in the tanks was done bi-weekly for 28 days. The overall mean weight and total length of fish specimens under experimental feeding were calculated for all treatments. Fish specimens fed with fishmeal recorded the highest overall mean weight across all treatments, accounting for 32 ± 7.07 g followed by macroalgae and mixed feeds accounting for 23.34g± 0.83 and 22.80g ± 0.75, respectively. Specimen fed with Macroalgae diet (T1R1) recorded the highest total weight gain at 25.6g followed by mixed diet (T3R1) and fishmeal diet (T2R2) with 19.8g and 17.2 g, respectively. Fish fed with a mixed diet (both fishmeal and algae) recorded the fastest growth in terms of total length gained by 0.41 cm, followed by macroalgae diet with 0.23cm whereas fish fed with a fishmeal diet had a decrease in mean length by 0.05 cm. The highest survival rate was recorded in fish fed with macroalgae diet at 83.0%, followed by those fed with mixed diet and fishmeal at 81.3% and 69.3%, respectively.Regarding the feed conversion ratio, the algae diet was proficiently utilized more with food conversion ratio of 1.59. Fish specimensin experimental treatments II (fishmeal diet) and III (mixed diet) were not in good condition with condition factor (K) at -19.78 and -29.92, respectively. Based on these results, it is evident that the use of the macroalgae diet offers promising returns in terms of S. sutor survival rate compared to the fishmeal diet although with higher growth performance.