Age structure and growth of peacock cichlids from rivers and reservoirs of Venezuela

Cichla temensis collected in Venezuela attained a mean standard length of 440 mm, and C. orinocensis and C. intermedia mean lengths of 309 and 321 mm, respectively. There was little evidence of size differences between sexes. Opaque zones on otoliths corresponded to the period of peak of reproductive activity and low fish body condition ( K ). When aggregated across sites, linear estimates for growth of fish >age I were 57·5, 27·6, and 19·6 mm year¹ for C. temensis , C. orinocensis , and C. intermedia , respectively. Fish from the Cinaruco River appeared to spawn at age I, and prior to first maturation had grown 25, 21, and 23 mm month¹, respectively, for C. temensis , C. orinocensis , and C. intermedia . There was little intersite variation in growth rates, and differences in sizes of conspecifics from different sizes were due to age differences. Cichla in captivity spawn several times per year. The present results indicate that the annual cycle or tropical wet/dry seasonality promotes reproductive seasonality in Cichla . The energetic cost of reproduction and brood defence probably constrains most individuals to one spawn per year. Conversely, populations living in relatively aseasonal reservoir environments may have several spawns per year, in which case growth zones on hard structures are difficult to interpret.     

Systematics, biogeography, and evolution of the Neotropical peacock basses Cichla (Perciformes: Cichlidae)

To investigate forces influencing diversification in Neotropical fishes, the phylogenetic relationships among species and populations of the cichlid genus Cichla were examined. Mitochondrial DNA was sequenced for 454 individuals of the 5 nominal Cichla species and several putative undescribed species. Phylogenetic analyses support the distinction of two major clades of Cichla. Clade A includes C. temensis and two undescribed species from the lower Amazonas and Xingu Rivers. Clade B includes C. orinocensis, C. monoculus, C. ocellaris. C, intermedia, and an undescribed species from the upper Madeira River. Species boundaries were relatively well-circumscribed for clade B, while incomplete lineage sorting was inferred for clade A. Three probable instances of introgression were observed, including a regional population of C. orinocensis from the Negro River that shows a history of introgression. Biogeographic patterns from Cichla are partially congruent with those seen in several other Neotropical fish clades, and the diversification of Cichla species is inferred to result from both vicariance and sympatric divergence.     

Influence of life history and seasonal hydrology on lipid storage in three neotropical fish species

The seasonal dynamics of energy (lipid) storage in three neotropical fish species with differing life histories were evaluated. Lipid content was substantially greater in the liver than in dorsal musculature of all three species. Two piscivores ( Cichla temensis and Serrasalmus manueli ) showed large, statistically significant seasonal fluctuations in liver lipid content. Liver lipid content increased during high water, through the falling water, and into the early dry season for both piscivores. Seasonal variation in dorsal muscle lipid content was large and statistically significant for C. temensis , but was small and non‐significant for S. manueli . Cichla temensis appeared to 'finance' costs associated with reproduction by accumulating lipids during the falling‐water period when migratory prey allowed the species to subsidize their energetic dynamics. Semaprochilodus kneri , a migratory algivore and detritivore, showed no significant seasonal variation in dorsal muscle lipid content and minimally significant seasonal variation in liver lipid content. Statistically significant effects of lipid content on δ¹³C was observed when tissue lipid content varied by >12%, while biological interpretation of food web statistics based on δ¹³C values appears robust to minor variations in lipid content. Nonetheless, when lipid content varied by larger amounts ( e.g . >35% for C. temensis and S. manueli liver tissue) lipids appeared to have a large potential effect on δ¹³C and food web statistics calculated from such measurements may have been biased. Surprisingly, even large variation in tissue lipid content did not affect δ¹⁵N.     

