Low salinity negatively affects early larval development of Nile tilapia, Oreochromis niloticus: insights from skeletal muscle and molecular biomarkers

The Biological, Histopathological, and Parasitic Abundance of Oreochromis niloticus Inhabiting Two Different Freshwater Canals

The current study aimed to assess the impact of metal pollution in water on parasitic abundance, biology, and histopathological characteristics of Oreochromis niloticus in two different freshwater habitats in the Al Sharkia government. The fish were collected from the Mueweis canal area (A) which received industrial wastewater from factories and the San El-Hagar area (B) which received agricultural and domestic wastewater. Parasitic abundance and histopathological changes in the liver and gonads were inspected. The total prevalence of parasitic infection was at the highest percentage in area B correlated with metals present in the water, in addition to severe histopathological damage to the liver and the gonads. The prevalence of parasites for different examined fish ranges from 50% for parasites in the San El-Hagar canal and 4.17% for parasites in the Muwies canal, seasonally. There were positive relationships between Fe or Zn or Mn concentrations with parasite abundance in tilapia fish collected from the San Hagar canal. Several histopathological alterations were detected in the liver and gonads of O. niloticus collected from the two canals located in the Al Sharkia province. It was concluded that the uncontrolled inputs of agricultural and domestic wastes highly altered the O. niloticus health status and the prevalence of the parasites in the investigated two areas.

Morphological and Molecular Responses of Lateolabrax maculatus Skeletal Muscle Cells to Different Temperatures

Temperature strongly modulates muscle development and growth in ectothermic teleosts; however, the underlying mechanisms remain largely unknown. In this study, primary cultures of skeletal muscle cells of Lateolabrax maculatus were conducted and reared at different temperatures (21, 25, and 28 °C) in both the proliferation and differentiation stages. CCK-8, EdU, wound scratch and nuclear fusion index assays revealed that the proliferation, myogenic differentiation, and migration processes of skeletal muscle cells were significantly accelerated as the temperature raises. Based on the GO, GSEA, and WGCNA, higher temperature (28 °C) induced genes involved in HSF1 activation, DNA replication, and ECM organization processes at the proliferation stage, as well as HSF1 activation, calcium activity regulation, myogenic differentiation, and myoblast fusion, and sarcomere assembly processes at the differentiation stage. In contrast, lower temperature (21 °C) increased the expression levels of genes associated with DNA damage, DNA repair and apoptosis processes at the proliferation stage, and cytokine signaling and neutrophil degranulation processes at the differentiation stage. Additionally, we screened several hub genes regulating myogenesis processes. Our results could facilitate the understanding of the regulatory mechanism of temperature on fish skeletal muscle growth and further contribute to utilizing rational management strategies and promoting organism growth and development.

Survival, Growth, and Development in the Early Stages of the Tropical Gar Atractosteus tropicus: Developmental Critical Windows and the Influence of Temperature, Salinity, and Oxygen Availability

Alterations in fish developmental trajectories occur in response to genetic and environmental changes, especially during sensitive periods of development (critical windows). Embryos and larvae of Atractosteus tropicus were used as a model to study fish survival, growth, and development as a function of temperature (28 °C control, 33 °C, and 36 °C), salinity (0.0 ppt control, 4.0 ppt, and 6.0 ppt), and air saturation (control ~95% air saturation, hypoxia ~30% air saturation, and hyperoxia ~117% air saturation) during three developmental periods: (1) fertilization to hatch, (2) day 1 to day 6 post hatch (dph), and (3) 7 to 12 dph. Elevated temperature, hypoxia, and hyperoxia decreased survival during incubation, and salinity at 2 and 3 dph. Growth increased in embryos incubated at elevated temperature, at higher salinity, and in hyperoxia but decreased in hypoxia. Changes in development occurred as alterations in the timing of hatching, yolk depletion, acceptance of exogenous feeding, free swimming, and snout shape change, especially at high temperature and hypoxia. Our results suggest identifiable critical windows of development in the early ontogeny of A. tropicus and contribute to the knowledge of fish larval ecology and the interactions of individuals × stressors × time of exposure.