Growth, survivorship, and predator avoidance capability of larval shortnose sturgeon (Acipenser brevirostrum) in response to delayed feeding

Embryological incubation temperature modulates behaviour in larval white sturgeon (Acispencer transmontanus)

White sturgeon inhabit large rivers and estuaries along the Pacific coast of North America and play important ecological and cultural roles. As with other poikilotherms, the expected rise in global temperatures will create physiological challenges for sturgeon, including direct effects on physiological rates, and may also cause changes in behaviour that impact survival. In this study, we investigated 'carryover effects' in white sturgeon (Acipenser transmontanus) by incubating fish at one of three embryological temperatures (12 °C, 15 °C, or 18 °C) from fertilization to hatch, and then holding them at 15 °C for the following 30 days post-hatch (dph). We investigated the effect of these incubation temperatures on subsequent behaviours, including locomotion and anxiety-like behaviour, at 18, 24 and 30 dph. The open field test was used to quantify distance moved by the fish and time spent near the outer wall of the arena (to quantify thigmotaxis, an indicator of anxiety-like behaviour) and recorded with motion-tracking software. This test was also used to compare behaviour during the day versus night (at 21 dph) and hourly at night (at 28 dph). Additionally, a light/dark test commonly used in rodents and other fish species was performed for the first time on larval sturgeon at 24 dph. We found a significant family effect; the impact of embryo rearing temperature on locomotion and thigmotaxis varied depending on the family lineage of the fish. Furthermore, we provide evidence that larval sturgeon exhibit greater locomotion at 24 and 30 dph compared to 18 dph, and have a preference for the light zone of the light/dark test. Our findings identify a more nuanced effect of incubation temperature on later life stages that varies with family lineage and underscores the need to consider such variation in research and conservation programs.

Too Hot to Handle: A Meta-Analytical Review of the Thermal Tolerance and Adaptive Capacity of North American Sturgeon

Understanding how ectotherms may fare with rising global temperatures and more frequent heatwaves is especially concerning for species already considered at-risk, such as long-lived, late-maturing sturgeon. There have been concerted efforts to collect data on the movement behavior and thermal physiology of North American sturgeon to enhance conservation efforts; thus, we sought to synthesize these data to understand how sturgeon respond to thermal stress and what capacity they have to acclimate and adapt to warming. Here, we combined a systematic literature review and meta-analysis, integrating field-based observations (distribution and spawning) and laboratory-based experiments (survival, activity, growth, metabolism, and upper thermal limits) for large-scale insights to understand the vulnerability of North American sturgeon to rising global temperatures. We summarized the preferred thermal habitat and thermal limits of sturgeon in their natural environment and using meta-analytical techniques, quantified the effect of prolonged temperature change on sturgeon whole-animal physiology and acute upper thermal limits. While acclimation did not have significant effects on physiological rates or survival overall, there were positive trends of activity and metabolism in young-of-the-year sturgeons, likely offset by negative trends of survival in early life. Notably, North American sturgeon have a greater capacity for thermal tolerance plasticity than other fishes, increasing upper thermal limits by 0.56°C per 1°C change in acclimation temperature. But with limited laboratory-based studies, more research is needed to understand if this is a sturgeon trait, or perhaps that of basal fishes in general. Importantly, with these data gaps, the fate of sturgeon remains uncertain as climate change intensifies, and physiological impacts across life stages likely limit ecological success.

Early nutritional programming in sterlet sturgeon (Acipenser ruthenus) with dietary soybean meal: Assessment of growth performance, body composition, and expression of GH, IGF-I, and Ghrelin genes

This study was performed to assess the impacts of introducing diets containing different levels of soybean meal (SBM) to sterlet sturgeon (Acipenser ruthenus) larvae on growth performance, body composition, and molecular responses in the juvenile stage. The sterlet larvae (57.68 ± 0.66 mg) were weaned onto the formulated diets as follows: a control diet containing 60% fishmeal (FM), and three experimental diets with replacement levels of 15% (SBM15), 30% (SBM30), and 45% (SBM45) of FM with SBM. Then, a total of 260 fish (initial weight: 323.33 ± 11.76 mg) were fed the four different diets for 28 days in triplicates (phase 1, nutritional programming, NP). All treatments were then fed with the FM diet in phase 2 (common phase), and in phase 3 (challenge phase), all experimental groups (6.14 ± 0.08 g) were transitioned to SBM45 for 28 days. At the end of phases 1 and 2, growth performance showed no significant differences among the groups (P > 0.05), while significantly improved in SBM45 than the control at the end of phase 3 (P < 0.05). No significant differences were found among the groups in any phases for whole body composition (P > 0.05). Additionally, the total saturated fatty acids were significantly higher in SBM-based diets than FM at the end of phase 3 (P < 0.05). The mRNA of GH, IGF-I was significantly affected by variation of FM replacement level (P < 0.05). The expression level of Ghrelin was up-regulated in fish fed SBM at the end of phase 3 (P < 0.05). Our findings revealed that NP can positively enhance the adaptation of juvenile sterlet sturgeon to 45% SBM when exposed to the same diets at the larval stage. Further research is being carried out to provide valuable insights into the underlying mechanisms of digestive performance for this species.

The Effect of Different Feeding Applications on the Swimming Behaviour of Siberian Sturgeon: A Method for Improving Restocking Programmes

Restocking programmes of different fish species have been implemented worldwide. However, the survival of hatchery-reared fish after release to riverine ecosystems is at a very low level. One of the reasons for the high mortality rate of post-released fish is their modified swimming behaviour due to the hatchery rearing practice. To investigate one of the possible causes for modified swimming behaviour, Acipenser baerii larvae were exposed to surface- and bottom-feeding applications with day and night light regimes in a factorial design. We also analysed the effect of 5 and 10 days of starvation after different feeding applications on sturgeon swimming behaviour. The surface-feeding application was previously expected to promote the frequent Siberian sturgeon swim up to the mid- and top-water layers in our rearing facilities. However, our results indicated that the modified behaviour of the Siberian sturgeon in our study was caused by fish starvation and a possible predator-free environment rather than by the method of feed application or the day/night light regimes. These results may be used to improve the implementation of restocking programmes either through modified hatchery rearing practice or the training of foraging skills with predator stimuli.