Gut Content Analysis of Selected Commercially Important Species of Coral Reef Fish in the Southwest Part of Iligan Bay, Northern Mindanao, Phillippines

The diet composition of selected economically important reef fishes was described. Sampling for fish and plankton was done every month from July to December 2004 in eight sampling stations located in Maigo and Kauswagan, lanao del Norte. Nine fish species were selected for the gut content study. The nine species belong to seven families: the Gerreidae (Gerres oyena), Leiognathidae (Leiognathus splendens), Lethrinidae (Lethrinus insulindicus), Scaridae (Scarus bowersi), Siganidae (Siganus guttatus and Siganus vermiculatus), Theraponidae (Therapon jarbua and Therapon sp.) and Mullidae (Upeneus caeruleus). The result of the stomach or gut content analysis showed that majority of the fish species preyed on zooplankton and benthic animals. These fishes were categorized as generalist species based on Costello's method. They are represented by Gerres oyena, Leiognathaus splendens, Lethrinus insulindicus, Therapon jarbua, Therapon sp. and Upeneus caeruleus except for fishes belonging to Family Scaridae (Scarus bowersi) and Family Siganidae (Siganus guttatus and Siganus vermiculatus) which exclusively fed on algae and were categorized as strict herbivores. A total of 46 zooplankton groups were identified and 76.51% of the total population was composed of copepods which included calanoida, cyclopoida, harpacticoida, copepod nauplius and eggs. Comparison between the abundance of zooplankton between stations in Maigo, and Kauswagan, Lanao del Norte showed no significant difference (p > 0.05) in both areas. This study showed that out of the nine economically important reef fishes, six fish species preferred to prey on zooplankton species. This further showed that despite the abundance of zooplankton in the environment, planktivorous fishes preferred to prey on some zooplankton groups like copepods, amphipods and crab megalopa. Hence, zooplankton as prey of selected economically important reef fishes should be conserved and harvesting of commercial fishes should be controlled