Fish diversity in selected small lakes in Mindanao, Philippines

It is said that species richness depends on the size and distance of water bodies and that the larger and closer the lakes are, the more species they have, more than smaller and more distant lakes. Based on the literature, large lakes covering large areas are given more research importance, while the global role of small lakes is less studied. For this reason, this study aimed to determine the relationship between the surface area and fish species diversity of the six isolated lakes found on the island of Mindanao, namely Lakewood, Apo, Napalit, Holon, Tiktikan, and Kanlunes lakes. Five of these lakes are considered open and connected, while Kanlunes Lake is closed and isolated. Results show an acidic pH value of 4.73 in Lakewood. Only Napalit Lake was able to achieve excellent oxygen saturation. A total of 33 families with 59 species were recorded, 46 of which are native to the Philippines, one is endemic, Rasbora everreti, and 11 are known to be introduced. It was observed that the introduced Oreochromis niloticus was common to the five lakes, except for Tiktikan Lake. This lake is the most species-rich and abundant, but showed significant unevenness in its population. Also, results showed that the lake surface area has no significant effect on species diversity and evenness. Though the value of strength association is insignificant, a directly proportional relationship between surface area, diversity, and evenness can be observed. It should also be noted that the actual relationship between taxon diversity and lake size differs widely among species. But it should also be stressed that the existing relationship between taxon diversity and lake size might vary widely among species. The diversity observed among the six lakes could also be attributed to many other ecological factors, including the anthropogenic factor, and should be further studied.