Ontogeny of regional endothermy in Pacific bluefin tuna (Thunnus orientalis)

• Published in: Marine biology Vol. 167; no. 9
• Main Authors: Malik, Arif, Dickson, Kathryn A., Kitagawa, Takashi, Fujioka, Ko, Estess, Ethan E., Farwell, Charles, Forsgren, Kristy, Bush, Jeannette, Schuller, Kathryn A.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 27.08.2020; Springer; Springer Nature B.V
• Subjects: Allometry; Biomedical and Life Sciences; Blood vessels; Bluefin tuna; Body mass; Coefficients; Cranium; Fishes; Fork length; Freshwater & Marine Ecology; Life Sciences; Marine & Freshwater Sciences; Marine biology; Mass; Microbiology; Muscles; Oceanography; Ontogeny; Original Paper; Scaling; Skeletal muscle; Skull; Thunnus orientalis; Tuna; Viscera; Water temperature; Zoology; Pacific Ocean; California
• ISSN: 0025-3162; 1432-1793
• DOI: 10.1007/s00227-020-03753-3

Tunas can elevate their red (slow-twitch, oxidative) skeletal muscle, visceral and cranial temperatures significantly above the ambient water temperature ( T a ) with the aid of specialized blood vessels ( retia mirabilia ) that conserve metabolic heat. The ontogeny of this phenomenon, known as regional endothermy, was studied in young [18.5–62.5 cm fork length (FL), 71–5350 g body mass, 2–16 months of age] Pacific bluefin tuna ( Thunnus orientalis ). Maximal red muscle, visceral and cranial temperatures were measured in parallel with measuring red muscle mass and the size of the red muscle and visceral retia . The maximal thermal excess (maximal tissue temperature – T a ) increased from 1.1 ± 0.3 °C (mean ± SD) to 11.1 ± 3.4 °C in the red muscle, from 0.6 ± 0.3 °C to 3.5 ± 1.4 °C in the viscera and from 0.5 ± 0.4 °C to 2.0 ± 0.6 °C in the cranium in the smallest individuals compared with the largest. Thus, red muscle endothermy was well developed, but visceral and cranial endothermy were still developing, in the largest individuals studied. The scaling coefficients, relative to body mass, for total red muscle mass (0.90 ± 0.03, mean ± SE), red muscle rete (RMR) length (0.84 ± 0.06), maximum number of RMR blood vessel rows (0.43 ± 0.04) and visceral rete cross-sectional area (0.90 ± 0.08), indicated negative allometry for total red muscle mass (< 1.0) but positive allometry for the length of the red muscle retia (> 0.33) and the area of the visceral rete (> 0.67).