ABSTRACT
Menidia humboldtiana, a native species of Mexico, is a common inhabitant of local reservoirs. It represents a highly appreciated fish of economic importance in the central part of the country because of its delicate flavor. Trophic behavior of this species is important to understand the relationships with other fish species in reservoirs. With the aim to study this specific topic, the trophic spectrum, selectivity coefficient and overlap, were determined among different sizes of the Silverside M. humboldtiana. For this, both zooplankton and fish samples were taken during four different seasons of 1995. Zooplankton samples were taken through a mesh (125micron), and all organisms were identified to generic level. Fish were captured and grouped into standard length intervals per season, and the stomach contents were obtained and analyzed. Trophic interactions included the stomach contents analysis (Laevastu method), the coefficient of selection (Chesson) and the trophic overlap (Morisita index modified by Horn) between sizes. A total of 14 zooplankton genera were identified, of which Bosmina was the most abundant (29 625 ind./10L) followed by Cyclops (9 496 ind./10L), during the spring. Small size fishes (1-4.9cm) consumed high percentages of Cyclops in the spring (61.24%) and winter (69.82%). Ceriodaphnia was consumed by fish sizes of 3-10.9cm (72.41%) and 13-14.9cm (95.5%) during the summer; while in autumn, small sizes (1-4.9cm) ingested Mastigodiaptomus and Ceriodaphnia; Daphnia and Bosmina were consumed by fishes of 5-8.9cm and the biggest sizes (9-14.9cm) feed on Ceriodaphnia. M. humboldtiana makes a selective predation by the genera Ceriodaphnia, Daphnia, Mastigodiaptomus, Bosmina and Cyclops, depending on the size length interval. The trophic overlap was very marked among all sizes on spring, autumn and winter, unlike in summer fish of 1-2.9 and 11-12.9cm did not show overlap with other length intervals. M. humboldtiana is a zooplanktivore species, which performs a selective predation and a marked trophic overlap between the different fish sizes.
Menidia humboldtiana es una especie nativa muy apreciada por su delicado sabor. Se determinó el espectro trófico, selectividad y solapamiento trófico de ésta, durante 1995 (épocas del año), se obtuvieron muestras de zooplancton e identificaron a nivel genérico. Los peces capturados se agruparon en intervalos de longitud estándar para cada época. Se analizaron los contenidos estomacales (método volumétrico, Laevastu), selectividad (Chesson) y solapamiento trófico (Morisita). Se registraron 14 géneros de zooplancton; Bosmina el más abundante (29 625ind/10L) seguido por Cyclops (9 496ind/10L) ambos en primavera. Los peces pequeños (1-4.9cm) consumen a Cyclops en altos porcentajes en primavera e invierno, 61.24-69.82% respectivamente. Ceriodaphnia es consumida por peces de 3-10.9cm y de 13-14.9cm con 72.41-95.5% en verano; en otoño las tallas pequeñas ingieren a Mastigodiaptomus y Ceriodaphnia; Daphnia y Bosmina por peces de 5-8.9cm y los más grandes (9-14.9cm) a Ceriodaphnia. M. humboldtiana realiza una depredación selectiva por Ceriodaphnia, Daphnia, Mastigodiaptomus, Bosmina y Cyclops. El solapamiento trófico fue muy marcado entre todas las tallas en primavera, otoño e invierno, a diferencia en verano los peces de 1-2.9 y 11-12.9cm no registraron un solapamiento con otros intervalos de longitud. M. humboldtiana es una especie zooplanctófaga, que realiza una depredación selectiva y un marcado solapamiento trófico entre los intervalos de longitud.
