INFLUENCE OF TEMPERATURE AND DIET ON THE POSTPRANDIAL INCREASE OF THE METABOLIC RATE OF HARPAGIFER BISPINIS

F. A. VANELLA; J. CALVO

Berichte zur Polar- und Meeresforschung / Reports on Polar and Marine Research. Extended Abstract of the IBMANT / ANDEEP International Symposium & Workshop

Alfred-Wegener-Institut

Lugar: Bremerhaven; Año: 2005 vol. 507 p. 185 - 186

1618-3193

Activity patterns, specific ecological habits and environmental temperature determine the metabolic rate of poikilotherms.  Subantarctic fish such as Harpagifer bispinis are subject to wide variations in temperature and daylight hours throughout the year and would be expected to exhibit changes in their activity patterns. This study analyses the influence of temperature on Gastric Evacuation Time (GET) and the increase of the metabolic rate after a feed in this species. Specimens of Harpagifer bispinis (mean total length: 76.9 ± 8.5 mm; mean body mass: 6.1 ± 1.6 g) captured in the area of Ushuaia bay were kept in individual plastic containers submerged in a controlled temperature tank. The fish were distributed in two groups fed with amphipods and isopods respectively. The caloric content, water content and ash content of amphipods and isopods, similar to those used as food was determined. Oxygen consumption was determined using a Clark -type polarographic oximeter cell.  After ten days of acclimatisation at 10ºC, when the fish showed stable oxygen consumption, interpreted as routine consumption (VO2R), they were fed and oxygen consumption was determined periodically until routine levels were reached. The temperature of the aquariums was then lowered at a rate of 1ºC per day to reach 4ºC when VO2R was measured once more.  Once the values stabilised the fish were fed and oxygen consumption levels were measured again.  This procedure was repeated at 2ºC.  In other fish gastric evacuation time (GET) was determined for each diet (amphipods and isopods), following the same acclimation program as that used for the oxygen consumption experiment. After feeding the fish at each experimental temperature, the oxygen consumption (VO2M) increase doubled the resting values (VO2R). After feeding with isopods the specific dynamic action (SDA) remained high for 81-178 hours, when amphipods were used, the levels remained high for 64-79 hours.  Sham feeding procedures maintained routine metabolic rates. Gastric evacuation time (GET) for Harpagifer bispinis was significantly shorter at higher temperatures, lasting approximately 4 days for both food items at 10ºC.  At 2 and 4ºC the GET lengthened to approximately 8 days in fish fed amphipods and 12-14 days in fish fed isopods. Feeding produced an increase in oxygen consumption at all experimental temperatures with both food items for this species.  However, at lower experimental temperatures the proportion of energy used (SDA coefficient = (Energy equivalent SDA (kJ) / Energy ingested (kJ)) x 100) for both food items fell. SDA Energy values and SDA Time were lower in fish fed amphipods as compared to those fed isopods.  This could be due to the higher content of ash and the lower energetic content of the latter.  The VO2R of H. bispinis was lower than other Antarctic notothenioids with similar lifestyles.