Effects of substrate roughening on the swimming performance of Schizothorax wangchiachii (Fang, 1936) in the Heishui River: Implications for vertical slot fishway design

Re-establishing the natural connectivity of rivers using fishways may mitigate the unfavourable effects of dam construction on riverine biodiversity and freshwater fish populations. Knowledge of the swimming performance of target species in specific regions is critical for designing fishways with a high passage efficiency. Substrate roughening with river stones of fishways is considered to improve fish swimming capacity by benefiting from reduced-velocity zones with lower energetic costs. However, the effectiveness of rough substrates in energy metabolism is rarely tested. We investigated the effect of substrate roughening on the swimming capacity, oxygen consumption and behaviour of Schizothorax wangchiachii from the Heishui River in a flume-type swimming respirometer. The results showed that substrate roughening improved critical and burst swimming speed by ~12.9% and ~15.0%, respectively, compared to the smooth substrate. Our results demonstrate that increased reduced-velocity zones, lowered metabolic rate and tail-beat frequency support our hypothesis that lower energetic costs improve fish swimming performance in rough substrate compared to smooth treatment. The traversable flow velocity model predicted that maximum traversable flow velocity and maximum ascent distance were higher over rough compared to smooth substrate fishways. Fishway substrate roughening may be a practical approach to improve fish swimming upstream for demersal riverine fish.

Deterministic processes dominate microbial community assembly in artificially bred Schizothorax wangchiachii juveniles after being released into wild

Fish artificial breeding and release is an important method to restore wild populations of endemic fish species around the world. Schizothorax wangchiachii (SW) is an endemic fish in the upper Yangtze River and is one of the most important species for the artificial breeding and release program implemented in the Yalong River drainage system in China. It is unclear how artificially bred SW adapts to the changeable wild environment post-release, after being in a controlled and very different artificial environment. Thus, the gut samples were collected and analyzed for food composition and microbial 16S rRNA in artificially bred SW juveniles at day 0 (before release), 5, 10, 15, 20, 25, and 30 after release to the lower reaches of the Yalong River. The results indicated that SW began to ingest periphytic algae from the natural habitat before day 5, and this feeding habit is gradually stabilized at day 15. Prior to release, Fusobacteria are the dominant bacteria in the gut microbiota of SW, while Proteobacteria and Cyanobacteria generally are the dominant bacteria after release. The results of microbial assembly mechanisms illustrated that deterministic processes played a more prominent role than stochastic processes in the gut microbial community of artificially bred SW juveniles after releasing into the wild. Overall, the present study integrates the macroscopic and microscopic methods to provide an insight into the food and gut microbial reorganization in the released SW. This study will be an important research direction to explore the ecological adaptability of artificially bred fish after releasing into the wild.

Improved aerobic and anaerobic swimming performance after exercise training and detraining in Schizothorax wangchiachii: Implications for fisheries releases

Swimming performance (aerobic and anaerobic) is often used to predict the ability of fish to adapt and survive. Fish raised in captivity are typically poor swimmers and have lower survival rates than wild conspecifics when released into the natural environment. We investigated the potential for exercise training to enhance the swimming performance of Schizothorax wangchiachii held in captivity. Juvenile fish (mean body mass 1.40 ± 0.13 g, mean body length 4.36 ± 0.24 cm) were trained under five different regimes [3 cm·s^-1 control group (C), 10 cm·s^-1 for 6 (L6) and 12 h (L12) per day and 20 cm·s^-1 for 6 (H6) and 12 h (H12) per day] for 30 days and then detrained for 20 days (i.e. no training). Aerobic (i.e. critical swimming speed, U_crit), anaerobic swimming performance (i.e. endurance time at 1.2 or 1.5 U_crit), and morphological parameters were measured at the beginning (T₀), after 30 days of exercise training (T₃₀) and after 20 days of detraining (DT₂₀). Aerobic exercise training significantly improved the U_crit, endurance time at 1.2 and 1.5 U_crit of juvenile S. wangchiachii (P < .05). After 20 days of detraining, both the aerobic and anaerobic swimming performance of the H6 and H12 groups declined and no longer differed from the control group indicating a failure to maintain improved swimming performance, whereas improved swimming performance was maintained in L6 and L12 groups. No significant difference in swimming performance was found between 6 and 12 hours training at 10 cm·s^-1. Thus, exercise at close to 10 cm·s^-1 for 6 h per day for 30 days or a longer time periods prior to release appears to be a suitable regime for swimming performance enhancement, potentially increasing survivability of released S. wangchiachii in wild.

Effects of cyclical short-term food deprivation and refeeding on compensatory growth and gene expression of SOD, GPX and HSP70 in Schizothorax wangchiachii

The present study evaluated the effects of cyclical short-term food deprivation and refeeding on growth performance, body composition, and gene expression of SOD, GPX and HSP70 in Schizothorax wangchiachii.The experimental design included four feeding protocols for eight weeks: feeding every day of the week (control), starvation for one day and refeeding for six days per week (S1F6 treatment), starvation for two days and refeeding for five days per week (S2F5 treatment), and starvation for three days and refeeding for four days per week (S3F4 treatment). The results showed that no significant difference in final body weight, specific growth rate and feed conversion efficiency were observed among the treatments (P > 0.05).The feeding rate significantly increased with the duration of food deprivation per week compared to the control (P < 0.05). The expression levels of HSP70 showed no significant differences in the gill, liver and spleen of S.wangchiachii subjected to different feed restriction regimes(P > 0.05), but in the kidney, the expression levels of HSP70 were significantly downregulated in S1F6 and S2F5 compared to the control(P < 0.05). The expression levels of SOD and GPX in the examined tissues were not affected by the different feed restriction regimes(P > 0.05). In conclusion, full compensatory growth was observed in S.wangchiachii under eight cycles of food deprivation and refeeding. Hyperphagia was the main mechanism of compensatory growth of S.wangchiachii.