Lesser spiny eel (Macrognathus aculeatus) feeding preferences in the Progo River, Yogyakarta, Indonesia

Abstract. Djumanto. 2023. Lesser spiny eel (Macrognathus aculeatus) feeding preferences in the Progo River, Yogyakarta, Indonesia. Intl J Bonorowo Wetlands 13: 36-42. Lesser spiny eel (Macrognathus aculeatus Bloch, 1786) is a highly valued fish species in the Progo River, Yogyakarta, due to its delectable taste, high nutritional value, and attractive aquarium filler. Therefore, this study aims to identify the dietary preferences of M. aculeatus collected between September 2020 and March 2021. Each fish was measured for individual length and weight, followed by an abdomen examination and digestive tract extraction. The intestinal length was also measured, and the digestive tract contents were classified based on the type and volume. Other parameters examined included relative gut length, the proportion of each kind of feed, the index of the largest portion, and the trophic level. The results showed that the ratio of gut length to total length ranged between 0.51 and 0.67, indicating that M. aculeatus were carnivorous. Their diet's six categories of organisms included crustaceans, annelids, insects, phytoplankton, zooplankton, and detritus. Female M. aculeatus was found to primarily consume shrimp (77.88%), followed by additional detritus feed (19.53%) and complementary feed (3%). Meanwhile, the males consumed 99.04% shrimp as their primary diet, and the remaining 0.9% were complementary. The feed niche area for female and male M. aculeatus was 0.137 and 0.005, respectively, indicating a minimal diet selection. Based on the results, the larger the fish, the more limited the feed options available. That indicates domestication and reintroduction should be made to preserve genetic diversity through food formulation and spawning from natural stocks.