Karyological evidence for interspecific hybridization between Cichla monoculus and C. temensis (Perciformes, Cichlidae) in the Amazon

Cichla monoculus, Cichla temensis (peacock bass or tucunare), and its presumed hybrids, were cytogenetically analyzed. The fish were collected at three distinct sites in the central Amazon basin, namely in the Uatuma (C. monoculus, C. temensis and their natural hybrid), Jau (C. temensis), and Solimoes rivers (C. monoculus). The two species and the natural hybrid showed the same diploid number, 2n=48 acrocentric chromosomes. Single NORs were detected in the distal region of the long arm in all three species. However, in C. monoculus, the NOR was found on the second pair of the complement, in C. temensis, on the third pair and in the hybrid two NOR patterns were found, one on the second pair and the other on the third pair of chromosomes. The two species and the hybrid have their constitutive heterochromatin located in the pericentromeric region of all chromosomes and an interstitial C-band located on the largest chromosome pair. The great similarity in the chromosome number and morphology, chromosome size class differences, the NOR patterns and C-banding suggested chromosomal stasis during speciation and hybridization of Cichla.     

Permanent Genetic Resources added to Molecular Ecology Resources Database 1 April 2012 - 31 May 2012

This article documents the addition of 123 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Brenthis ino, Cichla orinocensis, Cichla temensis, Epinephelus striatus, Gobio gobio, Liocarcinus depurator, Macrolophus pygmaeus, Monilinia vaccinii-corymbosi, Pelochelys cantorii, Philotrypesis josephi, Romanogobio vladykovi, Takydromus luyeanus and Takydromus viridipunctatus. These loci were cross-tested on the following species: Cichla intermedia, Cichla ocellaris, Cichla pinima, Epinephelus acanthistius, Gobio carpathicus, Gobio obtusirostris, Gobio sp. 1, Gobio volgensis, Macrolophus costalis, Macrolophus melanotoma, Macrolophus pygmaeus, Romanogobio albipinnatus, Romanogobio banaticus, Romanogobio belingi, Romanogobio kesslerii, Romanogobio parvus, Romanogobio pentatrichus, Romanogobio uranoscopus, Takydromus formosanus, Takydromus hsuehshanesis and Takydromus stejnegeri.     

Refugees or ravenous predators: detecting predation on new recruits to tropical estuarine nurseries

Many of the most abundant small and juvenile fishes within shallow water estuarine nursery habitats consume other fish to some degree but have rarely been considered as potentially important predators in the functioning of these systems because of the low (<50%) average occurrence of fish in their diets. Predation by abundant minor piscivores on new recruits when they first enter the nursery may make a significant contribution to the predation mortality of this critical life-history stage. To determine the potential importance of minor piscivores as predators on new recruits, temporal patterns in the diets of 15 common species of minor piscivores were examined and related to the abundance of new recruits (≤20 mm FL) in biweekly seine samples over 13 months in shallow (<1.5 m) sandy habitats in the Ross River estuary in north-eastern Queensland, Australia. The high spatial patchiness of new recruits made it difficult to correlate their abundance with their consumption by minor piscivores, and there was no relationship detected between the abundance of new recruits and the occurrence of fish in the diets of minor piscivores. To gain broader insight into spatio-temporal patterns in the consumption of fish prey by minor piscivores, we utilised a collection of fishes sampled during various studies over 6 years from 17 estuaries in the region to examine the diets of >3500 individuals from 20 spp. of minor piscivores. Patterns in the consumption of fish prey by these minor piscivores, especially the highly abundant sparids, sillaginids and ambassids, revealed that the low average occurrence of fish in their diet greatly underestimated the predation pressure imposed by these on fish prey at particular locations and times. For most sampling occasions and locations few minor piscivores consumed fish prey (consumed by 0% of individuals examined), while occasionally a large proportion of individuals within a taxon did so (50–100% of individuals consumed fish prey). Often at such times/locations multiple species of minor piscivores simultaneously preyed heavily on fish. When minor piscivores consumed fish, they preyed mainly on small new recruits. Because many of these minor piscivores are relatively recent recruits, many of the small and juvenile fishes believed to gain refuge in shallow estuarine nurseries may themselves be important predators on fish subsequently recruiting to these habitats, and so potentially play a significant role in structuring estuarine fish faunas and the functioning of shallow water nurseries.     

