Water quality and fish species composition inside and outside the Cai Khe floodgate in Can Tho city

Abstract

Assessment of water quality and study on fish species composition were conducted for 4 months from March and June 2024 at the Cai Khe Floodgate. The water samples were measured directly at the Cai Khe Floodgate by using advanced equipment. The fish samples were collected directly and indirectly through fishermen by different kinds of fishing gear such as gill nets, fishing rods, push nets, and trawls. From late April to early May, pH levels and temperatures in the study area peaked, ranging from 7.1 to 7.8 and 30.6 to 32.2 ℃, respectively. Dissolved oxygen remained stable, with levels between 3.7 and 5.06 mg/L, while tide depths varied from 1.6m to 5.0m, and water transparency ranged from 25 to 71cm, with lower values observed in March and higher values during the rainy season in late May and June. The result showed that 43 species belonging to 18 families and 5 orders were identified. The most abundant order containing 14 species (33%) was Perciformes, followed by Cypriniformes and Siluriformes with 13 species (30%) and 11 species (26%). In addition, Clupeiformes consisted of 4 species, accounting for 9% of the total, while Characiformes only had 1 species, making up 2% of the total. A total of 39 species were recorded in the outside floodgate (91.7%), while 25 species were identified in the inside floodgate (58.1%). The results also indicated that catch per unit effort (CPUE) was relatively low and fluctuated through the sampling sites and times. The CPUE data indicates that fishing methods with push nets peaked at 2.94 kg/h and trawls at 4.62 kg/h in June. Inside the area, CPUE for push nets fluctuates between 1.62 kg/h and 2.87 kg/h, while hook and line range from 0.65 kg/h to 1.48 kg/h. Gill nets have the lowest CPUE outside, ranging from 0.17 kg/m/h to 0.42 kg/m/h across the months.