Establishment of preliminary reference intervals and cytochemical staining of blood cells in big-bellied seahorses (Hippocampus abdominalis).

Background: Despite their popularity, hematology reference intervals (RIs) have not been established in big-bellied seahorses (Hippocampus abdominalis).

Objective: The objectives of this study were to establish hematologic RIs to compare values between sex in regard to cytochemical staining of blood cells. We also sought to compare white blood cell concentrations using the Natt and Herrick technique vs blood smear estimates.

Methods: Forty-three healthy individuals from the Aquarium du Québec (22 females and 21 males) were included. Normal health status was confirmed by an unremarkable physical examination in five individuals and by necropsy of five other individuals, of which all were excluded from further analyses. Venipuncture was performed from the ventral coccygeal vein in the remaining 33 individuals without anesthesia using heparinized insulin syringes. A blood volume of 0.05 to 0.1 ml was collected to prepare Wright Giemsa-stained blood smears and hematocrits immediately after venipuncture. Whole blood was stored in heparinized Eppendorf tubes to determine red and white blood cell concentrations using the Natt and Herrick technique with a hemocytometer in 10 individuals; these results were compared with blood smear estimates. Additional blood smears were stained with alkaline phosphatase substrate, periodic acid Schiff, and toluidine blue stains.

Results: The reference intervals included the packed cell volume (27.4-67.5%), thrombocyte count (19.5-197.7 × 10 /L), and white blood cell (WBC) count (2-54.8 × 10 /L), including neutrophils (1.1-21.3 × 10 /L), lymphocytes (2.7-45.5 × 10 /L), and monocytes (0-2.2 × 10 /L). The WBC hemocytometer counts showed no correlation with blood smear estimates (Spearman's rho = 0.2). There was also no significant difference between the sexes.

Conclusions: These preliminary reference intervals will help assess the health of seahorses.