Comparative age and growth of common snook Centropomus undecimalis (Pisces: Centropomidae) from coastal and riverine areas in Southern Mexico

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 FLt=109.21(1-e-0.21(t+0.57)) for Barra Bosque, FLt=94.56(1-e-0.27(t+0.48)) for Barra San Pedro, FLt=97.15(1-e-0.17(t+1.32)) for San Pedro and FLt=83.77(1-e-0.26(t+0.49)) for Tres Brazos. According to (Hotelling’s T², 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.

El robalo blanco Centropomus undecimalis representa un ingreso monetario significativo y un recurso alimentario para todas las comunidades rurales cercanas a su distribución. Se determinó la edad y crecimiento de esta especie. Los organismos se recolectaron mensualmente en los desembarcos de la pesca artesanal de las cooperativas de mayor contribución en la zona costera (Barra Bosque y San Pedro) y ribereña (San Pedro y Tres Brazos) entre julio 2006 y marzo 2008. La edad se determinó mediante otolitos seccionados. La edad estimada fue de 2 a 17 años. Mensualmente se estableció la formación anillos opacos y traslúcidos. Para ambas zonas de estudio agrupadas, se validó el retrocálculo por comparación de tres métodos (Fraser-Lee, Dahl-Lea y Whitney-Carlander), se encontraron diferencias significativas (ANCOVA, p<0.05) entre el promedio de la longitud observada y la longitud retrocalculada. Las constantes de la ecuación de von Bertalanffy fueron calculadas para cada sexo y combinados, se empleó el método no lineal de Levenberg-Marquardt’s. La edad estimada para el robalo blanco fue de 2 a 17 años. Se encontraron diferencias significativas en el crecimiento entre sexos (T² Hotelling, p<0.05). Los parámetros de crecimiento para ambos sexos fueron, zona costera: Barra Bosque Lf t=109.21(1-e-0.21(t+0.57)), Barra San Pedro Lf t=94.56(1-e-0.27(t+0.48)), y para la zona ribereña: San Pedro Lf t=97.15(1-e-0.17(t+1.32)) y Tres Brazos Lf t=83.77(1- e-0.26(t+0.49)). Se encontraron diferencias significativas en las curvas de crecimiento de von Bertalanffy entre las poblaciones comparadas (RSS, p<0.05).

Embryonic development of aplodinotus grunniens (perciforme: sciaenidae) in Tenosique, Tabasco, Mexico / Desarrollo embrionario de Aplodinotus grunniens (perciforme: sciaenidae) en Tenosique, Tabasco, México

The description of the embryonic and larval development was based on 30 eggs and 30 larvae. Breeders were collected on the Usumacinta River, Tabasco, Mexico and were subjected to manual fertilization in May 2011. Fertilized eggs were spherical, pelagic, translucent and non-adhesive and had an average diameter of 1.07 mm (SD = 0.10), showing a concentric lipid droplet of 0.85 mm (SD = 0.02). The embryo occupied 100 percent of the perivitelline space at hour 14:08 post-fertilization and the egg measured 1.18 mm (SD = 0.14) at this stage. Eclosion started 17 hours post-fertilization when larvae had a length of 2.54 mm (SD = 0.66). Eight preanal and 13 postanal myomeres were observed exhibiting a light brown color. The morphologic characters recorded in this study are similar to the anatomy of embryos and larvae of the Sciaenidae family. The diameter of the eggs and the length of the larvae for A. grunniens are slightly larger than other Sciaenidae species: A. regius, C. striatus, B. chrysora, C. regalis, L. xanthurus, P. cromis, G. lineatus and S. ocellatus. This is the first study of its kind and its results contribute to the knowledge of the species reproductive biology.

