Elevated CO2 and food ration affect growth but not the size-based hierarchy of a reef fish

Multifaceted Nothobranchius

Annual killifish of the genus Nothobranchius are seeing a rapid increase in scientific interest over the years. A variety of aspects surrounding the egg-laying Cyprinodontiformes is being extensively studied, including their aging. Inhabiting drying water bodies of Africa rarely allows survival through more than one rainy season for the Nothobranchius populations. Therefore, there is no lifespan-related bias in natural selection, which has ultimately led to the decreased efficiency of DNA repair system. Aging of the Nothobranchius species is studied both under normal conditions and under the influence of potential geroprotectors, as well as genetic modifications. Most biogerontological studies are conducted using the species Nothobranchius furzeri (GRZ isolate), which has a lifespan of 3 to 7 months. However, the list of model species of Nothobranchius is considerably wider, and the range of advanced research areas with their participation extends far beyond gerontology. This review summarizes the most interesting and promising topics developing in the studies of the fish of Nothobranchius genus. Both classical studies related to lifespan control and rather new ones are discussed, including mechanisms of diapause, challenges of systematics and phylogeny, evolution of sex determination mechanisms, changes in chromosome count, occurrence of multiple repeated DNA sequences in the genome, cognitive and behavioral features and social stratification, as well as methodological difficulties in working with Nothobranchius.

Effects of exposure to elevated temperature and different food levels on the escape response and metabolism of early life stages of white seabream, Diplodus sargus

Recent literature suggests that anthropogenic stressors can disrupt ecologically relevant behaviours in fish, such as the ability to escape from predators. Disruption of these behaviours at critical life history transitions, such as the transition from the pelagic environment to the juvenile/adult habitat, may have even greater repercussions. The literature suggests that an increase in temperature can affect fish escape response, as well as metabolism; however, few studies have focused on the acute sensitivity responses and the potential for acclimation through developmental plasticity. Here, we aimed at evaluating the acute and long-term effects of exposure to warming conditions on the escape response and routine metabolic rate (RMR) of early life stages of the white seabream, Diplodus sargus. Additionally, as food availability may modulate the response to warming, we further tested the effects of long-term exposure to high temperature and food shortage, as individual and interacting drivers, on escape response and RMR. Temperature treatments were adjusted to ambient temperature (19°C) and a high temperature (22°C). Feeding treatments were established as high ration and low ration (50% of high ration). Escape response and RMR were measured after the high temperature was reached (acute exposure) and after 4 weeks (prolonged exposure). Acute warming had a significant effect on escape response and generated an upward trend in RMR. In the long term, however, there seems to be an acclimation of the escape response and RMR. Food shortage, interacting with high temperature, led to an increase in latency response and a significant reduction in RMR. The current study provides relevant experimental data on fishes' behavioural and physiological responses to the combined effects of multiple stressors. This knowledge can be incorporated in recruitment models, thereby contributing to fine-tuning of models required for fisheries management and species conservation.

Increasing temperature and prey availability affect the growth and swimming kinematics of Atlantic herring (Clupea harengus) larvae

Climate change will increase the magnitude and duration of warming events and the variability in the phenology and abundance of available prey to the early life stages of fish. These factors influence physiological, behavioral and ecological processes, impacting growth, development and survival. Using a fully factorial design with two prey-availability treatments (1200 prey items L^-1 (high prey abundance) or 40 prey items L^-1 (low prey abundance)) under three temperature regimes (8, 10 and 12°C), the swimming kinematics of 6-week old spring-spawning Atlantic herring larvae were examined using silhouette video photography. Higher temperatures combined with food limitation significantly decreased the growth and swimming kinematics of larval herring, with the most negative effect observed in larvae reared at 12°C and exposed to low food abundances. Specifically, larvae displayed reduced locomotory behaviors and reduced vertical movements. By contrast, larvae reared at high prey abundance and at 12°C displayed more active swimming and exploratory behavior, as evidenced by an increase in both locomotory behavior and vertical and horizontal turn angles, suggesting increased motivation to search for food. This research highlights the importance of determining to what degree fish larvae are sensitive to changes in temperature and how these changes might be further influenced by food availability.