Effects of flow velocity on growth and physiology of juvenile largemouth bass ( Micropterus salmoides ) in recirculating aquaculture systems

Abstract

The cultivation of largemouth bass (Micropterus salmoides) in recirculating aquaculture systems (RAS) has become a growing trend. To ensure the welfare of juvenile largemouth bass in RAS, the effects of different flow velocities on their growth and physiology were explored, considering the flow velocity in real production. Following the stable water quality, juvenile largemouth bass with a body mass of 1.92 ± 0.38 g and body length of 4.50 ± 0.36 cm were reared at three different flow velocities of high flow (HF, 18 cm/s, 4.00 bl/s), middle flow (11 cm/s, 2.45 bl/s, actual average flow velocity of aquaculture) and low flow (4 cm/s, 0.90 bl/s) respectively. The whole experiment lasted 66 days. Results showed that different flow velocities had significant effects on the growth, digestive enzyme activities, antioxidant capabilities and immune capabilities of juvenile largemouth bass. HF can significantly increase the cumulative food intake, hepatosomatic index, weight gain rate, specific growth rate and condition factor of largemouth bass juveniles (p < 0.05). Flow velocity had no significant effect on feed conversion rate (p > 0.05), but the mean of feed conversion rate in HF group was the lowest. Under the HF condition, the activities of trypsin and amylase increased significantly (p < 0.05). For lipase activity, although no significant differences were observed between groups (p > 0.05), the mean of lipase activity increased as the flow velocity increased. With regard to the antioxidant and immune capacity, the malondialdehyde content in HF group significantly decreased (p < 0.05), and the immunoglobulin M content significantly increased (p < 0.05). From the above, following the HF velocity condition, fish growth, oxidative defence, immune capacity and digestive capacity could be improved to a large extent. To achieve higher growth, it is recommended circulating flow velocity of no less than 18 cm/s in largemouth bass at the juvenile stage (approximately 1.9-37.5 g and 4.5-14.5 cm long).

Environmental enrichment in fish aquaculture: A review of fundamental and practical aspects

“…Shi et al 232 demonstrated that sustained swimming training have direct effects on filet texture of European seabass. Moreover, different flow velocities had significant effects on the growth, digestive enzyme activities, antioxidant capabilities, and immune capabilities of juvenile largemouth bass ( Micropterus salmoides ) in recirculating systems (RAS) 233 . A study on Nile tilapia showed that water flow can help the fish to cope better with stressful events, such as being introduced into novel environments 234 .…”

“…Moreover, different flow velocities had significant effects on the growth, digestive enzyme activities, antioxidant capabilities, and immune capabilities of juvenile largemouth bass (Micropterus salmoides) in recirculating systems (RAS). 233 A study on Nile tilapia showed that water flow can help the fish to cope better with stressful events, such as being introduced into novel environments. 234 In addition, optimal exercise may also have beneficial effects on reproduction control.…”

Effects of flow velocity on water quality and ammonia excretion in recirculating aquaculture system culturing juvenile largemouth bass (Micropterus salmoides)

“…In this experiment, the total volume of water in the RAS was 110 L and a 25 L reservoir was used instead of a biofilter. Theory predicted maximum ammonia concentration was about 3.6 mg/L, which was in the safe range [24] .…”

“…Kvamme et al [34] found that the ammonia discharge rate of Atlantic salmon decreased with an increasing flow rate in the range of 0.2-0.5 L/(kg•min). Chen et al [24] found that the digestive enzyme activity of juvenile largemouth bass was enhanced as the flow velocity increased, which may also lead to enhanced protein uptake and reduced ammonia nitrogen excretion. To date, there is no general consensus as to the effects of flow velocity on the swimming and metabolism of fish species.…”

A review of influencing factors on a recirculating aquaculture system: Environmental conditions, feeding strategies, and disinfection methods

“…Furthermore, a higher water velocity can make more particles suspend in the water, which is conducive to the filtration and removal of suspended particles. So, increasing the water velocity in the peak of ammonia discharge can contribute to the ammonia degradation and water purification (Chen, 2021). Therefore, it is beneficial to provide an appropriate water flow rate for the species cultured.…”