Common snook Centropomus unidecimalis is an important commercial and fishery species in Southern Mexico, however the high exploitation rates have resulted in a strong reduction of its abundances. Since, the information about its population structure is scarce, the objective of the present research was to determine and compare the age structure in four important fishery sites. For this, age and growth of common snook were determined from specimens collected monthly, from July 2006 to March 2008, from two coastal (Barra Bosque and Barra San Pedro) and two riverine (San Pedro and Tres Brazos) commercial fishery sites in Tabasco, Mexico. Age was determined using sectioned saggitae otoliths and data analyzed by von Bertalanffy and Levenberg-Marquardt among others. Estimated ages ranged from 2 to 17 years. Monthly patterns of marginal increment formation and the percentage of otoliths with opaque rings on the outer edge demonstrated that a single annulus was formed each year. The von Bertalanffy parameters were calculated for males and females using linear adjustment and the non-linear method of Levenberg-Marquardt. The von Bertalanffy growth equations were FL t =109.21(1-e-0.21(t+0.57)) for Barra Bosque, FL t =94.56(1-e-0.27(t+0.48)) for Barra San Pedro, FL t =97.15(1-e-0.17(t+1.32)) for San Pedro and FL t =83.77(1-e-0.26(t+0.49)) for Tres Brazos. According to (Hotelling's T 2 , p<0.05) test growth was significantly greater for females than for males. Based on the Chen test, von Bertalanffy growth curves were different among the study sites (RSS, p<0.05). Based on the observed differences in growth parameters among sampling sites (coastal and riverine environments) future research need to be conducted on migration and population genetics, in order to delineate the stock structure of this population and support management programs.

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El robalo blanco (Centropomus undecimalis) es una especie demersal con característica protándrica hermafrodita y hábitos diadrómicos. Se distribuye desde el norte de Florida E.U.A., hasta el sur de Río de Janeiro, Brasil; en el Golfo de México, es abundante en los estados de Tamaulipas, Veracruz y Tabasco. En su área de distribución, el robalo blanco presenta alta importancia comercial y deportiva, esto debido a sus características alimenticias, abundancia, alto valor en el mercado local y regional, así como a la facilidad de obtenerlo por parte de las comunidades pesqueras. En los últimos diez años, el incremento de la demanda en el consumo regional y nacional, así como la modificación de sus hábitats, ha causado que sus niveles de explotación sean altos en el Golfo de México, reduciendo las tallas de captura y la captura por unidad de esfuerzo.

<pre><strong>Background.</strong> In Mexico, the biology of <em>Procambarus</em> has been more studied than other cambarid species due to its diversity and potential use in aquaculture. Fecundity, egg development, and growth under laboratory conditions have been evaluated of the <em>Procambarus</em> (<em>Austrocambarus</em>) <em>llamasi</em>. The effect of density and sex ratio on the development and spawning of gonads and growth of juveniles fed different commercial agricultural and aquaculture feeds has also been studied. There are no records of epibionts infesting this crayfish. The primary objective of this study is to determine the infestation and epibiont identification rates of the Corixidae family and the damage caused to the crayfish.<strong> Methodology.</strong> To determine infestation indexes were calculated: the mean intensity (IM) is the average parasite species in infected organisms (MI = n. Total parasites / n. Infected hosts); abundance (AB) is the average number of parasites per host examined (AB = total number of parasites / n. hosts examined), and prevalence (P) indicates the percentage of organisms parasitized by a species of parasites (P = n .infested hosts / n. hosts examined x 100). <strong>Results.</strong> Of the shrimp analyzed, 76 were infested with 2655 aquatic insect eggs corresponding to 34.93 intensity; 18.18 abundance, and 52.05% prevalence. As far as crayfish sex, infestation occurred in 39% (n=30) of females and 61% (n=46) of males. The aquatic insect in this study belongs to the genus <em>Sigara</em> sp., being the only species registered in the crayfish. <strong>Implications.</strong> When the parasite egg settles near the crab eye region, it is likely to cause visual problems or partial blindness; on the other hand, it could cause a deterioration in the health of the populations of these crabs. <strong>Conclusion.</strong> The eggs located on the cuticular surface of the cephalothorax of <em>Procambarus</em><strong> </strong>(<em>Austrocambarus</em>) <em>llamasi</em> correspond to insect the genus<em> Sigara </em>sp. Half of the studied population of the crayfish is infested by this epibiont. According to the results obtained it was determined that the eggs on the shrimp’s cuticular surface cause cuticle damage due to cementation on its shell.  Eggs can also cause esthetic damage affecting marketing for human consumption and make shrimp overweight due to the egg mass. </pre>