Studies determining baseline hematological reference intervals (RI) in elasmobranchs are very limited. In this study, blood samples were collected from 94 clinically healthy Nursehound Shark (Scyliorhinus stellaris) maintained under human care. Median (RI) in major leukocyte types were similar to other Carcharhinid sharks as lymphocytes were the predominant leukocyte with 38.0 (28.2–53.5)%, followed by coarse eosinophilic granulocytes with 20.0 (12.2–31.7)%, fine eosinophilic granulocytes with 6.0 (1.2–12.8) %, monocytes with 2.0 (0.0–6.0)%, and neutrophils with 2.0 (0.0–6.0)%. Nursehound Shark produced granulated thrombocytes, which were classified as granulocytes and represented 28.5 (12.4–39.7)% of all leukocytes. Median (RI) manual red blood cell and white blood cell counts were 177.50 (132.50–210.00) x 10⁹ cells/l and 8.26 (5.24–14.23) x 10⁹ cells/l, respectively. Median (RI) plasma chemistry values showed alkaline phosphatase 7.7 (4.2–13.0) U/l, aspartate aminotransferase 7.6 (3.3–17.1) U/l, blood urea nitrogen 281.6 (261.2–305.0) mmol/l, calcium 3.97 (3.59–4.47) mmol/l, total cholesterol 2.04 (1.02–3.91) mmol/l, chloride 233.0 (215.2–259.0) mmol/l, iron 3.79 (1.74–6.93) μmol/l, glucose 0.87 (0.47–1.44 mmol/l), potassium 3.8 (2.9–4.6) mmol/l, sodium 243.0 (227.7–271.0) mmol/l, phosphorus 1.58 (1.13–2.10) mmol/l, total protein 24.0 (20.0–35.0) g/l, and triglycerides 0.97 (0.49–3.35) mmol/l. Creatine kinase, gamma glutamyl transferase, and lactate dehydrogenase levels were below the instrument reading range.

Infectious and inflammatory diseases are the most frequently diagnosed pathologies in elasmobranchs maintained under human care. Non-steroidal anti-inflammatory drugs (NSAIDs) are frequently used in veterinary medicine for their anti-inflammatory, analgesic, and antipyretic properties. Meloxicam is a commonly prescribed NSAID in elasmobranchs, but there are still no published pharmacokinetic (PK) studies supporting its use in this group of animals. In this study, meloxicam was administered at a single dose of 0.5 mg/kg to eight healthy adult nursehound sharks (Scyliorhinus stellaris) intravenously (IV), intramuscularly (IM), and orally (PO), with a minimum 4-week washout period between administrations. Blood samples were obtained both beforehand and at predetermined times after each administration. Plasma concentrations were measured using a validated high performance liquid chromatography method, and PK data was obtained using a non-compartmental analysis. Meloxicam administered orally did not produce detectable concentrations in blood plasma, while mean peak plasma concentration was 0.38 ± 0.08 μg/ml after IM administration. The mean terminal half-life was 10.71 ± 2.77 h and 11.27 ± 3.96 h for IV and IM injections, respectively. The area under the curve extrapolated to infinity was 11.37 ± 2.29 h·μg/ml after IV injections and 5.98 ± 0.90 h·μg/ml after IM injections. Meloxicam administered IM had a mean absolute bioavailability of 56.22 ± 13.29%. These numbers support meloxicam as a promising drug to be used IM in nursehounds, questions the efficacy of its single PO use in elasmobranchs, elucidate the need for higher dosage regimes, and evidence the need for further PK studies in sharks and rays.

Background: This study determined plasma protein electrophoresis (PPE) reference intervals in two elasmobranch species: the undulate skate (Raja undulata) and the nursehound shark (Scyliorhinus stellaris), using a reference population of 48 undulate skates (27 males, 21 females) and 62 nursehounds (32 males, 30 females), considered to be clinically healthy. Plasma samples were analyzed using capillary zone electrophoresis (CZE). Results: The undulate skate electrophoretogram resembled those previously reported in other batoids and could be divided into seven consistent fractions. No statistically significant differences were detected between sexes and developmental stages. The nursehound electrophoretogram was similar to that previously described in other shark species and could be divided into eight consistent fractions. Fraction 5% was significantly higher in juvenile nursehounds when compared to adults, while fraction 6 concentration and percentage were significantly higher in adults. Fraction 4% was higher in males than in females. Albumin band was not detected, and pre-albumin was negligible in both studied species. Alpha-globulins were predominant in the undulate skate, while beta-globulins were predominant in nursehounds. Statistically significant differences were found in all electrophoretogram fraction percentages and concentrations between the two species. Conclusion: To the authors knowledge, this is the first study reporting PPE values in undulate skates and nursehounds, and the first study using CZE in elasmobranch plasma. These findings can serve as a primary reference for health monitoring in both species and will add to the limited data available on PPE in elasmobranchs.

