Feeding and reproductive biology of eleotrid fishes in a tropical estuary

Five species of eleotrid fishes ( Gobiomorus dormitor, Dormitator maculatus, Eleotris amblyopsis, Eleotris pisonis and Leptophilypnus fluviatilis ) are known from the Tortuguero estuary of Costa Rica. One, E. amblyopsis , appears tightly linked to the presence of mats of macrophytes and two others, E. pisonis and D. maculatus , are largely limited to this habitat in the lower estuary. All three of these species feed on hyacinth roots. Despite certain food and habitat specializations among the forms, there is evidence of competition and predation among four species. Individuals of breeding size have never been found in the system for D. maculatus and L. fluviatilis . Alternative means of establishing and maintaining eleotrid populations are suggested.     

A preliminary study of two species of flatfish (family: Bothidae) from the south-west Atlantic

Two species of the family Bothidae (lefteye flounders), Mancopsetta maculata metadata and M. milfordi occur in the south-west Atlantic but are caught rarely by commercial bottom trawlers. Little is therefore known about their general biology from this area. A total of 251 M. maculata and 276 M. milfordi were sampled during deep-water exploratory fishing conducted in November 1994 within the Falkland Islands Interim and Outer Conservation Zones, at depths of 400-1000 m, using standard commercial bottom trawling gear. The two species were found to have similar geographical distributions between 48.30'-53.30'S and 55°-62° W and were often obtained at the same stations in depths of 400-900 m on the continental slope. Mancopsetta maculata maculata showed a uni-modal cohort structure with a modal length at the 29-cm total length size-class. Males of M. m. maculata outnumbered females in a ratio of 3.5 : 1. Mancopsetta milfordi showed a tri-modal length distribution, the main mode at the 37-cm total length size-class, with females outnumbering males in a ratio of 1.1 : 1. Length-weight relationships and length-at-age information are presented for the two species. Diet was determined from the analysis of stomach contents and, although the major prey type for both species consisted of crustaceans, the morid fish Austrophycis marginata also formed an important part of the diet of M. milfordi. Key words: Mancopsetta maculata maculata; Mancopsetta milfordi; distribution; south-west Atlantic; size; diet.     

Cladocerans (Branchiopoda) of a tropical estuary in Brazil.

The study was conducted in the Capibaribe river estuary in Recife (Brazil) to assess the role played by cladocerans in a eutrophic environment. Samplings were carried out monthly at 4 fixed stations along the estuary from July 1987 to June 1988. Collections were made with a plankton net of 65 micrometers mesh size. Six cladocerans species were registered: Penilia avirostris, Diaphanosoma spinulosum, Chlydorus barroisi, Ceriodaphnia rigaudi, Ilyocryptus spinifer, and Moina micrura. The most frequent species was Moina micrura with 49%. The only true marine species was Penilia avirostris, which was registered at station 1 (close to the river mouth), during high and low tide and in the dry season. The Cladocera average density decreased from 329 ind.m'3 (August 1987, high tide) to 2 ind.m(-3) (March 1988, high tide) due to the high load of organic and chemical pollution received by the estuary. At all stations, D. spinulosum, M. micrura, and C. barroisi occurred with a wide distribution, mainly during the rainy season. C. rigaudi and I. spinifer were rare, occurring only during the rainy season. Cladocerans played an important role in the food webs of the plankton community of the Capibaribe tropical estuary and the dominance of a few small species indicated a hypereutrophic environment. A high level of disturbance was indicated by the decline in diversity of specialized species and the increase in abundance of opportunistic species like M. micrura.     

Feeding ecology of the waterbirds in a tropical mangrove in the southeast Gulf of Mexico

ABSTRACT

Species that exploit the same type of environmental resources are defined as a guild, which have similar needs in the use of food or habitat. It was analyzed the diet of five waterbirds’ offsprings species (Neotropic Cormorant (Nannopterum brasilianus), Reddish Egret (Egretta rufescens), Boat-billed Heron (Cochlearius cochlearius), Snowy Egret (Egretta thula) and Great Egret (Ardea alba)), by prey identification and calculated the relative importance, overlap and breadth diet. The general diet of the piscivorous guild consisted of 17 fish species from 13 genera and eight families. The highest overlap was between the Reddish Egret and Boat-billed Heron. Fish species dominated the diets of all studied waterbirds, Poecilia velifera was the most abundant prey species in each of the birds, suggesting that they are abundant in the wetlands system of northern Yucatan. Diet overlap in waterbirds species depends on the use of resources and feeding habitat. Since reproductive success largely depends on the availability of food resources, mainly of resident or estuarine fishes. The information about diet is important for the conservation of waterbirds.     