Subject(s)
Animals , Food Chain , Feeding Behavior/physiology , Fishes/physiology , Body Size , Fishes/anatomy & histology , Fishes/classification , Gastrointestinal Contents , Mexico , SeasonsABSTRACT
Selectivity of zooplankton and trophic overlap between size Menidia humboldtiana fish (Atheriniformes: Atherinopsidae) in the reservoir Danxhó, Mexico. The Menidia humboldtiana silverside is considered one of the most important species in fisheries in some states of Mexico. Knowing the choice that this species exercises over its food gives us an understanding of the behavior of zooplankton in presence of zooplanktonic fish, and tells us if the silverside choose amongst bigger prey fish, and if there is competition for food between the native and introduced fish in the reservoir. The purpose of this study was to determine if M. humboldtiana selects its food, and in which genera, and to establish whether there was an overlap in the diet of the different sizes of silverside. The fish were catched with a 88 mm mesh net, in six sampling points during one year, from Danxhó (19°5´17" - 53´46" N, 99° 32´42" - 35´40" W) reservoir. Samples of filtered zooplankton were also taken with a 125 micron net. The analysis of stomach contents was carried out in fish grouped by regular size intervals during each season of the year, using the volumetric method and Chessons selectivity coefficient. To evaluate the trophic overlap between the different size groups, the Morisita index, modified by Horn, was used. The zooplankton community was represented by twelve genera: Mastigodiaptomus and Cyclops (Copepoda); Bosmina, Diaphanosoma, Daphnia, Ceriodaphnia, Moina, Alonopsis and Camptocercus, (Cladocera); Asplanchna, Conochillus and Filinia (Rotifera). Mastigodiaptomus was the most abundant throughout the year. The silverside consumed only four genera: Bosmina, Mastigodiaptomus, Daphnia and Ceriodaphnia; the group measuring 5 to 8.9 cm consumed a high percentage of Bosmina, Mastigodiaptomus and Daphnia, and a lesser percentage of Ceriodaphnia. The larger fish (9 to 10.9 cm) consumed only Mastigodiaptomus and Daphnia. In accordance with the selectivity values, the small and medium size silverside selected their prey, with more intensity on the genera Bosmina and Daphnia, while the bigger fish concentrated on Daphnia and Mastigodiaptomus. During spring, the silverside between 3 to 8.9 cm showed overlap in diet; in summer the bigger size group (7-10.9 cm) showed the overlap. In autumm the overlap ocurred in all sizes, and in winter it was shown only in the medium size fish (5-8.9 cm). Rev. Biol. Trop. 57 (1-2): 187-194. Epub 2009 June 30.
El charal Menidia humboldtiana es considerado como una de las especies de gran importancia en la industria pesquera de algunos estados de México. Es necesario conocer el efecto que esta especie ejerce sobre su alimento para saber si seleccionan las presas de mayor talla, si hay competencia por el alimento entre especies nativas e introducidas, y para comprender el comportamiento del zooplancton ante peces zooplanctófagos. Se determinó si M. humboldtiana selecciona su alimento, sobre qué géneros lo hace, y si existe traslape en la dieta entre las diferentes tallas. Los peces se recolectaron por medio de un chinchorro de 88 mm de abertura de malla, en seis estaciones de muestreo durante un año, en el embalse Danxhó, y una muestra de zooplancton fue recolectada por filtrado con una red de 125 µm. El análisis de los contenidos estomacales se realizó en peces agrupados en intervalos de longitud estándar para cada época del año, por medio del método volumétrico. Para evaluar el traslape trófico entre los diferentes intervalos de longitud, se utilizó el índice de Morisita modificado por Horn. El zooplancton estuvo representado por doce géneros: Mastigodiaptomus y Cyclops (Copepoda); Bosmina, Diaphanosoma, Daphnia, Ceriodaphnia, Moina, Alonopsis y Camptocercus (Cladocera); Asplanchna, Conochillus y Filinia (Rotifera). Durante la primavera, los charales de 3-8.9 cm presentaron un marcado traslape, para el verano fueron los grandes (7-10.9 cm), en otoño el traslape fue en todas las tallas, y en invierno solo las tallas intermedias (5-8.9 cm) lo presentaron.