Consistent trophic patterns among fishes in lagoon and channel habitats of a tropical floodplain river: Evidence from stable isotopes

The relationship between food web dynamics and hydrological connectivity in rivers should be strongly influenced by annual flood pulses that affect primary production dynamics and movement of organic matter and consumer taxa. We sampled basal production sources and fishes from connected lagoons and the main channel of a low-gradient, floodplain river within the Orinoco River Basin in Venezuela. Stable isotope analysis was used to model the contribution of four basal production sources to fishes, and to examine patterns of mean trophic position during the falling-water period of the annual flood cycle. IsoSource, a multi-source mixing model, indicated that proportional contributions from production sources to fish assemblages were similar in lagoons and the main channel. Although distributions differed, the means for trophic positions of fish assemblages as well as individual species were similar between the two habitats. These findings contradict recent food web studies conducted in temperate floodplain rivers that described significant differences in trophic positions of fishes from slackwater and floodplain versus main channel habitats. Low between-habitat trophic variation in this tropical river probably results from an extended annual flood pulse (ca. 5 mo.) that allows mixing of sestonic and allochthonous basal production sources and extensive lateral movements of fishes throughout the riverscape.     

Fish feeding guilds in shallow rocky and soft bottom areas on the Swedish west coast

Multivariate analyses of the diet relationships within fish assemblages resulted in the recognition of five major feeding guilds in shallow (0-9 m) rocky- and soft-bottom habitats on the Swedish west coast. The two habitats had similar guilds that could be broadly described as piscivores, decapod feeders, copepod feeders and amphipod and mollusc feeders. The last guild on the rocky bottom was more strictly one of amphipod feeders, whereas the last guild on soft bottoms consisted of infauna feeders (mainly polychaetes and bivalves). A comparison of the diet of the entire fish assemblages showed that amphipods and gastropods were more prevalent as prey taxa on rocky bottoms, whereas bivalves and teleosts were more common on soft bottoms. A large proportion (12 out of 27 species) of the fish species investigated was found in both habitats. These fish species generally seemed to rely on the same major prey groups in the two habitats, but also included prey taxa characteristic for the habitat in which they resided. Sea trout Salmo trutta , mackerel Scombrus scombrus , saithe Pollachius virens , whiting Merlangius merlangus and cod Gadus morhua were found to be the major piscivores in both the investigated habitats. Herring Clupea harengus and members of the family gobiidae were the most prevalent prey species for piscivores within the rocky- as well as the soft-bottom fish assemblage. A comparison of feeding modes suggested that the fish assemblage on rocky bottoms predominantly (60% of the food items) relied on food found in vegetation. On soft bottoms, the average distribution of food categories among fish species was 44% benthic, 35% pelagic and 21% vegetation-associated food items.     

Evidence for a natural hybrid of peacock bass (Cichla monoculus vs Cichla temensis) based on esterase electrophoretic patterns

Esterase (Est) and esterase-D (Est-D) electrophoretic patterns identified by starch gel electrophoresis of skeletal muscle protein extracts of 184 specimens of three species of peacock bass, locally known as tucunares (Cichla monoculus, C. temensis and Cichla sp), plus four specimens of a supposed hybrid (C. monoculus vs C. temensis), collected from the Central Amazon, were examined to determine if they could aid in identifying a supposed hybrid between C. monoculus and C. temensis. Six zones of electrophoretic activity were found with these enzyme systems. The Est enzyme showed one zone of activity, formed by bands 1, 2 and 3, plus three zones of activity, presumably controlled by Est-1, 2 and 3 loci. The Est-D enzyme had two zones of activity, presumably controlled by Est-D1 and Est-D2 loci. Cichla monoculus and C. temensis shared band 2 and alleles Est-1(1), Est-2(1), Est-3(2), and Est-D1(1), and therefore these were useless for identifying hybrids between the two species. However, a probable hybrid pattern of bands 1, 2, and 3, presumably generated by a combination of pattern 12 from C. monoculus with pattern 23 from C. temensis, resulting from a possible cross between these two species, was detected. Although the Est-D2 locus cannot be considered an ideal diagnostic marker for identifying the supposed hybrid (C. monoculus vs C. temensis), as it is polymorphic, it proved to be useful for determining the origin of the hybrid, i.e., which parental species were involved in the hybridization process.     