La descripción del desarrollo embrionario y larval se basó en 30 huevos y larvas 30. Los reproductores se recolectaron en el río Usumacinta, Tabasco, México, y se sometieron a la fertilización manual en mayo de 2011. Los huevos fertilizados fueron esféricos, pelágicos, translúcido y no adhesivos presentaron un diámetro promedio de 1.07mm (SD = 0,10), mostrando una gota lipidica concéntrica de 0,85 mm (SD = 0,02). El embrión ocupo el 100 por ciento del espacio perivitelino a las 14:08 horas después de la fertilización y el huevo midió 1,18 mm (SD = 0,14) en esta etapa. La eclosión comenzó a las 17 horas después de la postfertilización, las larvas presentaron una longitud promedio de 2,54 mm (SD = 0,66). Se observaron ocho miómeros preanal y 13 postanal exhibieron una coloración marrón. Los caracteres morfológicos registrados en este estudio son similares a la anatomía de los embriones y larvas de la familia Sciaenidae. El diámetro de los huevos y la longitud de las larvas de A. grunniens son ligeramente más grandes que otras especies de Sciaenidae: A. regius, C. striatus, B. chrysora, C. regalis, L. xanthurus, P. cromis, G. lineatus y S. ocellatus. Este es el primer estudio de su tipo y sus resultados contribuyen al conocimiento de la biología reproductiva de la especie.

Reproductive biology of common snook Centropomus undecimalis (Perciformes: Centropomidae) in two tropical habitats

In Southeastern Mexico, Centropomus undecimalis is an important fish species of sport and commercial fisheries for coastal and riverine communities. Fisheries along rivers and coasts depend on migratory habits of this species, and these movements are probably related to reproduction. In spite of its economic importance, few studies have been conducted focusing on its reproductive biology, and this research aims to analyze these habits. Samples (fork length, somatic and gonads weight, and macroscopic maturity stages) were obtained from organisms collected by fishermen from the largest fishing cooperatives along the coastal and riverine areas of Tabasco, from July 2006 to March 2008. Fish size ranged from 34 to 112cm fork length, with an average age of 6.42 years for males and 9.12 years for females. In riverine areas, fish sizes ranged from 30 to 85cm and the average age was 5.5 years for males and 6.6 years for females. Significant differences were recorded between lengths of males and females from the two areas (Kruskal-Wallis, p<0.05). The male:female ratio was 1:0.68 in the coast, and 1:0.16 in riverine areas. The length-weight relationship did not vary between both sexes among areas (ANCOVA, p>0.05). A curve for eviscerated weight was calculated for both sexes, for coastal fishes SW=0.0059(FL) 3.07, and the riverine ones SW=0.0086(FL) 2.98, with an isometric growth (b=3). The period of maximum reproduction was from July to August, with temperatures of 28 to 30°C. A significant correlation between the gonadosomatic index (GSI) and rainfall was recorded for samples of both males and females from coastal areas (r=0.63, r=0.70) whereas only one positive correlation was recorded for riverine females (r=0.57). The size at first maturity (L50) was estimated at 60cm and 80cm (FL), corresponding to 5.5 and 8.5 years of age, for males and females, respectively. An important proportion of mature females of eight years and older, suggests that these ages contribute significantly to the reproductive biomass. The results indicate that due to changes in the exploitation period, we recommend to protect populations of the common snook. Rev. Biol. Trop. 59 (2): 669-681. Epub 2011 June 01.

En este estudio, se analizó la biología reproductiva y poblacional del robalo blanco (Centropomus undecimalis). El material biológico se obtuvo en los desembarcos de la pesca artesanal de las cooperativas de mayor contribución en la zona costera y ribereña durante julio de 2006 a marzo de 2008. En la zona costera las tallas oscilaron entre 34 a 112cm (LF) y en la zona ribereña entre 30 a 85cm. Se encontraron diferencias significativas entre las longitudes de machos y hembras en ambas zonas de estudio (Kruskal-Wallis, p<0.05). La proporción machos:hembras fue 1:0.68 en la costa y 1:0.16 para la zona ribereña. La relación longitud-peso no difirió entre sexos en las dos zonas de estudio (ANCOVA, p>0.05). El periodo máximo reproductivo fue de julio a agosto. En la zona costera, se encontró una correlación significativa entre el iGS y precipitación pluvial para machos y hembras (r=0.63, r=0.70), en la zona ribereña solo se encontró un correlación positiva en las hembras (r=0.57). La talla de primera madurez (L50) se estimó a los 60cm para hembras y 80cm (LF) para machos correspondiendo a 5.5 y 8.5 años de edad respectivamente. Los resultados sugieren un cambio en el periodo de explotación para la conservación de las poblaciones del robalo blanco y su producción.

