Impacts of acute hypoxia on the short-snouted seahorse metabolism and behaviour.

Seahorses are one of the most unique and enigmatic animals, recognized as flagship species for several conservation issues. Unfortunately, seahorses' populations have been declining and their unique lifestyle may constrain the ability of these animals to evolve in the future climate scenarios. They inhabit shallow coastal waters that display daily or seasonal environmental fluctuations. Yet, few studies have scrutinized the impacts of climate changes on these iconic species. Within this context, the objective of this work was to test the effects of an extreme hypoxia exposure (~27 % dissolved oxygen for approximately 7 h) on the metabolism, behaviour and food intake of the temperate seahorse Hippocampus hippocampus. Regarding metabolism, hypoxia exposure led to a significant reduction in metabolic rates and an increase in ventilation rates. Seahorses showed signs of movement lethargy under oxygen depletion. The results show that a small but extreme exposure to hypoxia is tolerable by seahorses despite inducing metabolic and behavioural changes, that may jeopardize the future development and survival of these iconic organisms.

Blood collection under anesthesia, peripheral blood cells, plasma biochemistry, and plasma protein electrophoresis in a living fossil: the Spotted Ratfish (Hydrolagus colliei).

This report describes the safe and effective handling under anesthesia, blood collection and main clinical pathology values determination for three adult Spotted Ratfish (Hydrolagus colliei) (two males and one female) successfully maintained under human care for more than 20 years. The anesthetic MS-222 diluted in tamponed salt water at 50 ppm provided deep narcosis with mean induction and recovery times of 5 and 20 min, allowing safe handling and blood collection in the three animals sampled. Major leukocyte types were similar to other teleost and elasmobranch species, identifying lymphocytes as the predominant leukocyte (75.5%), followed by the fine eosinophilic granulocytes (10.25%), the coarse eosinophilic granulocytes (9.75%), and a small percentage of monocytes (5.50%). Plasma biochemistry values in this species were like those seen in elasmobranchs, with the highest levels of blood urea nitrogen described in any Chondrichthyes (mean 679.7 mmol/l). Plasma protein electrophoresis analysis in the Spotted Ratfish showed five consistent fractions, like those previously described in other fish species, with a negligible quantity of proteins migrating in the region equivalent to albumin, and with fraction 4 (mean 53.20%) as the predominant fraction. Despite the limitations imposed by the small sample size and the challenging access to the studied species under human care, this study will shed light on and enhance clinical knowledge regarding Ratfish handling, anesthesia, blood collection, and analysis. It aims to deliver a comprehensive clinical pathology description, presenting valuable data for professionals engaged in the care and management of Chimaerans.