Abstract
We investigated blood gas, hematological and biochemical parameters, and gill morphology of Lophiosilurus alexandri juveniles submitted to hypoxia for 48h, followed by recovery for 48h. A total of 48 juveniles (360.0 ± 141.6g) were distributed among eight tanks (120 L) and subjected to hypoxia condition (water with dissolved oxygen at 2.12 ± 0.90mg L-1) or normoxia (at 5.60 ± 0.31mg L-1). Blood gas values (pH, PvCO2, PvO2, sO2, HCO3-, stHCO3-, and base excess) in hypoxia were significantly different from normoxia, while for lactate and the electrolytes (K+, Na+, Cl-, and Ca2+) there was no significant change among treatments. The erythrocytes differed significantly between normoxia and hypoxia at 72h (24h of recovery), while for hemoglobin and hematocrit there were no significant differences. There was a significant difference in glucose, triglycerides, and cholesterol for both normoxia and hypoxia, while plasma protein remained unchanged. All gill components (epithelial cells, erythrocytes, pillar cells, mucous cells, ionocytes, undifferentiated cells, and blood capillary lumen) differed significantly between normoxia and hypoxia. A reduction in the length of the primary lamella was observed in the hypoxia and recovery treatments, when compared to normoxia. The secondary branchial lamella showed no significant difference for both treatments. Juveniles of Lophiosilurus alexandri adapted well to hypoxia for 48h, as they were able to adjust most of their physiological variables to survive this stress condition. After 48h of hypoxia recovery, fish showed parameters similar to animals in normoxia. Thus, the present study shows that the tolerance to hypoxia conditions of L. alexandri, together with other important beneficial characteristics of the species, such as the high meat quality and high commercial value, demonstrates its great potential for production among regional species.
Highlights
The stress response of fish occurs through neuroendocrine control in a way very similar to that of mammals
Hematological and biochemical parameters and gill morphology and morphometry of Lophiosilurus alexandri juveniles submitted to hypoxia for 48 hours followed by recovery for 48 hours
Blood gas values in hypoxia were significantly different from normoxia, while lactate and the electrolytes (K+, Na+, Cl−, Ca2+ and HCO3−) there was no significant change among treatments
Summary
The stress response of fish occurs through neuroendocrine control in a way very similar to that of mammals. Fish can experience several factors that are considered stressors in captivity, such as high confinement densities (Long et al 2019; Refaey et al 2018; Yarahmadi et al 2016), handling and transportation (Jerez-Cepa et al 2019; Sena et al 2016) and changes in water quality (Lankford et al 2003; Zhang et al 2015). These stressors generate physiological disorders, which cause discomfort, impair well-being and potentially compromise survival. To maintain and restore body homeostasis, a stressed animal consumes energy due to breathing, locomotion and tissue repair, instead of using it for growth, reproduction, food intake and physiological status (Schreck and Tort 2016)
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