Does the flatfish community of the Mondego estuary (Portugal) reflect environmental changes?

Temporal and spatial patterns of abundance of the flatfish community in the Mondego estuary were investigated from 2003 to 2007, based on monthly beam trawl samples. During the study period there was a severe drought, with consequential reductions in river runoff. A total of eight flatfish species occurred within the estuary, with seasonal specific richness and abundance varying considerably. It was possible to identify three main groups: one composed of species present throughout the study period and in high densities: Platichthys flesus and Solea solea (maximum densities 3.7 and 4.1 Ind 1000 m^?2, respectively); a second group of less abundant but regularly present species: Scophthalmus rhombus and Solea senegalensis (maximum densities 0.2 and 0.3 Ind 1000 m^?2, respectively); and a third group of occasional species that occurred only during the drought period: Arnoglossus laterna, Buglossidium luteum, Dicologlossa hexophthalma and Pegusa lascaris. Flatfish distribution patterns varied according to the estuarine use guild: marine‐estuarine dependent fish occurred mainly in the upper reaches, while marine stragglers and marine‐estuarine opportunists occurred mostly in the downstream areas. Species with more northern latitudinal affinities were the most affected by the drought, related with a lesser extent of river plumes to the coastal area, resulting in a reduction in half of the abundance levels. However, flatfish species with more southern affinities increased in abundance during the drought, benefiting also from an increase in estuarine water temperature. Early summer salinity and precipitation values were good proxies for estimating abundance levels of P. flesus and S. solea, respectively, emphasizing the importance of hydrodynamics for the recruitment and abundance of these commercially important species.     

Distribution and routes of drift migrations in larvae of three species of flatfish Bothus (Bothidae) in open waters of the northern Atlantic

On the basis of large collections, comprehensive data on the distribution of larvae of three species of flatfishes of the genus Bothus (B. ocellatus, B. robinsi, and B. podas) in the northern Atlantic are provided, and the routes of their drift migrations are discussed. Special attention is focused on discussing problems of identification of larvae of the listed species and the specification of evidence on meristic characters of adult flatfishes of these species used for the diagnostics of their larvae. It is shown that larvae of two American species of Bothus carried out from the shelves to the system of western boundary currents are widely distributed in the northern Atlantic drifting in waters of the Northern Subtropical Gyre (NSG). Some of them reach the Azores, and some are drifted along the periphery of the circulation system of the NSG currents towards North America. Unlike larvae of American species, larvae of the eastern Atlantic B. podas perform no transatlantic drift migrations, and the area of their distribution is confined to the waters of the eastern Atlantic. Such differences in the extent of latitudinal passive migrations between B. podas and western Atlantic species are explained according to Torson (1965) by differences in temperature conditions during the drift of larvae of species under comparison that directly affect the decrease (during water temperature increase) or increase (at temperature decrease) of the pelagic phase in their development. The latitudinal drift of larval B. podas from West Africa westwards proceeds due to currents that gradually warm during their motion, which causes a decrease of the dates of their staying in the pelagial. The transatlantic drift of larval American Bothus spp. from North America eastwards is observed in gradually cooling currents, which leads to an increase in the duration and extent of their passive migrations.     

Use of otoliths to determine age and growth of a tropical flatfish Cyclopsetta querna (Paralichthyidae) from the southeast coast of the Gulf of California, Mexico

Age and growth of the tropical flatfish Cyclopsetta querna were determined from the sagittal otoliths. From yearly marginal growth increment trends, it was concluded that the opaque and hyaline zones were formed annually. The oldest individual was a 43.2-cm (5-year-old) female. No significant differences in length-at-age were found between sexes. The von Bertalanffy growth equation for the entire population was L_t = 60.71 (1 − e ^{(−0.245(t−0.408))}). The life span of these species is short, about 5 years. The otoliths proved a reliable structure to determine age of this species.     

