Platypuses (Ornithorhynchus anatinus) inhabit the permanent rivers and creeks of eastern Australia, from north Queensland to Tasmania, but are experiencing multiple and synergistic anthropogenic threats. Baseline information of health is vital for effective monitoring of populations but is currently sparse for mainland platypuses. Focusing on six hematology and serum chemistry metrics as indicators of health and nutrition (packed cell volume (PCV), total protein (TP), albumin, globulin, urea, creatinine, and triglycerides), we investigated their variation across the species’ range and across seasons. We analyzed 259 samples collected from platypuses in three river catchments in New South Wales and Victoria. Health metrics significantly varied across the species’ range, with platypuses from the most northerly catchment, having lower levels of PCV, albumin and triglycerides, potentially reflecting thermal stress. The Snowy River showed significant seasonal patterns which varied between the sexes and coincided with differential reproductive stressors. Male creatinine and triglyceride levels were significantly lower than females, suggesting that reproduction is energetically more taxing on males. Age specific differences were also found, with juvenile PCV and TP levels significantly lower than adults. Additionally, the commonly used body condition index (tail volume index) was only negatively correlated with urea, and triglyceride levels. A meta-analysis of available literature did not reveal any significant latitudinal relationship, but this was confounded by variation in sampling times which is not commonly reported. We provide the first reference intervals of hematology and blood chemistry for mainland platypus, highlighting the importance of considering seasonal variation, enabling future assessments of individual and population health.

Trapping and handling of platypuses was consistent with guidelines approved by the NSW Office of Environmental Heritage (SL101655), NSW Department of Primary Industries (P15/0096=1.0 & OUT15/26392), and UNSW’s Animal Care and Ethics Committee (16/14A). Between January 2016 and May 2018, 259 platypuses were trapped using fyke and gill nets, and anesthetized using isoflurane gas, as described in Bino, et al. ^83,Hawke, et al. ⁸⁴,  in three river catchments across seven rivers in New South Wales; Border Rivers Catchment (Tenterfield Creek n=42, and Severn River n=41, Jan-May 2016), Snowy Rivers Catchment (Eucumbene n=26, Snowy n=90, Thredbo Rivers n=22, Dec 2016-Nov 2017); and Victoria, Upper Murray Rivers Catchment (Mitta Mitta n=18, and Ovens Rivers n=20, Jan-May 2018, Fig. 1). Elevation was calculated using a one second Digital Elevation Models ⁸⁵ for each sample (Severn 393m-819m, Tenterfield 373m-816m, Eucumbene 939m-1336m Snowy 745m-847m, Thredbo 921m-1352m, Mitta Mitta 282-m541m, Ovens 244m-405m). Body condition of each platypus was evaluated using tail volume index (TVI, 1-5 with 1 indicating high levels of fat stored in the tail and 5 indicating low levels), a commonly used qualitative measure of fat reserves ⁸². Sex and age were also determined, based on presence and shape of spurs ^86,87. Blood samples of 2mL were collected from the bill sinus ⁸⁰. Packed cell volume (PCV) and total protein (TP) were determined using a microhematocrit heparinized capillary tube and refractometer, following centrifugation (75mL, 14000 g, 5 min), with the remaining blood centrifuged (2000 g) for 10 minutes to separate serum, which was then stored at -80° C. Chilled serum was analyzed in 2019 by Vetnostics Laboratory, using a Cobas 8000 (Roche diagnostic systems), providing blood serum chemistry data for albumin, urea, creatinine, and triglycerides. Globulin was determined by subtracting albumin from the TP.