Risk of Expanded Polystyrene Ingestion by Climbing Perch Anabas testudineus

The climbing perch Anabas testudineus is widespread in the inland waters of Vietnam and according to its ecology could have contact with floating plastic waste. Fragments of expanded polystyrene (EPS) are detected in the fresh waters of Vietnam in Khanh Hoa, Lam Dong, and Phu Yen provinces. Our study focused on estimating the probability of ingestion of EPS pellets (size 2.5-3.5 mm) by adult climbing perch. In the experiments, 3 types of treatment pellets were offered to fish: 24 feed pellets (Fps), 24 expanded polystyrene pellets (Pps), and 12 feed and 12 expanded polystyrene pellets (FPps). Fish grasping time of the first pellet was independent in all treatment types. The grasping time of the 12th pellet was insignificant in Fps (63 s) and Pps (75 s). Climbing perch grasped and ingested the 24th Fp significantly (p = 0.02) earlier (143 s), than they grasped the 24th Pp (817 s). Fish with FPp treatment grasped feed along with EPS pellets, but grasping the 12th Fp was significantly (p = 0.02) earlier (49 s) than the 12th Pp (193 s). By the end of the tests, the fish had ingested all feed pellets. We discovered that climbing perch grasped Pps and kept them in the oral cavity, but rejected them in 100% of the cases. This result provided evidence that climbing perch have an effective defense mechanism for avoiding ingestion of expanded polystyrene pellets with a size of 2.5-3.5 mm.