Turbidity derived from palm oil mill effluent alters feeding ability of male siamese fighting fish (Betta splendens, Regan 1910)

To date, several harmful effects of Palm Oil Mill Effluent (POME) have been reported on aquatic organisms, including fish. However, the turbidity effects of POME on the feeding ability of fish are still unexplored. We first assessed the turbidity effects of POME on the feeding ability of male siamese fighting fish (Betta splendens). Siamese fighting fish were exposed to < 1 NTU (control) and five concentrations of POME turbidity levels, namely 20 NTU (Treatment A), 40 NTU (Treatment B), 60 NTU (Treatment C), 80 NTU (Treatment D), and 100 NTU (Treatment E). Each of the control and treatment groups was maintained in five replicates. Preference tests were carried out in a 10-L aquarium (35 ×21×25 cm3). The feeding rate, time to capture first prey, aggressive behaviour, foraging area, and retinal light adaptation rate and retina histopathology were analyzed. The exposure time for the determination of feeding rate, foraging area, and retinal light adaptation rate and retina histopathology was set for 15 min, while for aggressive behaviour test, the exposure duration was 5 min. Results showed that the feeding rate, aggressive behaviour and foraging area significantly decreased with increasing turbidity levels of POME. In contrast, the time to capture first prey significantly increased. No significant changes in retinal light adaptation rate was recorded between treatments. Furthermore, results showed several retinal degenerations, including reduced granular spherical cells (GL) and detachment of bipolar cells from photoreceptor cells (DBPC) in siamese fighting fish exposed to high-level turbidity of POME. This study provides valuable information to support POME remediation management, especially turbidity parameters.