Osmoregulatory responses in the neotropical fish species Astyanax lacustris, exposed to single and combined microplastics, polycyclic aromatic hydrocarbons, and their mixture.

Microplastic (MP) pollution poses a significant environmental threat. These MPs can adsorb toxic compounds such as polycyclic aromatic hydrocarbons (PAH), which are highly lipophilic and carcinogenic. To assess the potential effects of virgin MP, PAH, and MP+PAH in association with osmoregulation and energetic substrate, we conducted experiments with the tetra cardinal Astyanax lacustris. The environmentally relevant concentration of MP (10 mg L-1) and 20 % of the LC50-96 h of crude oil for A. lacustris (2.28 µg L-1) were used during the 96-h exposure. Fish were exposed to virgin MP, PAH, MPC (MP loaded with PAH), PAH+MP (PAH and MP in association), and the control without (CT) and with handling (CH). After 96 h, blood was collected for osmoregulatory parameters (plasma osmolality; Na+, K+, Cl-, Mg2+; glycose and lactate); gills for osmoregulatory enzyme activities (Na+, K+ ATPase, H+ ATPase, and carbonic anhydrase); and white muscle samples were used to determine glycogen as an energetic substrate. The low molecular weight PAH was not detected in PAH-loaded MP (MPC) and PAH in combination with MP (PAH+MP). The PAH concentration of the MPC and PAH+MP was similar and low compared to other works. Virgin MP, PAH, MPC, and PAH+MP were able to cause muscle glycogen depletion. The activity of v-type H+ ATPase and plasma Na+ concentrations were lower in PAH with MP (MPC). However, the hydromineral balance (K+, Mg2+, Cl-, and osmolality) was not affected by any treatment. In this sense, we can conclude that the MPC caused osmoregulatory disturbances not seen in the MP associated with PAH (MP+PAH). However, this seems unrelated to the PAH leaking from the MPC or the PAH absorption to the virgin MP once the PAH concentrations from the MPC and PAH+MP were similar.

Skin extract from Rhamdia quelen (Siluriformes: Heptapteridae) does not promote stress in conspecifics

Chemical communication is widely used in aquatic environments, where visual or auditory signals may not be always effective. Fish of the superorder Ostariophysi are known to display epidermal cells (club cells) that produce and store alarm substances, which are released to the water when the skin is damaged. Responses to alarm substances range widely, between active searches for refuge to a complete stop in any locomotor activity. In this study a large number of binucleated club cells (average density of 11 cells /5m2) were histologically observed in the skin of the catfish Rhamdia quelen (known as jundia). Skin extract (2, 5, and 10% w/v) applied for 15 minutes to conspecifics elicited increase in swimming activity and in the area visited by the fish inside the tank. However, exposure to the epithelial alarm cue did not evoke any stress response: plasma osmolality, ions (sodium, chloride, magnesium, and potassium), glucose and cortisol remained unchanged. In conclusion, the conspecific alarm cue of the jundia induces behavioral responses but not an acute stress response upon short-term exposure, compatible with its role in fostering physical integrity without representing major stress activation. Considering that in the natural environment such stimuli must quickly disappear due to dilution and that rapid protection responses may be necessary upon the possibility of an approaching predator, a faster mechanism to assure survival may come into play, such as sympathetic nervous system activation. Comunicagco qummica i amplamente utilizada por animais que vivem em ambiente aquatico, onde sinais visuais e auditivos nem sempre sco facilmente identificados. Os Ostariophysi sco conhecidos por apresentarem cilulas club na epiderme, as quais produzem e estocam substbncia de alarme que sco liberadas para o ambiente quando a pele i lesionada. As respostas dos peixes a substbncia de alarme variam entre exploragco ativa por refzgios ati a parada completa de atividade locomotora. Neste estudo, grande nzmero de cilulas club binucleadas (densidade midia de 11 cilulas/5m2) foram histologicamente observadas na epiderme do jundia, Rhamdia quelen. Peixes expostos a extrato de pele de conspecmficos (2, 5, e 10% peso/vol) por 15 minutos apresentaram aumento da atividade locomotora e da area de dispersco. No entanto, essa exposigco nco promoveu nenhuma resposta de estresse - osmolalidade plasmatica, mons (ssdio, cloreto, magnisio e potassio), glicose e cortisol nco sofreram alteragco. Conclummos que a exposigco aguda a extrato de pele de conspecmficos promovem respostas comportamentais de fuga, que essa espicie apresenta grande concentragco de cilulas club, as quais devem estar envolvidas nessas respostas e que a exposigco aguda ao estmmulo nco promoveu respostas bioqummicas indicativas de estresse. Considerando que no ambiente natural tais estmmulos devem desaparecer rapidamente dados a diluigco do meio e que respostas rapidas de protegco devem ser desencadeadas frente ` possibilidade de presenga de predador, vias rapidas de suporte a essas respostas, como sistema nervoso simpatico, por exemplo, devem estar envolvidos.