Aquatic food webs in mangrove and seagrass habitats of Centla Wetland, a Biosphere Reserve in Southeastern Mexico

Mangrove and seagrass habitats are important components of tropical coastal zones worldwide, and are conspicuous habitats of Centla Wetland Biosphere Reserve (CWBR) in Tabasco, Mexico. In this study, we examine food webs in mangrove- and seagrass-dominated habitats of CWBR using stable isotope ratios of carbon and nitrogen. Our objective was to identify the importance of carbon derived from mangroves and seagrasses to secondary production of aquatic consumers in this poorly studied conservation area. Carbon and nitrogen isotope ratios of basal sources and aquatic consumers indicated that the species-rich food webs of both habitats are dependent on riparian production sources. The abundant Red mangrove Rhizophora mangle appears to be a primary source of carbon for the mangrove creek food web. Even though dense seagrass beds were ubiquitous, most consumers in the lagoon food web appeared to rely on carbon derived from riparian vegetation (e.g. Phragmites australis). The introduced Amazon sailfin catfish Pterygoplichthys pardalis had isotope signatures overlapping with native species (including high-value fisheries species), suggesting potential competition for resources. Future research should examine the role played by terrestrial insects in linking riparian and aquatic food webs, and impacts of the expanding P. pardalis population on ecosystem function and fisheries in CWBR. Our findings can be used as a baseline to reinforce the conservation and management of this important reserve in the face of diverse external and internal human impacts.

Manguezais e pradarias de gramíneas são importantes componentes das zonas costeiras tropicais em todo o mundo, sendo habitats comuns nos ''Pântanos de Centla'', uma Reserva da Biosfera localizada em Tabasco, México. Nesse trabalho, são investigadas as teias alimentares de habitats dominados por manguezais e pradarias de gramíneas, através de isótopos estáveis de carbono e nitrogênio, tendo como objetivo identificar a importância do carbono derivado desses produtores para a produção aquática secundária nessa unidade de conservação tão pouco estudada. As razões isotópicas de carbono e nitrogênio das fontes basais e dos consumidores aquáticos indicam que as teias alimentares, ricas em espécies, de ambos os habitats, são dependentes da produção ripária. O abundante mangue-vermelho Rhizophora mangle parece ser a fonte primária de carbono no habitat dominado por manguezais. Em contraste, muito embora as pradarias de gramíneas sejam conspícuas no ambiente lagunar estudado, muitos dos consumidores da teia alimentar nessa região parecem depender do carbono oriundo da vegetação ripária (e.g. Phragmites australis).A espécie de bagre exótica Pterygoplichthys pardalis possui assinaturas isotópicas que se sobrepõem a das espécies nativas (incluindo algumas de elevado valor comercial na pesca), sugerindo competição potencial por recursos. Novas investigações deveriam avaliar o papel dos insetos terrestres como elo de conexão entre as teias alimentares da mata ripária e do ambiente aquático, bem como os impactos da expansão da população de P. pardalis sobre o funcionamento do ecossistema e das pescarias no ''Pântano de Centla''. Considerando os múltiplos impactos antrópicos na região, os resultados obtidos no presente trabalho podem ser utilizados como uma base de referência em programas de gerenciamento e conservação da diversidade nessa importante Reserva da Biosfera.