模糊数学方法模拟水库运行影响下鱼类栖息地的变化

水库调度改变了河流水文情势,从而使得水生动植物栖息地的空间分布发生明显的变化。针对水库运行对鱼类栖息地的影响,利用模糊数学方法建立栖息地模型,并与水环境模型耦合,分析不同水文情势下鱼类在不同生长期的栖息地变化情况。基于专家分析法建立模糊函数隶属度及规则集,计算栖息地适宜性指数(HSI),提出适宜栖息地宽度指数(HSWI)表征河道内栖息地连通性,并对栖息地变化的有效性进行分析。选取漓江下游的某个复式河道为对象,模拟特征鱼种光倒刺鲃(Spinibarbus hollandi)在典型水文年份中水库不同调节模式下的栖息地变化情况。结果表明,在丰水年及枯水年的产卵期,水库补水明显增加了鱼类适宜栖息地面积,其中高适应性区域面积增幅近50%,而平水年影响较小;水库补水对越冬场的影响则相对微弱,仅增加5%左右。     

Ontogenetic diet shifts and resource partitioning among piscivorous fishes in the Venezuelan ilanos

Synopsis Resource utilization by nine abundant piscivores from a diverse tropical fish assemblage was examined over the course of a year. All nine species exhibited peak reproduction during the early wet season and a similar sequence of size-dependent shifts from a diet composed primarily of microcrustacea, to aquatic insects, and finally fishes. Three piranha species specialized on fish fins, particularly at subadult size classes (SL 30–80 mm). Gradual dessication of the floodplain during the transition season was associated with fish growth, increased fish density, and decreased aquatic primary productivity and availability of invertebrate prey. Based on 118 resource categories, average pairwise diet overlap was low during all three seasons: wet, transition, and dry. Of 72 species pairings, only one pair of fin-nipping piranhas exhibited high overlap simultaneously on three niche dimensions: food type, food size, and habitat. Adults of two species, a gymnotid knifefish and pimelodid catfish, were largely nocturnal. Patterns of habitat utilization indicate that piranhas may restrict diurnal use of the open-water region by other piscivores. Collective diet overlap of individual piscivore species with the other eight feeding guild members and collective overlaps with the entire fish community each revealed two basic seasonal trends. Four species that showed an early switch to piscivory also showed a high degree of diet separation with both the guild and community at large on a year-round basis. The five remaining species showed lowest collective diet overlaps during the transition season when availability of invertebrates was reduced and fish densities were maximal. Whereas predation may play a role in habitat separation, diffuse competition for food resources during the approximately four-month transition season probably is the principal factor yielding patterns of diet specialization.     

Profile of micronucleus frequencies and DNA damage in different species of fish in a eutrophic tropical lake

Lake Paranoá is a tropical reservoir for the City of Brasilia, which became eutrophic due to inadequate sewage treatment associated with intensive population growth. At present, two wastewater treatment plants are capable of processing up to 95% of the domestic sewage, thereby successfully reducing eutrophization. We evaluated both genotoxic and cytotoxic parameters in several fish species (Geophagus brasiliensis, Cichla temensis, Hoplias malabaricus, Astyanax bimaculatus lacustres, Oreochromis niloticus, Cyprinus carpio and Steindachnerina insculpita) by using the micronucleus (MN) test, the comet assay and nuclear abnormality assessment in peripheral erythrocytes. The highest frequencies of MN were found in Cichla temensis and Hoplias malabaricus, which were statistically significant when compared to the other species. However, Steindachnerina insculpita (a detritivorous and lake-floor feeder species) showed the highest index of DNA damage in the comet assay, followed by C. temensis (piscivorous). Nuclear abnormalities, such as binucleated, blebbed, lobed and notched cells, were used as evidence of cytotoxicity. Oreochromis niloticus followed by Hoplias malaricus, ominivorous/detritivotous and piscivorous species, respectively, presented the highest frequency of nuclear abnormalities, especially notched cells, while the herbivorous Astyanax bimaculatus lacustres showed the lowest frequency compared to the other species studied. Thus, for biomonitoring aquatic genotoxins under field conditions, the food web should also be considered.     

