Best practices for non‐lethal blood sampling of fish via the caudal vasculature

Abstract

Blood sampling through the caudal vasculature is a widely used technique in fish biology for investigating organismal health and physiology. In live fishes, it can provide a quick, easy and relatively non-invasive method for obtaining a blood sample (cf. cannulation and cardiac puncture). Here, a general set of recommendations are provided for optimizing the blood sampling protocol that reflects best practices in animal welfare and sample integrity. This includes selecting appropriate use of anaesthetics for blood sampling as well as restraint techniques for situations where sedation is not used. In addition, ideal sampling environments where the fish can freely ventilate and strategies for minimizing handling time are discussed. This study summarizes the techniques used for extracting blood from the caudal vasculature in live fishes, highlighting the phlebotomy itself, the timing of sampling events and acceptable blood sample volumes. This study further discuss considerations for selecting appropriate physiological metrics when sampling in the caudal region and the potential benefits that this technique provides with respect to long-term biological assessments. Although general guidelines for blood sampling are provided here, it should be recognized that contextual considerations (e.g., taxonomic diversity, legal matters, environmental constraints) may influence the approach to blood sampling. Overall, it can be concluded that when done properly, blood sampling live fishes through the caudal vasculature is quick, efficient and minimally invasive, thus promoting conditions where live release of focal animals is possible.

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“…Alternatively, for a trait like ODBA for which sources of measurement error in sharks are understood, observed variability is likely due to accelerometers being too large 42 , dorsal fins of neonates not being rigid enough for attachment 43 , and the brevity of monitoring that precluded us from accounting for circadian activity rhythms. Among haematological traits, variability in blood pH, for instance, can result because arterial blood cannot be selectively sampled in elasmobranch fishes using caudal puncture 44 . Variation in ṀO 2Min and ṀO 2Max fell within www.nature.com/scientificreports/ ranges reported in teleost fishes, whilst variation in aerobic scope was greater 32 .…”

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“…This method, colloquially known as the “grab‐and‐stab” technique, always involves at least some handling stress, as the fish must first be netted from a holding tank and restrained prior to drawing blood (Clark et al., 2011). In many cases, fish are also euthanized with an overdose of anaesthetic (e.g., MS‐222) prior to drawing blood—a process which undoubtedly disturbs baseline physiological condition (although see Lawrence et al., 2020 for a recent review on non‐lethal blood sampling in fish). Handling stress, although unavoidable, makes it difficult to capture the resting haematological profile of free‐ranging fish and potentially masks underlying baseline changes in haematological variables, particularly if the changes are subtle.…”

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