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One of the most crucial biological indicators in tracking long-term variations in the reproductive cycle is sexual development. Scorpaena porcus (Linnaeus, 1758), commonly known as the black scorpionfish, is a small teleost from the family Scorpaenidae. Much is known about its ecology, but data on its reproductive and defense systems are still lacking. Antimicrobial peptides (AMPs), such as piscidins, are integral components of the innate immune system in fish. These peptides exhibit a wide range of activity against bacteria, fungi, viruses, and protozoa and act as the first line of host defense. This study aims to investigate the primary sexual development stages in male and female gonads of black scorpionfish, providing additional knowledge on the reproductive biology of this teleost while evaluating concomitant changes in the expression of a Piscidin-1 antimicrobial peptide. The results show a histological, morpho-structural change from the immature stage to the developing virgin stage. Immunohistochemical analyses show that germinal and somatic cells are strongly reactive to Piscidin-1 in both gonads at an early ontogeny stage. These data suggest that Piscidin-1 may play a key role in the local defense system of scorpionfish gonads at this delicate stage, which is critical for the continuation and maintenance of the species. The present findings are potentially useful for a better understanding of the reproductive cycle of this fish, improving our knowledge of the interaction between the immune system and reproduction.

The ubiquitous presence of microplastics (MPs) in the environment is a major concern for the conservation of biodiversity. Numerous studies show the detrimental effects of MPs on marine species, especially because of their small size and their capacity to absorb organic contaminants from their surroundings. The bivalve mollusk Cerastoderma glaucum (Bruguière, 1789), because of its wide geographic distribution and immobile feeding habits, can be used as a sentinel and bioindicator species. By examining the presence, localization, and co-localization of Toll-like receptor 2 (TLR2) and inducible nitric oxide synthetase (iNOS), this study aims to evaluate the response of the internal defense system of C. glaucum to pristine MPs through the employment of confocal microscopy and bioinformatics techniques. The results show haemocytes immunoreactive to the antibodies tested; in particular, a higher number of TLR2-positive haemocytes can be observed in the group exposed to pristine MPs. These findings suggest that haemocytes can play a key biomarker role as sentinels to environmental pollutants. Furthermore, bioinformatics analyses on the antibodies tested confirmed an evolutionary conservation of these molecules. These data highlight the critical role of phagocytosis in identifying ecosystem damage and are helpful in developing biosensors with less negative effects on the environments in which they are applied.