Resumen de Primeros datos sobre el crecimiento en la Ecdisis y pruebas de sistemas de marcado de la Nécora, "Macropipus Puber" (L.) (Decapodabrachyura), en el laboratorio: N.º 300
Preliminary studies on increase in size at ecdysis and tagging experiments on the velvet swimming crab Macropipus puber(L.) (DecapodaBrachyura), in the laboratory.
The growth increments at ecdysis and the prediction of succesive instars as well as the efficiency of some tagging methods have been studied in this paper.
There was a percent increase in the ecdysis number with succesive experiments, according to the increase of water temperature. The percentage of crabs that moulted in the laboratory ranged from 11 to 29 % , generally during the first days of the experiment.
The period of ecdysis ranged from a few minutes to several hours, and the process usually occurred at night: 85 to 100 % of the increase in size was due to absorption of water at ecdysis and up to one hour after it. The duration of the two first post-ecdysis periods ranged from 3 to 18 days, increasing at lower temperatures and with the size of the crabs.
The average increments at ecdysis were obtained for 88 crabs; pre-ecdysis size range 14.5 to 70 mm carapace width.
An analysis of covariance was performed on the regression lines (pre-ecdysis caparace width against post-ecdysis caparace width), corresponding to sex, to crabs with cheliped tags that increase in size in the first ten days of being in the laboratory and those that increase in size after ten days. All pairs of lines were found to be significantly different in residual variances, slopes, and/or intercepts. The time in the laboratory reduces the increment in size at ecdysis by between 0.5 and 4.5 %, depending on the size and/or sex. Growth increments per molt (of the crabs that increase in size in the first ten days in the laboratory) varied from 31.03 to 13.95 % (X̅ = 20.35 %; S X̅ = 1.13) for the males, and for the females between 31.39 to 10.90 % (X̅ = 18.51; S X̅ = 0.79), decreasing with size.
The growth at ecdysis in similar in both sexes below 45 or 55 mm carapace width, when they attain maturity. The pre-ecdysis: post-ecdysis relationship changes with the onset of sexual maturity; subsequently the growth was significantly less in females than in males. The prediction of the instars is more precise using two regression lines for every sex (Table II).
The tagging mortality was greater among suture and toggle tagged than among claw tagged crabs; the mortality estimated by the “suture tag” was 8 %, and for the “toggle tag” ranged 17 to 27 %. Maximum values of tag retention during ecdysis was 33 % for the “suture tag” and 0 % for the “toggle tag”. The loss of tags during the intermolt was 16 % for the suture tagged and 19 % for the toggle tagged crabs. There were no significant differences in a “t” test between the increment in size at ecdysis using these two tagging systems and the claw tagged crabs.