Subject(s)
Animals , Feeding Behavior/physiology , Fishes/physiology , Predatory Behavior/physiology , Zooplankton/classification , Fishes/classification , Gastrointestinal Contents , Mexico , SeasonsABSTRACT
Objetivo. Estudiar el ciclo sexual y la fecundidad del pejerrey patagónico, especie de alto valor comercial y deportivo, en el embalse Ezequiel Ramos Mexía (Neuquén, Río Negro; Argentina). Materiales y métodos. Se colectaron 9307 ejemplares. El ciclo sexual se estudió mediante la observación macroscópica de las gónadas y la fecundidad absoluta se calculó con la técnica volumétrica. Resultados. La talla de primera madurez sexual (Lm 50%) se estimó a través del ajuste de una curva logística. El desove tuvo lugar en primavera y principios de verano (septiembre a diciembre). La talla de primera madurez sexual, en las hembras, fue de 244,37 mm (Lt). La fecundidad absoluta varió entre 3.976 ovocitos en una hembra de 296 mm (Lt) y 190 g y 20.879 ovocitos en una hembra de 420 mm (Lt) y 704 g. Conclusiones. No se observó una relación significativa entre la fecundidad relativa y la longitud total de los ejemplares. La proporción de sexos resultó equilibrada en las clases de longitud intermedias, pero mostró una preponderancia de hembras en las mayores. El ciclo ovárico es altamente estacional y coincide con el de poblaciones de la especie en otros ambientes patagónicos. La fecundidad, en cambio, resultó más elevada que la observada en el lago Moreno, situado en la región cordillerana.
Objective. To study the sexual cycle and fecundity of the Patagonian silverside, a species of high commercial and sport value, from Ezequiel Ramos Mexia reservoir (Neuquen, Rio Negro; Argentina ). Materials and methods. Sampling was conducted between 1982 and 1986, and 9307 specimens were collected. The sexual cycle was studied by macroscopic observation of the gonads and fecundity was assessed using the volumetric method. Results. Length at first maturity (Lm 50%) was estimated by fitting a logistic curve. Spawning took place in spring and early summer (September to December). Length at first maturity was 244.37 mm (Lt) in females. Absolute fecundity ranged between 3.976 oocytes in a 296 mm (Lt), 190 g female and 20.879 oocytes in a 420 mm (Lt), 704 g female. Conclusions. No significant relation was found between relative fecundity and total length. The sex ratio was approximately 1:1 at intermediate length classes, but females predominated in the larger classes. The ovarian cycle was highly seasonal and coincided with that of populations from other Patagonian environments. Fecundity, on the other hand, was higher than that observed at Moreno Lake, in the Andean region.
Subject(s)
Fertility , Argentina , ReproductionABSTRACT
Atherinella blackburni is a silverside species whose occurrence on the Brazilian coast was not properly registered until recently. So far, records of its distribution along the Brazilian shore were limited to Itaparica Island, Bahia State, and Porto Inhaúma, Rio de Janeiro State. In a recent survey of the ichthyofauna of Itamambuca Beach, Ubatuba, São Paulo State, 100 specimens of this species were collected, yielding a considerable source of information regarding its ecology and a new southern limit of its distribution. A detailed survey of an ichthyological collection revealed lots of this species from regions of the Brazilian Northeast, resulting in a northward expansion of the occurrence of A. blackburni in Brazilian waters. Besides the populations found on the Brazilian coast, the species also occurs discontinuously in the Atlantic coasts of Costa Rica, Panama and Venezuela. Meristic and morphometric analysis showed overlapped values between Brazilian populations and the ones closer to the Caribbean. An ecological study of A. blackburni at Itamambuca Beach revealed that it is a predominantly diurnal species with preference for warm and salty waters, often occurring in sandy-bottom environments. It was more abundant in Summer and Winter, when individuals with smaller values of length and weight also occurred.
Atherinella blackburni é uma espécie de peixe-rei cuja ocorrência na costa brasileira não havia sido precisamente registrada até recentemente. Ainda assim, sua distribuição no litoral brasileiro estava restrita à Ilha de Itaparica, Bahia e Porto Inhaúma, Rio de Janeiro. Em um recente levantamento da ictiofauna da Praia de Itamambuca, Ubatuba, São Paulo, foram coletados 100 espécimes desta espécie, originando uma fonte considerável de informações no tocante à sua ecologia e a um novo limite sul de sua distribuição. Um estudo detalhado revelou lotes desta espécie em regiões do nordeste brasileiro em coleção ictiológica, resultando na expansão para o norte da ocorrência de A. blackburni em águas brasileiras. Além das populações encontradas na costa brasileira, a espécie também ocorre descontinuamente na costa Atlântica da Costa Rica, Panamá e Venezuela. Análise merística e morfométrica revelou valores sobrepostos entre populações brasileiras e aquelas mais próximas ao Caribe. O estudo ecológico de A. blackburni na Praia de Itamambuca evidenciou que é uma espécie predominantemente diurna com preferência por águas quentes e salgadas, freqüente em ambientes com fundo arenoso. Foi mais abundante no verão e inverno, quando indivíduos com menores valores de comprimento e peso também ocorreram.
