Estudio de edad y crecimiento del besugo Pagrus pagrus del sector costero bonaerense
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The samples analyzed for growth parameters determination both in length and weight of the red porgy Pagrus pagrus corresponded to the years 1972 up to 1981 and to two areas of the Buenos Aires (Argentina)coastal shelf: a northern one (35°-36°S)and a southern one (39°-40°). Through age determination, based on the countdown of rings in scales, the parameters of the von Bertalanffy growth equation for the two mentioned areas were estimated as follows: 1)northern area:Lý=44.7;k=0.154;to=-2.96, and 2)southern area:Lý=49.9;k=0.153;to=-2.81. The results shown that the infinite length of the red porgy from the southern area was the greatest. The maximum likelihood method permitted to calculate, for each region,the three parameters and the respective confidence intervals, with a95. probability. The comparison of those values demostrated statistically significant differences among areas. Growth in length was similar in both sexes. The instantaneous rate of natural mortality for the northern area was estimated to be 0.182. The values of total radios (R)and those corresponding to each ring(rdn)of scales of specimens from the southern area were higher than those observed from the north. This difference was more evident at the level of the first mark in the scale, and the same was seen when the marginal scale increase at the 1+ in both regions were compared.Those differences bring us to think that northern and southern specimens came from two different groups. From the comparativ estudies on the length/weight relationship the following inferences. were done: 1)There were meaningful differences during a large part of the year, indicating that males appeared to be healthier; 2)Eventhough a great variability of this relationship was observed both among successive months within an annual cycle, as well as amongyears, it can be said that growth in weigth decreased gradually from September to January, what is supposed to be linked to reproductive events. From January to April the power of the equation increased, reaching a maximum during April, as a result of a better nourishment in late summer, after spawning and 3)The comparison by regions showed that April and September did not show statistically significant differences, neither for females nor for males and that in October, differences between parameters for females from the two areas were observed, but not among males, probably due to an earlier gonadal maturity of the northern females. The differences which were observed in growth of red porgy, from both areas, can be due to better conditions within the southern area, either of an ecological nature (environmental and/or nourishment)or resulting from a lighterfishing effort. The above mentioned results compel us to recommended the independent monitoring of both groups.