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McKenzie, D. J., Blasco, F. R., Belão, T. C., Killen, S. S., Martins, N. D., Taylor, E. W., et al. (2017). Physiological determinants of individual variation in sensitivity to an organophosphate pesticide in Nile tilapia Oreochromis niloticus. Aquatic Toxicology, 189(Supplement C), 108–114.
Résumé: Individual variation in sub-lethal sensitivity to the organophosphate pesticide trichlorfon was investigated in Nile tilapia, using critical swimming speed (Ucrit) as an indicator. Tilapia exposed for 96h to 500μgl−1 trichlorfon at 26°C (Tcfn group, n=27) showed a significant decline in mean Ucrit, compared to their own control (pre-exposure) performance in clean water (−14.5±2.3%, mean±SEM), but also compared to a Sham group (n=10) maintained for 96h in clean water. Individuals varied in their relative sensitivity to the pesticide, with the decline in Ucrit after exposure varying from 1 to 41%. The Ucrit of the Tcfn group did not recover completely after 96h in clean water, remaining 9.4±3.2% below their own control performance. The decline in performance was associated with a significant increase in net cost of aerobic swimming, of +28.4±6.5% at a sustained speed of 2bodylengthss−1, which translated into a significant decline in swimming efficiency (Eswim) of −17.6±4.0% at that speed. Within the Tcfn group, individual Eswim was a strong positive determinant of individual Ucrit across all trials, and a strong negative determinant of individual% decline in Ucrit after pesticide exposure (P<0.001, linear mixed effect models). Trichlorfon had no effects on standard metabolic rate or active metabolic rate (AMR) but, nonetheless, individual Ucrit in all trials, and% decline in Ucrit after exposure, were strongly associated with individual AMR (positively and negatively, respectively, P<0.001). Individual Ucrit under control conditions was also a strong positive determinant of Ucrit after trichlorfon exposure (P<0.001), but not of the% decline in Ucrit performance. In conclusion, the OP pesticide impaired Ucrit performance by reducing Eswim but individual tilapia varied widely in their relative sensitivity. Intrinsic individual physiology determined effects of the pesticide on performance and, in particular, good swimmers remained better swimmers after exposure.
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McKenzie, D. J., Hoglund, E., Dupont-Prinet, A., Larsen, B. K., Skov, P. V., Pedersen, P. B., et al. (2012). Effects of stocking density and sustained aerobic exercise on growth, energetics and welfare of rainbow trout. Aquaculture, 338, 216–222.
Résumé: Two stocking densities, “low” (L, between similar to 19 and similar to 25 kg m(-3)) and “high” (H, between similar to 75 and similar to 100 kg m(-3)) were compared for effects on specific growth rate (SGR), feed conversion, energetics and welfare of rainbow trout reared at 14 degrees C either in static water (S) or swimming in a gentle current of similar to 0.9 bodylengths s(-1) (C). Trout (initial mass similar to 110 g) were reared for 9 weeks in circular tanks (volume 0.6 m(3)), in triplicate of four conditions (LS, LC, HS, HC). Fish were fed ad-libitum daily: waste pellets were swirl-collected at the outflow to calculate feed intake. SGR was measured each three weeks for the last six weeks of the trial. The tanks functioned as intermittent-stopped flow respirometers, to permit metabolic rate to be measured as instantaneous oxygen uptake once per hour. Mean (+/-SD) SGR was significantly lower at H than L (1.51 +/- 0.03 vs 1.44 +/- 0.04% day(-1), respectively, n = 6) and lowest in HC. When compared over a similar interval of mass gain, H groups had approximately 25% higher metabolic rates than L, with the highest rates in the HC condition. As a result, fish in the H groups dissipated a greater amount of feed energy as metabolism and, across all groups, there was a direct negative relationship between the quantity of energy dissipated and their SCR. There was no evidence of a neuroendocrine stress response, plasma cortisol was around 1 ng ml(-1) in all conditions. An acute crowding stress increased plasma cortisol to above 120 ng ml(-1) in all groups, but C groups recovered to control levels within 8 h whereas S groups required 20 h. Respirometry on individuals revealed that H fish had approximately 14% higher metabolic rates than L fish, indicating that increased metabolic rate in rearing tanks was in part physiological. The H groups had approximately 15% lower critical swimming speeds than the L groups which, together with their raised metabolic rate, indicated a physiological impairment Thus, high density reduced SGR by raising energy dissipation, at least partially as a physiological response by the fish, although there was no evidence of an endocrine stress response. The only beneficial effect of C was in recovery from acute stress. (C) 2012 Elsevier B.V. All rights reserved.
Mots-Clés: Aerobic scope; charr salvelinus-alpinus; Cortisol; Critical swimming speed; current issues; feeding-behavior; fish welfare; juvenile arctic charr; oncorhynchus-mykiss; respiratory physiology; respirometry; salmon salmo-salar; Stress; stress-response; swimming performance; Welfare indicator
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McKenzie, D. J., Steffensen, J. F., Taylor, E. W., & Abe, A. S. (2012). The contribution of air breathing to aerobic scope and exercise performance in the banded knifefish Gymnotus carapo L. J. Exp. Biol., 215(8), 1323–1330.
Résumé: The contribution of air breathing to aerobic metabolic scope and exercise performance was investigated in a teleost with bimodal respiration, the banded knifefish, submitted to a critical swimming speed (U-crit) protocol at 30 degrees C. Seven individuals (mean +/- s.e.m. mass 89 +/- 7. g, total length 230 +/- 4. mm) achieved a U-crit of 2.1 +/- 1. body. lengths. (BL). s(-1) and an active metabolic rate (AMR) of 350 +/- 21. mg. kg(-1). h(-1), with 38 +/- 6% derived from air breathing. All of the knifefish exhibited a significant increase in air-breathing frequency (f(AB)) with swimming speed. If denied access to air in normoxia, these individuals achieved a U-crit of 2.0 +/- 0.2. BL. s(-1) and an AMR of 368 +/- 24. mg. kg(-1). h(-1) by gill ventilation alone. In normoxia, therefore, the contribution of air breathing to scope and exercise was entirely facultative. In aquatic hypoxia (P-O2=4. kPa) with access to normoxic air, the knifefish achieved a U-crit of 2.0 +/- 0.1. BL. s(-1) and an AMR of 338 +/- 29. mg. kg(-1). h(-1), similar to aquatic normoxia, but with 55 +/- 5% of AMR derived from air breathing. Indeed, f(AB) was higher than in normoxia at all swimming speeds, with a profound exponential increase during exercise. If the knifefish were denied access to air in hypoxia, U-crit declined to 1.2 +/- 0.1. BL. s(-1) and AMR declined to 199 +/- 29. mg. kg(-1). h(-1). Therefore, air breathing allowed the knifefish to avoid limitations to aerobic scope and exercise performance in aquatic hypoxia.
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