Abstract
The reproductive cycle and the energy content of soft parts of Tawera gayi were studied monthly from August 2001 to July 2002 in Ushuaia Bay, Beagle Channel. The degree of sexual maturity was determined histologically. The sex ratio was significantly different of 1:1 (896 females, 796 males, χ2-test, P < 0.05). First sexual maturity occurred at 12 mm shell height in both sexes. In males the reproductive cycle was determined analyzing the monthly percentage of gonadal stages. High percentages (85%–100%) were mature (ripe stage) during a large part of the year (March to September) and in October the 100% of individuals were partially spawned with recovery. An image analyzer was used to determine quantitatively female reproductive cycle. The percentage of gonadal area covered by oocytes was lower in December. The mean number of mature oocytes (diameter >40 μm) by gonadal area and the mean diameter of oocytes reached the lower values during October, November, and December, indicating a spawning peak. This more intensive spawning activity coincides with the phytoplankton bloom in spring. The energy content of soft parts was measured using a microbomb calorimeter in monthly samples during a year. The mean energy content in both sexes was significantly different reaching 20.95 kJ/g AFDW for females and 21.39 kJ/g AFDW for males. The relative condition index attained the lower values in August, September, and October. The monthly values of the energy content did not show significant differences in both sexes. Results of this study indicate that notwithstanding T. gayi lives in a markedly seasonal environment as Subantarctic waters of Beagle Channel shows a protracted gamete production with a principal spawning episode and small pulses of evacuation during the rest of the year.
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