A new flounder,monolene helenensis (pleuronectiformes: Bothidae) from the eastern tropical atlantic

Monolene helenensis sp. nov. is described on the basis of seven specimens collected from the eastern tropical Atlantic Ocean. This new bothid flounder differs from all known congeners by the following combination of characters: 108–116 dorsal and 89–92 anal fin rays, 101–111 lateral line scales, 7–10+10–15=18–25 gill rakers, 10–12+37–38=48–50 vertebrae, body depth 2.58–2.77 in standard length, ocular side pectoral fin length 1.34–1.59, in head length and upper half of pectoral fin blackish.     

Feeding strategy,dietary overlap and resource partitioning among four mesopredatory catfishes of a tropical estuary

The feeding strategy, overlap and trophic interactions of four demersal catfishes inhabiting Cochin Estuary, Arius maculatus (n = 67), A. subrostratus (n = 63), A. arius (n = 21) and Mystus gulio (n = 69) were investigated through gut-content analyses. The indices of relative importance revealed that the prey items in their stomachs were dominated by crustaceans except in A. arius where molluscs constituted the major prey item. The highest diet and niche breadth values (3.93, 0.36 respectively) were recorded in A. subrostratus, while the lowest was recorded in A. arius (2.64, 0.23 respectively). Pianka's overlap, calculated through null models constructed by Ecosim 7.0, revealed significant niche overlap between A. maculatus and A. subrostratus (O–0.91, P < 0.001), between A. maculatus and M. gulio (O–0.72, P < 0.05) and between A. subrostratus and M.gulio (O–0.64 P < 0.05). However, no overlap was recorded between A. arius and other species. The trophic niche breadth along with prey specific abundance confirmed that these fishes are highly specific feeders. The present results on trophic level status indicate that these catfishes are mid-level carnivores that can be considered as moderate benthic mesopredators and are specialist feeders unlike most catfishes.     

Movement patterns of catfishes (Ariidae) in a tropical semi‐arid estuary

From December 2005 to November 2006, 216 samples were taken from the main channel of the Goiana Estuary, representing a total sampled area of 23 ha. Ariidae species were the most abundant in density (1600 individuals ha^?1, 53%) and biomass (18 813 g ha^?1, 63%). Cathorops spixii was the most abundant in density (1340 individuals ha^?1) and biomass (14 203 g ha^?1). The variables: number of species, total density and biomass, showed significant interactions between the factors of areas and seasons (P < 0·01). The highest total density (7394 individuals ha^?1) and biomass (70 292 g ha^?1) occurred in the middle and upper estuaries, respectively, during the early‐rainy season. The density of C. spixii differed significantly between areas and seasons (P < 0·01), while Cathorops agassizii differed significantly only between seasons (P < 0·01). The biomass differed significantly for the species C. spixii, C. agassizii and Sciades herzbergii between seasons, and C. spixii and C. agassizii between areas. Also, the density and biomass of C. spixii and C. agassizii showed interaction between areas and seasons. Only the biomass of S. herzbergii showed interaction between areas and seasons (P < 0·01). This indicates that seasonal variations influenced the distribution of Ariidae species in the different areas of the Goiana Estuary. Moreover, canonical correspondence analysis highlighted a strongly significant correlation (P < 0·01) between the seasonal variations of the environmental gradients (salinity and water temperature) and distribution of catfishes. The management and conservation of estuaries should take into account the life cycle of these species in different estuarine areas and hydrological seasons.     

Flower biology of the cactus Coryphantha elephantidens in the tropical dry forest of Central Mexico

Floral traits and sexual systems in angiosperms are strategies that enhance outcrossing within hermaphrodite flowers and among individuals in a population. Sexual systems with unisexual flowers have also evolved among angiosperms, resulting in sex specialization. Furthermore, the interaction of floral traits and floral visitors determines successful plant reproduction. Globose cacti are bee pollinated, and variation in the diversity of their pollinator assemblages is strongly associated with floral phenotype. Our objective was to describe the floral biology of the cactus Coryphantha elephantidens and to determine its relationship with pollinators. Floral traits were studied by direct observations in live and fixed flowers. The breeding system was determined using two estimators based on floral morphology: pollen grains to ovules per flower (P/O) ratio and outcrossing index. Pollination treatments were conducted to determine the mating system. Floral visitors were recorded using direct observation. Flowers of C. elephantidens are variable in color, protandric, herkogamous and nectarless. Estimators of the breeding system indicated xenogamy, which is consistent with the obligate outcrossing revealed by the pollination experiment. Thirty-seven percent of the plants have female flowers that do not produce pollen, making this population functionally gynodioecious. Both fruit and seed set were high compared to other globose cacti. Pollinators included eight species of native bees, a more diverse pollinator assemblage than other globose cacti. Given the high pressure on pollen due to functional gynodioecy, nectarless flowers, an outcrossing mating system, and the necessity of pollinators to set seeds, we concluded that native bees are highly efficient pollinators that play a crucial role in the sexual reproduction of C. elephantidens.     