Timing of the diet shift from zooplankton to macroinvertebrates and size at maturity determine whether normally piscivorous fish can persist in otherwise fishless lakes

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Food and feeding ecology of piscivorous fishes at Lake St Lucia, Zululand

The food and feeding ecology of piscivorous fish in Lake St Lucia was monitored for two years. Piscivorous fishes feed predominantly on the planktivorous Gilchristella aestuarius and Thryssa vitrirostris but a wide range of prey species was recorded. Numbers of the predominant piscivores, Argyrosomus hololepidotus and Elops machnata , in an area appear to be related to the densities of their major prey, T. vitrirostris and G. aestuarius . Large piscivorous fishes are restricted to the deeper portions of the lake, whereas small piscivores such as Johnius belengerii and Terapon jarbua feed predominantly on small fishes in the littoral zone. The highly significant correlation between the composition of prey fish species in the lake and prey fish species in the diet of piscivorous fishes, indicates that piscivores are feeding in a density dependent manner. However, factors such as habitat, fish size and swimming speed of prey species are shown to be important in prey selection. Juvenile fish of species such as Sarotherodon mossambicus, Liza macrolepis and Acanthopagrus berda remain in shallow marginal areas, thus avoiding large piscivorous fishes. However by frequenting shallow areas these species become vulnerable to bird predators, especially egrets and herons.     

Seasonal biomass and diversity of estuarine fishes coupled with tropical habitat heterogeneity (southern Gulf of Mexico)

Nekton dynamics were studied in two contrasting habitats in Terminos Lagoon, Mexico. Over an annual cycle, a total of 83 fish species used the high-salinity fringing mangrove/ Thalassia testudinum habitat and biomass ranged from 0.43 to 3.43 g m⁻². The highest biomass occurred during the dry season when aquatic primary production was highest (i.e. 333 g C m⁻² year⁻¹). By contrast, 65 species used the freshwater and low-salinity riverine mangrove/Crassostrea virginica/Vallisneria habitat and biomass ranged from 0.57 to 1.48 g m⁻² with the highest biomass occurring during the wet season, the time of highest primary production in this habitat (i.e. 219 g C m⁻² year⁻¹). The high- and low-salinity habitats serve as ecological bridges between freshwater areas and the sea. Fish life histories have evolved to utilize these habitats for spawning, feeding and nursery grounds in a manner which generally leads to the use of different habitats during the periods of highest primary productivity.     

Piscivorous fishes diet dominated by the Asian cyprinid invader,topmouth gudgeon (<Emphasis Type="Italic">Pseudorasbora parva</Emphasis>)

Predation on the non-native cyprinid, Pseudorasbora parva, was reported during an annual study in a small connecting canal about 40 km south of Brno, Czech Republic. Two cyprinid fish species (Pseudorasbora parva, Rutilus rutilus) were identified in the diet of 23 piscivores belonging to three native fishes (Perca fluviatilis, Sander lucioperca, Esox lucius). The relative abundance of prey fishes changed seasonally and was dominated by the topmouth gudgeon in spring. Thereafter roach incidence continuously increased. In contrast, topmouth gudgeon was found to be a more sized-available prey and was the most dominant prey species in the diet of all piscivorous fishes during the whole season. Strong piscivory towards this alien might be beneficial for its eradication or control to support ecological integrity in natural and modified seminatural habitats.     

The ecology, behavior, and conservation of the tidewater goby, Eucyclogobius newberryi

Understanding the ecology and behavior of endangered species, such as the tidewater goby, Eucyclogobius newberryi, is important for identifying problems and formulating solutions for species recovery. The tidewater goby forms isolated populations in California's coastal lagoons, creeks, and marshes. Rapid declines in the number of populations led to its listing as an endangered species in 1994. This benthic fish prefers stillwater habitats and feeds on small invertebrates. It is an annual species with an extended breeding season. Fish are larger in marsh habitats than in lagoon or creek habitats. The male digs a spawning burrow, preferably in sand, where he provides care for a single clutch. The tidewater goby is sex-role reversed: females compete more intensely than males for access to mates. The tidewater goby is a species at risk, in part due to narrow habitat preferences, isolation of populations, short lifespan, lack of marine dispersal, and vulnerability to introduced predatory fishes. Attributes that favor its recovery include euryhaline tolerances, rapid reproductive rate, its potential for opportunistic feeding, and the possibility of natural recolonization under certain circumstances. Potential conservation measures include protecting coastal marshes that adjoin creeks and lagoons, maintaining natural hydrologic regimes, preventing artificial breaching of the sandbar at the estuary's mouth, and preventing introductions of predatory fishes. Captive breeding and reintroduction of tidewater gobies are potential tools for recovery, provided that underlying problems of habitat availability and suitability and issues of genetic integrity and disease transmission are addressed. Further research into the tidewater goby's utilization of marsh habitats, dispersal mechanisms, response to artificial breaching events, and metapopulation genetics would provide additional information for management.     

