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Yellowfin Mojarra Gerres cinereus (Walbaum, 1792) off the Mexican Pacific coast is a popular low-cost species, which is caught with gill and cast nets. Knowing breeding seasons, gonadal maturity, fecundity and size at sexual maturity is necessary for fishery management. Samples were obtained from April 2010 to November 2011. Size, sex and gonad maturity were recorded, while the gonadosomatic index and the fecundity and condition factors were calculated using the gravimetric method. To calculate this information by age, growth parameters previously published were used. The female:male ratio was 1:1.024. Mature females were observed year round with two major peaks during July and October. Sexual maturation (L 0.5 ) of males and females was 16.40 cm and 20.20 cm, respectively, corresponding to one-year old organisms. First maturity length (L 0.25 ) was 15.80 cm in males and 16.50 cm in females. The hepatosomatic index vs length was LW = 2.00·10 -6 ·TL 4.213 , resulting in a positive allometric relationship. Condition factor indexes increased during February and September. Average oocyte diameter was 0.31 mm (0.15 to 0.45 mm). Fecundity ranged from 37,784 to 1,746,510 oocytes in females from one to seven years of age, and mean relative fecundity was 1332 oocytes·g -1 (294 to 4,430 oocytes·g -1 ). G. cinereus has an early sexual maturity, reproduces once or twice a year and has a high fecundity rate, which allows it to be caught all year round, if caught after the first maturity length.

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Resumen.-La pesca artesanal de la sierra Scomberomorus sierra capturada en la costa de Colima representa el 1% de la captura total. De enero 2003 a marzo 2004 se obtuvieron datos morfométricos de 972 ejemplares y otolitos de 464 especímenes que se utilizaron para analizar edad y crecimiento. Se analizó por dos métodos: análisis de frecuencia de longitud y estudio de otolitos sagittae y asterisci por lecturas directas. Ambos métodos identificaron 5 grupos de edad. Las constantes de crecimiento de la ecuación de von Bertalanffy se determinaron por los métodos Ford-Walford y Gulland y con iteraciones de ajuste, ambas técnicas presentaron un alto coeficiente de determinación, pero tuvo mejor ajuste entre valores observados y calculados, de acuerdo con la suma de cuadrados del error; los resultados fueron: L ∞ = 99,54 cm, K = 0,205, t o = -0,060. La longitud media para cada edad fue: edad 0 (menor a uno) = 1,22 cm, edad 1 = 19,47 cm, edad 2 = 34,33 cm, edad 3 = 46,43 cm, edad 4 = 56,29 cm y edad 5 = 64,32 cm. Se compararon estos resultados con los obtenidos hace 20 años para la misma zona, aplicándose el análisis de curvas coincidentes que mostró una reducción significativa en la longitud promedio de cada edad, que podría deberse a sobreexplotación. S. sierra tiene un L ∞ menor en Manzanillo que en Mazatlán, debido probablemente a las diferencias climáticas, latitudinales o variaciones genéticas de las poblaciones. El índice alométrico de la relación peso-longitud fue isométrico, 3,031 y la longevidad 15 años.Palabras clave: Distribución de frecuencia de longitud, sagittae, asterisci, von Bertalanffy, longevidad Abstract.-The artisanal fishery of sierra Scomberomorus sierra along the coast of Colima represents 1% of the total catch. From January 2003 to March 2004 morphometric data of 972 organisms and otoliths of 464 specimens were obtained to determine age and growth. Growth study was carried out by two methods: length frequency analysis and study of sagittae and asterisci otoliths. Both methods identified 5 age groups. Growth parameters of von Bertalanffy's equation were determined by Ford-Walford and Gulland methods and an iteration adjustment, both techniques showed a high determination coefficient, but the second was better between observed and calculated values according to the sum of squared error; the results obtained were: L ∞ = 99.54 cm, K = 0.205, t o = -0.060. Mean size for each age was: age 0 (less than one) = 1.22 cm, age 1 = 19.47 cm, age 2 = 34.33 cm, age 3 = 46.43 cm, age 4 = 56.29 cm and age 5 = 64.32 cm. Comparisons for this species were made with results from 20 years ago in the same area, using coincident curves test, showing a significant reduction in average length of each age; this may be caused by changes in the fishery or overexploitation, although growth parameters show the opposite trend. S. sierra has a lower L ∞ in Manzanillo than in Mazatlan, which could be explained by climatic, latitudinal differences or due to population's genetic variations. The allometric index from the weight-len...

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