Browsing by Author "Valle, Michela della"
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- Toxic impacts in mucus of Halobatrachus didactylus: modulation of activity by fish’s sex, stress and environmental conditionsPublication . Valle, Michela della; Guerreiro, Pedro Miguel Guerreiro da Costa; Modesto , Teresa Isabel MendonçaHalobatrachus didactylus, commonly known as the Lusitanian toadfish, is a benthic sedentary species inhabiting coastal waters, which mucus was recently found to have toxic activity over bacteria and other fish, likely playing a role as an immune and defense mechanism. This study aimed to investigate which conditions, intrinsic or external, may determine the toxicity of the mucus over other fish species, including amount, stress, sex and salinity, while understanding the potential role of the skin and axillary glands in toxin production. Through a series of in vivo and in vitro experiments, the toxicity of the mucus was evaluated using Sparus aurata and Gambusia holbrooki as test subjects. The experiments showed that the lethal effect of the toxin is dose dependent, either when collected mucus was added to water or when toadfish holding water was used. The results also revealed that male mucus have higher toxicity than female mucus, reflected in higher lethality of test subjects exposed to the same conditions. Haemolytic activity experiments showed differences in toxicity between sexes, with male mucus causing higher hemolytic activity. The toxin is likely hydrophilic as it maintains activity in the toadfish holding water, but environmental salinity was found to influence the toxin’s effectiveness: mucus added to seawater was effective while freshwater conditions nullified the mucus's lethality, suggesting that the toxin may require specific environmental conditions or physiological pathways to be active to evoke an effect. While the skin mucus clearly demonstrated toxic properties, no significant toxic effect was detected from the contents of the axillary glands, challenging the hypothesis of their involvement in toxin production. The histological analysis revealed a higher density of skin mucus cells in males compared to females, raising questions about sex-based physiological differences in mucus production and toxicity. This research provides new insights into the toxicological properties of H. didactylus and suggests that its mucus plays a dual role in predation defense and microbial protection. However, further biochemical analyses are required to fully understand the molecular composition of the toxin, actual sites and regulatory mechanisms of secretion, and its ecological significance.