Trophic resource partitioning among five flatfish species (Actinopterygii, Pleuronectiformes) in a tropical bay in south-eastern Brazil

Five species of flatfishes in a tropical bay in south-eastern Brazil were studied to test the hypothesis that resource partitioning along the spatial and size dimensions has been used as a mechanism to enable coexistence. Three zones in the study area were defined according to environmental characteristics (inner, middle and outer). Sampling was conducted by otter trawl tows during daylight hours, between October 1998 and September 1999. Achiridae species ( Achirus lineatus and Trinectes paulistanus ) showed narrow niche width, indicating a specialized feeding strategy, preying on Polychaeta, and occurring mainly in the inner bay zone. Paralichthyidae ( Citharichthys spilopterus and Etropus crossotus ) and the Cynoglossidae ( Symphurus tessellatus ) showed broad niche width and a generalized feeding strategy preying on a large number of Crustacea. Symphurus tessellatus did not change diet with size-dimension feeding on Amphipoda and Polychaeta, whereas C. spilopterus and E. crossotus shifted diet with growth. Citharichthys spilopterus fed mainly on Mysida and secondarily on shrimps, with juvenile preying on large amounts of Calanoida, whereas adults consumed large amounts of fishes. Isaeidae amphipods were a significant prey for both small and large E. crossotus , whereas Polychaeta Errantia were used mainly by large fishes. Etropus crossotus and S. tessellatus share similar feeding resources in outer bay zone preying on Isaeidae and Polychaeta Errantia. Differences in the Pleuronectiformes diet composition along with spatial and size changes in the use of the available resources contributed to allow the organisms' coexistence in Sepetiba Bay. The high item diversity used by flatfishes indicates that the system plays an important role as a feeding ground, and that interspecific competition for food was unlikely.     

Reproductive biology of the tropical fish Trichogaster pectoralis (Regan)

The breeding cycle of an air-breathing Anabantid, Trichogaster pectoralis was studied in Malaysia. The species was found to breed all the year but with pronounced peaks of activity associated with the two wetter periods in the year. The advantages of this timing and the cues which stimulate gonadal activity are discussed. From the study of oocyte distribution in selected ovaries it was concluded that T. pectoralis is a total spawner although a batch of ripe oocytes may be released over an extended period of time. Fecundity was found to be related to length of fish by the formula (log₁₀ Egg no.)=–4.6854+4.3080 log₁₀ standard length (S.L.) (mm).     

Steady state of phytoplankton assemblage in the tropical Lake Catemaco (Mexico)

Phytoplankton of the tropical lake Catemaco (Veracruz, Mexico) showed similar species composition during samplings from 1993 to 1995. There were two small dominant cyanobacterial species Cylindrospermopsis catemaco Kom.-Legn. et Tavera and Cylindrospermopsis philippinensis (Taylor) Kom., and a group of larger algae and cyanobacteria that were always present, however in smaller numbers: Aulacoseira granulata (Ehr.) Simons morphotype curvata, A. cf. italica (Ehr.) Simons mf. curvata, Fragilaria construens (Her.) Grun., Achnanthes minutissima Kütz., Planktolyngbya circumcreta (G.S.West) Anagn. et Kom., Chroococcus microscopicus Kom.-Legn. et Cronberg. Moreover we found several other scarcely present species. The percentage of total biomass of the two dominant species of Cylindrospermopsis varied between 34 and 81%, but they accounted for 80 to 95% of abundance. Apart from geomorphological features and climate conditions, biological variables played an important role. Fish-stock was formed by filter-feeding native herbivorous species of fish Dorosoma petenense (Günther), Bramocharax caballeroi (Contreras et Rivera), Astyanax mexicanus (Filippi), and an introduced, also herbivore Oreochromis niloticus (L.). Feeding activity of fish removed large species of algae and cyanobacteria as well as detrital remnants and zooplankton from the water. Smaller, inedible cyanobacteria remained in the water and formed the stable portion of the phytoplankton, dominant both in biomass and abundance. CANOCO analysis of samples and species variability demonstrated results of competition between two species of Cylindrospermopsis: steady state during the dominance of C. catemaco lasting probably for the whole year 1993 (one dry and one wet season) and steady state during the dominance of C. philippinensis in 1994 and 1995. According to the functional classification of phytoplankton suggested by Reynolds et al. (2002), Catemaco dominant assemblage would belong to the functional group S _N.     