A single-dose meloxicam pharmacokinetic (PK) study was performed with eight clinically healthy nursehound sharks (Scyliorhinus stellaris) maintained under human care. Meloxicam was administered IM at a dosage of 1.5 mg/kg to six animals; two animals were administered elasmobranch physiological saline solution (EPSS) IM as a negative control group. Blood samples were obtained prior to and at 12 predetermined times during the first 36 h after administration. Effects on hematology and plasma biochemistry were compared prior to and 24 h after administration. No animal died or showed clinical signs during the study. A significant increase in creatinine kinase and aspartate aminotransferase was found in both EPSS and meloxicam groups and could be considered a direct consequence of sampling and handling required for the PK study. Observed mean time to maximum plasma concentration ± SEM was 2.58 ± 0.47 h and observed mean maximum plasma concentration ± SEM was 806 ± 66 ng/ml; mean terminal half-life ± SEM was 15.97 ± 1.20 h; mean residency time ± SEM was 23.40 ± 2.25 h. Area under the plasma concentration–versus-time curve extrapolated to infinity ± SEM was 15.52 ± 1.70 h·µg/ml. This study suggests that meloxicam 1.5 mg/kg IM in nursehound sharks is likely to result in clinically relevant plasma levels for periods of 24 h without producing significant alterations in blood analytics, although further PK studies with meloxicam IV in sharks are needed. Future PK and pharmacodynamic studies with different drugs and doses are needed in elasmobranchs to establish safe and effective treatment protocols.

Blood analysis represents a crucial, yet often underutilized, diagnostic tool in elasmobranch medicine. Its broader application has been limited by the absence of standardized protocols and consistent species-specific reference values. The variability in sampling techniques, analytical methods, and data interpretation presents significant challenges for both clinical practices and cross-institutional research. This manuscript offers a comprehensive, evidence-based guideline for blood collection and analysis in elasmobranchs. It details best practices for documenting biological and procedural metadata to enhance sample comparability and provides practical recommendations for venipuncture site selection, blood gas analysis, hematology, biochemistry, and plasma protein electrophoresis. The techniques described are optimized for use with materials and equipment commonly found in veterinary settings. The adoption of these standardized protocols is expected to improve diagnostic accuracy, facilitate the development of reliable species-specific reference ranges, and enable the integration of health data across facilities. Routine implementation in monitored populations is encouraged to set reliable reference physiological levels, support early disease detection and advance veterinary care, as well as contribute to the broader field of elasmobranch health, research and conservation.

Despite the paucity of published literature on elasmobranch hematology and biochemistry, great interspecific diversity has been observed. Blood samples from 43 undulate rays (Raja undulata) (23 males, 20 females) hatched and raised at Oceanogràfic Aquarium, were analyzed for hematology and plasma biochemistry. Animals were divided into two age groups: 1 yr old (28 skates) and 2 yr old (15 skates). All individuals were clinically healthy on physical examination. Weight, total length, standard length, and disc width were recorded. No statistically significant differences were observed between male and female juvenile skates for the evaluated morphometric, hematologic, and plasma biochemical values. Once reference intervals (RI) were determined, blood samples from seven healthy adult skates housed at the same aquarium were collected for comparison. Statistically significant differences were observed in cholesterol, triglycerides, alkaline phosphatase, blood urea nitrogen, chloride, and sodium between juvenile and adult skates. This is the first article describing hematological and plasma biochemical RI for this species, increasing the clinical knowledge on elasmobranch blood analytics. These data will serve as a valuable diagnostic and research tool for professionals working with undulate rays and closer relatives in aquariums and in the field. Further studies using larger elasmobranch sample sizes are needed to determine reliable species-specific baseline health values and to evaluate the effect of intrinsic and extrinsic parameters on blood analytics more accurately.