The instantaneous mortality coefficient (F + M) of the commercial weakfish, Macrodon ancylodon (Bloch, 1801) caught by trawls along southern Brazilian coast (from latitude 28ºS to 34ºS), was computed by means of the annual catch variation (in number) by age per fishing effort from March 1961 to December 1964. The instantaneous mortality coefficient mean values for female and male was respectivelly 1.31 and 1.53. One year old recruits appear in the landings and the mesh selectivity operates on fish up to three years old. Three-year old class predominates in the landings.

This paper aims at the determination of (1) period and area of spawning, (2) length and age at first spawning and (3) sex ratio of the 'pescada-foguete' (Macrodon ancylodon) from the southern coast of Brazil. The results obtained show that spawning occurs during October-May with a partial spawning in December and in March-April; the area of spawning was found to be between latitude 32ºS and longitude 51ºW and 52ºW. The first maturation occurs when the fish reach 25 cm long, being complete in about six months. The sex ratio found was 48% females for 52% males.

We determined the age of the commercial marine fish "pescada-foguete" (Macrodon ancylodon, Bloch 1801) caught by trawls along the southern coast of Brazil (28ºS-34ºS), from 1961 to 1963, by means of the annuli in otoliths (CHUGUNOVA, 1959). We correlated the mean total length (L) in centimetres with the age (t) in years by means of the BERTALANFFY expression adjusted by FORD-WALFORD method (BEVERTON & HOLT, 1957). The mean total length was correlated with the mean weight (W) in grams, by means of the expression W = aLb adjusted by least square method, after a logarithmic transformation. Results:

The "pescada-foguete" fish presented (1961-1964) migration along the southern coast of Brazil (from 28ºS to 34ºS), according to the following expression, adjusted by the least squares method: y = 30.2 + 1.7 cos 30 (x - 1.5) where: y - latitude with maximum production per unit effort (ºS) X = 1, % .... 12, months of the year

In this paper data on catch and effort by gear are analysed, for weakfish (Macrodon ancylodon) landed at Santos from January 1959 to December 1963. The region studied was a narrow band about 30 nautical miles wide, along the southern coast of Brazil, between 23º S and 34º S. From the analysis of monthly data of production per unit-effort by squares of 1º on a side, we divided the studied region in two areas: area I (from 23º S to 27º S) and area II (from 28º S to 34º S). The index of unit-effort production and the effort concentration index were computed grouping the data by quarters. From the results we may drow the following conclusions: 1 - In a general way, the effort for catch weak-fish has been applied satisfactorily because the medium and large parejas have operated almost in areas with average density on¹ higher than average density; 2 - The production per unit-effort in the area I is smaller than the production in area II, which suggests that the index of abundance is higher in area II; 3 - The decrease in production per unit-effort, in area II, suggests a decrease in the abundance or availability of weak-fish in this area; 4 - In the area I, the index of production per unit-effort remained approximately at the same level.