Effects of temperature and oxygen availability on blood parameters and erythrocyte and leucocytes distribution in Halobatrachus didactylus

JUAN MANUEL MOLINA; ANDREAS KUNZMANN; JOÃO PENA REIS; PEDRO GUERREIRO

Congreso; 14th International Congress on the Biology of Fish (ICBF); 2022

Temperature and oxygen are two of the most affected environmental variables in our age of climate.The changes in these variables can have a plethora of effects on marine biota, and understandingthem is of outmost importance to address this issue. We simulated climate change scenarios, toevaluate the effects of high temperature, hypoxia and a combination of both, on blood parametersand cell proportions of Halobatrachus didactylus.We used a condition index to estimate the welfare of the fish in each treatment. The twoenvironmental drivers studied showed effects on the number of white blood cells and shape of redblood cells over the course of 30 days of exposure. The most affected parameter was the red andwhite blood cell count, which increased significantly in hypoxic conditions. Hematocrit increasedsignificantly in hypoxic conditions. Hemoglobin concentration was unaffected by our treatments. Redblood cell counts were higher in high temperature, but oxygen levels showed no effects on thisparameter, which leads us to believe hypoxia triggers an increase in white cell numbers. Blood pHwas significantly lower in the high temperature normoxic scenario in comparison to all othertreatments.These changes seem to have negatively impacted the condition of the fish, as individuals on the hightemperature conditions exhibited much lower condition index values.Supported by Assemble PLUS grant (Project code 8307) the Alexander von Humboldt Foundationawarded to JMM. Funds from FCT – Portuguese Foundation for Science and Technology throughproject UIDB/04326/2020 and EMBRC.PT ALG-01-0145-FEDER-022121. We thank A. Alves, C.Sousa, E. Couto and T. Modesto for help with the fish sampling.