Fishes

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.

Effective fisheries management relies on accurate stock assessments to ensure sustainable exploitation and long-term ecosystem stability. Fisheries from the Nile Delta lakes of Egypt—comprising Manzala, Burullus, Edku, and Mariout—are economically critical, collectively contributing about 40% of the nation’s total capture fisheries and are facing severe anthropogenic challenges. This study assessed the stock status of 10 key fish species and two crustacean species from these four Nile Delta lakes by determining their life history parameters and exploitation levels. The analysis included estimation of the Length–Weight Relationship (LWR), von Bertalanffy Growth Function (VBGF) parameters, instantaneous mortality coefficients (Z, M, F), and the exploitation ratio (E). Asymptotic total length (L∞) varied widely, ranging from 10.47 cm for Portunus pelagicus to 86.78 cm for Clarias gariepinus (in Lake Manzala). The growth coefficient (K) spanned from 0.31 yr⁻¹ (C. gariepinus) to 1.79 yr⁻¹ (Metapenaeus stebbingi), reflecting diverse life history strategies. The key finding, based on the Gulland criterion, is that all commercial stocks examined in the Nile Delta lakes are currently subjected to severe overexploitation, with the exploitation ratio (E) consistently exceeding the optimal threshold of 0.5. These results underscore the urgent need for adaptive management strategies, including stricter gear regulations and improved fisheries monitoring, to ensure the sustainability of these vital resources.