Structure, composition, mechanics and growth of spines of the dorsal fin of blue tilapia Oreochromis aureus and common carp Cyprinus carpio

Predicting the potential implications of perch (Perca fluviatilis) introductions to a biodiversity-rich lake using stable isotope analysis

Biological invasions, particularly of fish species, significantly threaten aquatic ecosystems. Among these invaders, the introduction of the European perch (Perca fluviatilis) can have particularly detrimental effects on native communities, affecting both ecosystem functioning and human well-being. In this study, carbon and nitrogen stable isotope analysis was employed, using perch originating from five different ecosystems, to model the effects of their hypothetical introduction into İznik Lake, an economically and ecologically important, biodiversity-rich lake in northern Turkey, to ultimately assess their potential predation impact and competition with native predators. The results revealed that if perch were introduced to the community, they would - considering gape size limitations - primarily prey upon Vimba vimba and Rutilus rutilus, indicating a significant feeding pressure on these species. Furthermore, the study identified a potential overlap and competition for resources between commonly mesopredator perch and the European catfish Silurus glanis, the current top predator in the ecosystem. Both species would occupy top predatory positions, emphasizing the potential disruption of predator-prey dynamics. Our findings underscore the potential ecological repercussions of perch invasions. The selective predation on V. vimba and R. rutilus, with the latter being consumed to a lesser extent by perch, could lead to cascading effects throughout the food web, altering the community structure, and ecosystem dynamics. Additionally, the competition between perch and S. glanis raises concerns about effects on the stability and functioning of the fish community. These results highlight the need for proactive management strategies to mitigate the risk of perch introductions. Strict regulations on the movement and introduction of invasive species, along with comprehensive monitoring, are crucial for preserving native communities and maintaining the ecological integrity of freshwater ecosystems. Our study demonstrates the potential predation impact of perch on vulnerable fish species and the competition with the established apex predator, emphasizing the importance of considering the ecological consequences of perch invasions and informing management decisions to ensure the conservation and sustainability of aquatic ecosystems.

Fin healing and regeneration in sturgeon

Pectoral fin healing in fin spines and rays were examined in juvenile Atlantic sturgeon Acipenser oxyrinchus oxyrinchus following three different sampling techniques (n = 8-9 fish per treatment): entire leading fin spine removed, a 1-2 cm portion removed near the point of articulation, or a 1-2 cm portion removed from a secondary fin ray. Also, to determine whether antibiotic treatment influences healing, an additional group of fish (n = 8) was not given an injection of an oxytetracycline (OTC)-based antibiotic following removal of the entire leading fin spine. Following fin sampling, fish from different treatments were mixed equally between three large (4,000 I) recirculating systems and fin-ray healing and mortality were monitored over a 12 month period. To assess healing, blood samples were collected at 4 months to measure immune system responses, radiographs were taken at 4, 8 and 12 months to assess the degree of calcification in regions of damaged fins and fins were analyzed histologically at 12 months. Fish grew from a mean weight of 1.8 to 3.2 kg during the experiment and survival was near 100% in all treatments, with only one fish dying of unknown causes. Leukocyte counts, an indication of health status and survival were similar among treatments and in groups with or without antibiotic injection. Radiographs revealed mineralization took longer in fish with the entire leading fin spine removed and was the slowest near the point of articulation, presumably due to the greater structural support for the pectoral fin at this location. Histological sampling indicated spines and rays had similar healing patterns. Following injury, an orderly matrix of collagen bundles and many evenly spaced scleroblasts were present, transitioning to Sharpey fibres, with concentric layers forming lamellar bone. Healing and mineralization were characterized as periosteal osteogenesis and included embedded osteocytes surrounded by an osteoid seam. Chondroid formation was apparent in a few fractures not associated with treatments. The duration of time for external wound healing and internal mineralization of spines and rays depended on the fin treatment, with the slowest healing observed in fish with the most tissue removed, the entire leading fin spine.