Fishes

White croaker (Pennahia argentata) is an ecologically and economically relevant fish species targeted by demersal trawls using diamond-mesh codends at fishing grounds in China, Japan, and Korea. However, the stock has been overexploited, and the capture of undersized individuals is of concern. Further, diamond-mesh codends are known to have varying mesh shape due to the fact that the opening angle in them varies along the codend and during the fishing process. Therefore, to fully understand the effect of mesh size and opening angle on the size selectivity of white croaker, experimental fishing trials and fall-through trials were conducted. By combining the results from these trials, a model was constructed to predict the effect of mesh size and mesh opening angle on size selectivity of white croaker. The predicted size selectivity results for white croaker fitted well with those from the sea trial experiments, which enabled us to use the model established to predict the size selectivity of diamond-mesh codends with a mesh size ranging from 15 to 90 mm and the effect on the exploitation pattern of the species in the fishery by changing the codend mesh size.

Glucocorticoids are key regulators of vertebrate physiology, orchestrating metabolic, immune, and developmental processes that enable adaptation to stress. In teleosts, cortisol is the primary glucocorticoid, acting through classical genomic pathways and rapid non-genomic mechanisms. Although genomic signaling has been widely characterized, non-genomic actions remain poorly understood in skeletal muscle, a tissue of both biological and economic importance. In this study, we examined the effects of cortisol and its membrane-impermeable analog, cortisol-BSA, on rainbow trout (Oncorhynchus mykiss) skeletal muscle under in vivo and in vitro conditions. Transcript analysis demonstrated that cortisol and cortisol-BSA rapidly induced pax3 (2.28 ± 0.22- and 2.48 ± 0.45-fold change, respectively) and myf5 expression (3.03 ± 0.47- and 2.31 ± 0.29-fold change, respectively) at 1 h, whereas prolonged cortisol and cortisol-BSA exposure resulted in their downregulation (0.34 ± 0.07- and 0.38 ± 0.14-fold change, respectively). In cultured myotubes, cortisol-BSA activated protein kinase A (PKA) (2.24 ± 0.25-fold change) and enhanced phosphorylation of its downstream target CREB (3.2 ± 0.21-fold change) in a time-dependent manner; these effects were abolished by the PKA inhibitor H89. Moreover, inhibition of PKA signaling suppressed cortisol-BSA–induced pax3 and myf5 expression (1.31 ± 0.28-fold change and 1.89 ± 0.28-fold change, respectively). Together, these findings provide the first mechanistic evidence that non-genomic cortisol signaling regulates the PKA–CREB axis in fish skeletal muscle, promoting the early transcriptional activation of promyogenic factors. This work underscores the complementary role of rapid cortisol actions in fine-tuning myogenic responses under acute stress, offering new perspectives on muscle plasticity in teleosts.

Greater amberjack (Seriola dumerili) are large reef fish important in fisheries in the southeastern USA, with the Gulf of America stock unsustainably harvested over most of the past two decades. Its age-based stock assessment and recovery plan depend on age and growth information. In this study, 7658 greater amberjack were sampled from the west coast of Florida and off Alabama, Mississippi, and Louisiana in the Gulf from 1991 to 2018. Fish were aged using cross-sectioned sagittal otoliths, with accompanying data on their length, sex, location (state), and type of fishery. Overall, the greater amberjack that were landed in the recreational and commercial fisheries were between 2 and 19 years of age, with the majority between 3 and 5 years old (>80%), and were primarily caught using hook-and-line gear (95%). Sex- and state-specific growth differences were evident based on von Bertalanffy growth models, with females significantly larger at age than males in both Florida and Louisiana (which included Mississippi and Alabama due to low sample size), and females in Louisiana larger at age than females in Florida. Sex ratios in the recreational catches of Florida and Louisiana were skewed towards females (>1.5 female per male), especially for fish ≥1000 mm fork length (>2.3 female per male). Accounting for sex-specific and region-specific growth differences may, in part, help to explain the notably high variability in the overall growth model for greater amberjack in the Gulf.