Moving with the beat: heart rate and visceral temperature of free-swimming and feeding bluefin tuna

Abstract

Owing to the inherent difficulties of studying bluefin tuna, nothing is known of the cardiovascular function of free-swimming fish. Here, we surgically implanted newly designed data loggers into the visceral cavity of juvenile southern bluefin tuna (Thunnus maccoyii ) to measure changes in the heart rate ( f H ) and visceral temperature (T V ) during a two-week feeding regime in sea pens at Port Lincoln, Australia. Fish ranged in body mass from 10 to 21 kg, and water temperature remained at 18-198C. Pre-feeding f H typically ranged from 20 to 50 beats min K1. Each feeding bout (meal sizes 2-7% of tuna body mass) was characterized by increased levels of activity and f H (up to 130 beats min K1 ), and a decrease in T V from approximately 20 to 188C as cold sardines were consumed. The feeding bout was promptly followed by a rapid increase in T V , which signified the beginning of the heat increment of feeding (HIF). The time interval between meal consumption and the completion of HIF ranged from 10 to 24 hours and was strongly correlated with ration size. Although f H generally decreased after its peak during the feeding bout, it remained elevated during the digestive period and returned to routine levels on a similar, but slightly earlier, temporal scale to T V . These data imply a large contribution of f H to the increase in circulatory oxygen transport that is required for digestion. Furthermore, these data oppose the contention that maximum f H is exceptional in bluefin tuna compared with other fishes, and so it is likely that enhanced cardiac stroke volume and blood oxygen carrying capacity are the principal factors allowing superior rates of circulatory oxygen transport in tuna.

Cardiac function in an endothermic fish: cellular mechanisms for overcoming acute thermal challenges during diving

“…It took approximately 3 min for the temperature to change and for the recordings to be stable at the new temperature. After recording Ca 2þ transients and APs at 0.5 Hz, contraction frequency was increased to 1.0 Hz, which is physiologically relevant at 288C [10,13]. Temperature was then decreased to 88C and frequency was dropped to 0.2 Hz.…”

“…Based on archival tag data [5,40] and in vivo heart rate data from freeswimming tuna [10,13], we set our acute temperature change profile from 8 to 288C across cardiac frequencies of 0.2-1.0 Hz (12-60 bpm). Myocytes were perfused initially at the bluefin tuna's acclimation temperature of 148C and stimulated to contract at 0.5 Hz with a field stimulator for Ca 2þ experiments, or the patch pipette for electrophysiology experiments.…”

“…Behavioural records from electronic tags indicate bounce diving in juvenile and adult tuna [2,6,7], whereby animals dive repeatedly to depth to forage and then rapidly resurface (figure 1). Bluefin tunas are the most endothermic lineage of the Thunnus genus; their countercurrent heat exchangers conserve metabolic heat in the brain, eyes, slow-oxidative red muscles [8,9] and viscera [10], which contributes to their wide oceanic range. Among Thunnus only the bluefin lineage ventures into sub-polar and polar seas, and electronic tags in Atlantic bluefins have shown remarkable prolonged occupation of cool surface waters (8-118C), indicative of a high degree of thermal tolerance [2,11].…”

Effects of body mass on physiological and anatomical parameters of mature salmon: evidence against a universal heart rate scaling exponent

“…The functioning and surgical implantation of biologgers have been detailed previously (Clark et al, 2008c;Clark et al, 2009;Clark et al, 2010). On 27 October 2008, individual fish were dip-netted and placed into an anaesthetic bath containing 100mgl -1 tricaine methanesulfonate (MS222; Sigma, St Louis, MO, USA) and 200mgl -1 sodium bicarbonate (NaHCO 3 ) to buffer pH.…”

“…To circumvent some of the above constraints, the present study used implantable biologging technology (see Clark et al, 2008c;particularly for males, give rise to nearly an order of magnitude range in M b among individuals at the same level of sexual maturity, which provides a novel opportunity to examine the intra-specific effects of M b on the physiology and behaviour of wild fish.…”