Seasonal resource selection by blue suckers Cycleptus elongatus

Telemetry data were used to quantify seasonal resource selection and rank‐preferred habitat types for blue suckers Cycleptus elongatus in the middle Missouri River and its tributaries, Iowa, Nebraska, South Dakota, U.S.A. Habitat diversity required by C. elongatus to complete its annual life‐history cycle was evident by interseasonal variation in habitat selection. Tributaries and unchannelized portions of the middle Missouri River system were selected during the inferred spawning season (spring), habitats along shorelines in the channelized middle Missouri River were selected for postspawning (summer) and areas of reduced current were generally selected for the period preceding spawning (autumn). This study provides insight into mature C. elongatus behaviour throughout its annual life cycle. Furthermore, these results document the interseasonal variability in habitat selection of C. elongatus and highlight the need for development of habitat selection models for other imperilled fish species in aquatic systems affected by anthropogenic developments.     

Long-term investigations of migratory behaviour of asp (Aspius aspius L.) in the middle part of the Elbe River, Germany

The migratory behaviour, habitat use, home range and temporal and spatial variability of migrations of the potamodromous asp (Aspius aspius L.) in the large Elbe River, Germany, were studied in the years 1997–2000. Fifty‐three asp were tagged with surgically implanted radio transmitters and individually hand‐tracked usually once per week for about 1 year; 50% of the asp exclusively inhabited the main channel, 22% moved for short visits into other habitats and 24% changed between winter habitats in a harbour or oxbow and summer habitats in the main channel where they spawned in late March/April. The migratory behaviour of asp was highly variable; 34 asp observed for more than 1 year lived in home ranges of 1 to >100 stream kilometres (skm) mostly near their capture site. Longest observed migration from summer habitat in the Tidal Elbe back to the spawning ground in the Middle Elbe was 166 skm. After the spawning period or the spawning period thereafter, nine of these 34 fish left their home ranges for a long downstream migration without returning during the observation period. From these results we conclude that populations of rheophilic, potamodromous fish use a surprisingly long river section and that weirs have a strong impact on migration patterns and, ultimately, on population dynamics of these species.     

Diet composition of bluefin tuna (Thunnus thynnus L. 1758) in the Eastern Mediterranean Sea,Turkey

This study gives relevant information on the diet composition of the bluefin tuna (Thunnus thynnus) during the spawning period in the eastern Mediterranean Sea. The stomach contents of 218 bluefin tuna were sampled from 2003 to 2006 during the fishing season (May–June) aboard purse seiners operating in the northern Levantine Sea off the coast of Turkey. Stomachs were removed from the fish soon after landing and kept frozen at ?18°C until analysis. Prey items were classified into large taxonomic categories and preserved in 70% ethanol. A total of 745 different prey specimens belonging to 47 taxa were identified, including 34 species of fish, 11 of squid, and two of crustaceans. The most important fish and cephalopod prey belonged to the families Myctophidae, Carangidae, Chauliodontidae, Paralepididae, and Octopoda. This study marks the observation of myctophid fish in the stomach contents of bluefin tuna from the Mediterranean Sea. The paper offers some new information of regional importance and compares the feeding habits of the species to other regions, bringing confirmation on the opportunistic feeding ecology of the species in the enclosed Mediterranean Sea, where bluefin tuna seasonally occur as a strong cohort. New information on the diet composition of T. thynnus in the eastern Mediterranean Sea is revealed; the findings indicate that, depending on the abundance of the different prey species in the habitat, the dominant prey species can be distinctive.