Subject(s)
Animals , Ecosystem , Fishes/classification , Brazil , Fishes/anatomy & histology , Fishes/physiology , Population Dynamics , Seasons , SeawaterABSTRACT
The first reproductive cycle of 50 females of the shortfin silverside, Chirostoma humboldtianum (Valenciennes) in culture conditions was analyzed. Ovarian developmental stages, gonadosomatic (GI) and hepatosomatic (HI) indexes were described. Histo-logical description of the ovaries and quantification of estradiol serum levels (E2) and 17α-hydroxy-4-pregnen-3-one (17-P4) by radioinmune assay were performed. Results showed a first reproductive season longer than six months. Females initiated spawning at the age of one year. Four ovarian maturation stages (I to IV) were determined during the spawning season and one (V) during the non-spawning season, the last one showed a non-defined pattern of development. The GI and HI indexes values indicate a positive lineal relation to body-weight only during the reproductive season (r² = 0.74 and r² = 0.86, P < 0.05, respectively). Histological analysis of the ovaries indicated that the species correspond to the pattern described as group-synchronous with multiple spawnings. The follicular population showed reproductive activity during the first stages of maturation with a predominant population of pre-vitellogenic follicles. As the ovarian maturation increased, the presence of all the follicular developmental stages was observed, with a tendency of an increase of vitellogenic and mature follicles. The concentration of circulating sexual steroid hormones of estradiol (E2) and 17α-hydroxy-4-pregnen-3-one (17-P4) were high during stage I (2.5 ± 0.7 ng/m L and 2.4 ± 0.3 ng/mLfor E2 and 17-P4, respectively); a decrease was observed during stage II, and the highest values were observed in stage IV (7.6 ± 2.1 ng/mL for E2 and 1.8 ± 0.9 ng/mL for 17-P4). The same pattern was observed during non-spawning season (ANOVA P < 0.05), these results are the first findings on the reproductive physiology of the shortfin silverside fish, suggesting an early steroidogenic activity in immature females. Furthermore, the species maintains its hormonal capacity during the post-spawning season, as it is supported by their follicular composition. The aforementioned will allow to have a better understanding of the mechanisms involved in their reproductive processes and to improve the mechanisms utilized to control their reproduction and for the production of eggs and larvae in culture conditions.
Se analizó el primer ciclo reproductivo de 50 hembras de pez blanco, Chirostoma humboldtianum (Valenciennes), en condiciones de cultivo. Se describieron los estadios de desarrollo ovárico y los índices gonadosomático (IG) y hepatosomático (IH). Se realizó una descripción histológica de los ovarios y se midieron los niveles séricos del estradiol (E2) y de la 17α-hidroxi -4-pregnen-3-ona (17-P4) por radioinmunoanálisis. Los resultados mostraron una primera época reproductiva de más de seis meses. Las hembras iniciaron sus desoves a la edad de un año. Se identificaron cuatro estadios de maduración ovárica (estadios I al IV) en la época de desoves y uno más (V) en la época no reproductiva, este último no tuvo un patrón de desarrollo definido. Los valores de los índices IG e IH mostraron una relación lineal positiva con el peso corporal únicamente en la época reproductiva (r² = 0.74 y r² = 0.86, P < 0.05, respectivamente). El análisis histológico de los ovarios indicó que la especie se clasifica como sincrónica por grupos múltiples. Los primeros estadios de maduración gonadal fueron caracterizados por ovarios cuyas poblaciones foliculares estuvieron compuestas predominantemente por folículos previtelinos. Conforme avanzó el proceso de maduración, se observaron todos los estadios de desarrollo folicular, con tendencia al incremento de folículos vitelinos y maduros. Durante el estadio I, las concentraciones de las hormonas esteroides sexuales circulantes de estradiol (E2) y de la 17α-hidroxi-4-pregnen-3-ona (17-P4) fueron altas (2.5 ± 0.7 ng/mL de E2 y 2.4 ± 0.3 ng/mL de 17-P4), se observó un decremento durante el estadio II y los valores más altos se registraron en el estadio IV (7.6± 2.1 ng/mL de E2 y 1.8 ± 0.9 ng/mL de 17-P4). Este mismo patrón fue observado durante la época de no desoves (ANDEVA P < 0.05); estos resultados son los primeros hallazgos en la fisiología reproductiva del pez blanco, los cuales sugieren una temprana actividad esteroidogénica en hembras inmaduras, además de que esta especie conserva su capacidad hormonal en la época posdesove, sustentada en su composición folicular. Lo anterior ayudará para comprender mejor los mecanismos involucrados en los procesos reproductivos y servirá de base para lograr su reproducción controlada y la obtención de huevos y larvas en condiciones de cultivo.