Feeding ecology of the American freshwater goby Ctenogobius shufeldti (Gobiidae, Perciformes) in a sub-tropical estuary

The feeding ecology of the American freshwater goby Ctenogobius shufeldti in a low salinity salt-marsh habitat in the Paranaguá Bay estuarine complex (Brazil) was assessed through the gut analysis of 632 individuals. The effects of a set of abiotic factors (type of sediment, salinity, temperature and estuarine reach), season and body size on dietary composition were analysed. Seasonal and size-related changes in feeding strategy, feeding intensity and trophic level were assessed. The effects of gape and body size on prey size use were also analysed. The results showed that C. shufeldti is a typical omnivorous, generalized benthic predator of low trophic levels throughout the seasons and size classes, feeding on 56 dietary items; tanaids, chlorophyte algae, ostracods, gastropods, detritus and benthic diatoms made up the bulk of its diet. The tanaid Kalliapseudes schubarti was the main prey item in both numerical and volumetric terms. The gut fullness was persistently high across the seasons. As expected for a typical generalized, opportunistic omnivorous feeder: (1) seasonal and spatial-temporal variability of abiotic factors had a significant effect on diet structure, (2) season accounted for most of the dietary variation and (3) diet composition and the size of prey consumed did not vary across the size classes.     

Early life history stages of peacock flounder Bothus lunatus (Bothidae) from the western and central tropical Atlantic

Previously unknown larvae and poorly studied metamorphic and postmetamorphic stages of development of peacock flounder Bothus lunatus (Bothidae) with a length of 5.4 to 39.5 mm from the western and central tropical waters of the Atlantic Ocean are described, and their identification is substantiated. Small-and medium-sized larvae of this species (with a length of nearly 10 mm) at stages of pre-and postflexion, like all larvae of the genus Bothus at the corresponding stages of development, have a strongly flattened from the sides, moderately deep, and almost pigment-free transparent body; bear a long anterior ray in the dorsal fin; and have single melanophores in the end part of the body. They differ from larvae of other Atlantic species of the genus known at early stages of development in the shape of the anterior head profile, namely in the presence of a deep notch in front of the eyes. With growth, their body assumes a rounded shape. During metamorphosis of larval B. lunatus, the right eye shifts to the left side of the head through a slit formed during the separation of the origin of dorsal fin base from the cranium. This specific feature distinguishes them from larvae of the remaining species of the genus in which, during metamorphosis, the right eye passes to the left side through the hole in the head.     

Adaptation in the jaws of flatfish (Pleuronectiformes)

The structure and mechanisms of the jaws of 18 species of flatfish have been investigated. Clear adaptations to different modes of feeding were found. The mechanisms of the jaws of Soleidae, Cynoglossidae, and Rhombosoleinae are highly specialized and the representatives of the two latter groups have some interesting jaw muscles of doubtful homology.     

Feeding ecology and growth of O-group flatfish (sole, dab and plaice) on a nursery ground (Southern Bight of the North Sea)

The food composition of O-group sole Solea solea , dab Limanda limanda and plaice Pleuronectes platessa on a nursery ground at Gravelines, France, included 17–25 taxa. Sole (new settlers) fed mainly on harpacticoid copepods and when 50 mm in size, on polychaetes (Terebellidae). Dab (<40 mm) consumed mainly polychaetes (Magelonidae and Spionidae), and later amphipods, polychaetes (Spionidae) and Hydrozoa. O-group plaice diet was dominated by polychaetes (Terebellidae), crustaceans and molluscs at all sizes. O-group sole, dab and plaice did not compete for food resources, each species being specialized in different prey items. Growth rates during May-July 1998 varied between 0·5 and 0·67 mm day⁻¹ for sole, 0·12 and 0·24 mm day⁻¹ for dab and 0·55 and 0·81 mm day⁻¹ for plaice. For sole and plaice, these estimates were similar to those recorded in other nurseries and also close to the maximal growth predicted by experimental models. This suggests that their growth was not limited by food during the first summer of life.