Abstract
ABSTRACTCardiovascular performance is altered by temperature in larval fishes, but how acute versus chronic temperature exposures independently affect cardiac morphology and physiology in the growing larva is poorly understood. Consequently, we investigated the influence of water temperature on cardiac plasticity in developing mahi-mahi. Morphological (e.g. standard length, heart angle) and physiological cardiac variables (e.g. heart rate fH, stroke volume, cardiac output) were recorded under two conditions by imaging: (i) under acute temperature exposure where embryos were reared at 25°C up to 128 h post-fertilization (hpf) and then acutely exposed to 25 (rearing temperature), 27 and 30°C; and (ii) at two rearing (chronic) temperatures of 26 and 30°C and performed at 32 and 56 hpf. Chronic elevated temperature improved developmental time in mahi-mahi. Heart rates were 1.2–1.4-fold higher under exposure of elevated acute temperatures across development (Q10≥2.0). Q10 for heart rate in acute exposure was 1.8-fold higher compared to chronic exposure at 56 hpf. At same stage, stroke volume was temperature independent (Q10∼1.0). However, larvae displayed higher stroke volume later in stage. Cardiac output in developing mahi-mahi is mainly dictated by chronotropic rather than inotropic modulation, is differentially affected by temperature during development and is not linked to metabolic changes.
Highlights
Recruitment of fish populations is highly dependent upon environmental conditions encountered during early life-history stages (Houde, 1989; Rijnsdorp, 2009; Wexler et al, 2007)
Temperature influence on embryo-larval morphology Standard body length increased with development (Fig. 1A, ANOVA, P=0.005)
Mahi-mahi chronically raised at 30°C (4.72±0.04 mm) were longer than those chronically raised at 26°C (4.56±0.04 mm) (Fig. 1B, P=0.02)
Summary
Recruitment of fish populations is highly dependent upon environmental conditions encountered during early life-history stages (Houde, 1989; Rijnsdorp, 2009; Wexler et al, 2007). The sensitivity of embryos and larvae may be explained by their small size, incomplete morphological and physiological development, high dynamic metabolic rate, low energy reserves, small migration capacities (little or no swimming activity) and their heavy dependence on ambient environmental conditions (dissolved oxygen, temperature, pH, etc.) (Finn and Kapoor, 2008). Developing fish, in particular, have a narrower thermal window than the later stages of their life history, making them vulnerable to temperature changes (Pelster, 1999; Pörtner and Farrell, 2008; Pörtner et al, 2001; Rijnsdorp, 2009)
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