ABSTRACT
The present study describes the external morphology and morphometry of the initial development of Atherinella brasiliensis, and contributes toward broadening knowledge on its biology. A total of 88 larvae and 14 juveniles were used to characterize the morphological development and analyze body proportions. Fish with standard lengths (SL) from 1.4 to 77 mm were used in the study. Larvae hatch at an average of 1.4 mm SL. In the preflexion stage, the larval body is enveloped by a finfold, which begins behind the head. Pectoral fins are the first to be formed and preflexion larvae have four characteristic dendritic chromatophores on the head. The flexion stage begins at an average of 4.4 mm SL; dorsal and anal fins already exhibit pterygiophores and a terminal, somewhat up-turned mouth. At 6.8 mm SL, the flexion stage ends. In the postflexion stage, larvae present greater ossification of the dorsal and anal fin rays, exhibit pelvic fin buds and a darkening of lateral pigmentation. At an average of 8.8 mm SL, head pigmentation intensifies and pelvic fins exhibit conspicuous ossifying rays. Larvae at 11.8 mm SL have all fins formed; the second dorsal fin is the last to be formed at an insertion point posterior to the anal fin. The juvenile period begins at approximately 12 mm SL. At this stage, A. brasiliensis has an anal fin located at the median portion of the body and the posterior end of pectorals surpasses the origin of pelvic fins, which are located at the midpoint between the pectoral and anal fins. Scales are present on the dorsal-lateral region behind the head. The morphological features of A. brasiliensis herein described allow an adequate identification of its larvae and differentiate them from hemiramphid and other atheriniform larvae, thus broadening knowledge on the larval biology of the species
O presente trabalho descreve a morfologia externa e a morfometria do desenvolvimento inicial de Atherinella brasiliensis, contribuindo para a ampliação do conhecimento biológico da espécie. Um total de 88 larvas e 14 juvenis foram empregados para a caracterização do desenvolvimento morfológico e a análise das relações corporais. Peixes com comprimento padrão (CP) de 1,4 a 77 mm foram usados no estudo. As larvas eclodem com CP médio de 1,4 mm. No estágio de pré-flexão, as larvas apresentam o corpo envolvido por uma membrana embrionária, a qual inicia atrás da cabeça. As nadadeiras peitorais são as primeiras a se formarem e larvas em pré-flexão apresentam quatro cromatóforos dendríticos característicos na cabeça. O estágio de flexão inicia com um CP de aproximadamente 4,4 mm, as nadadeiras dorsal e anal já apresentam pterigióforos e uma boca terminal, ligeiramente inclinada para cima. Com um CP de 6,8 mm, o estágio de flexão termina. No estágio de pós-flexão, as larvas apresentam uma maior ossificação dos raios das nadadeiras dorsal e anal, juntamente com o surgimento dos botões das nadadeiras pélvicas e o escurecimento da pigmentação lateral. Com um CP médio de 8,8 mm, a pigmentação da cabeça se intensifica e as nadadeiras pélvicas apresentam raios conspícuos em ossificação. Com 11,8 mm a larva já apresenta todas as nadadeiras formadas, a segunda dorsal sendo a última a ser formada, num ponto de inserção posterior ao da anal. O estágio juvenil inicia-se com aproximadamente 12 mm CP. Neste estágio, A. brasiliensis apresenta a nadadeira anal localizada na porção mediana do corpo, e a extremidade posterior das peitorais ultrapassam a origem das pélvicas, as quais estão localizadas no ponto médio entre as peitorais e a anal. Escamas estão presentes na região dorso-lateral, atrás da cabeça. As características morfológicas das larvas de A. brasiliensis descritas permitem sua adequada identificação, bem como as diferenciam daquelas de hemiramphídeos...