Interaction between the introduced eastern mosquitofish and two autochthonous Spanish toothcarps

In aquaria, adults and young-of-the-year (YOY) of both Spanish toothcarp Aphanius iberus and Valencia toothcarp Valencia hispanica received more aggression in the presence of eastern mosquitofish Gambusia holbrooki . YOY of both species also showed decreased feeding rates, as did V. hispanica adults. Adult V. hispanica also were more aggressive themselves and had their reproductive behaviour disrupted. Cases of eastern mosquitofish predation on small A. iberus were also observed. The occurrence and intensity of these potentially harmful effects, however, seemed to be modulated by water temperature, reproductive condition, relative size of the interacting fishes and species-specific habitat preferences. Thus, aggression almost disappeared at low water temperatures. Valencia hispanica and eastern mosquitofish used similar vertical positions in the water column and this apparently increased the frequency of their interactions. In contrast, A. iberus preferred positions closer to the bottom than the other two species and this vertical segregation appeared to lead to less direct interaction with eastern mosquitofish. In an outdoor mesocosm experiment, under semi-natural conditions, the presence of eastern mosquitofish resulted in an almost 70% reduction in the number of o.spring produced by A. iberus . The addition of extra, non-breeding males of A. iberus had no significant effect. YOY A. iberus from cages with eastern mosquitofish or extra males were significantly smaller (c. 1 mm, or 8% shorter) than those from cages without additional fish. Results for V. hispanica were not conclusive, as very few YOY were recovered. In contrast, eastern mosquitofish did not affect the survivorship of breeding adults of both native species.     

Use of a flooded salt marsh habitat by an endangered cyprinodontid fish (<Emphasis Type="Italic">Aphanius iberus</Emphasis>)

We report the first data on the use of occasionally inundated habitats in a Mediterranean coastal lagoon by the Spanish toothcarp (Aphanius iberus), a cyprinodontid fish in danger of extinction. During a flooding period, we sampled the fish population and the macroinvertebrate community in three contrasting habitats: mats of green algae, open water, and a habitat dominated by glasswort (Salicornia patula) that is occasionally inundated. The three habitats displayed strong variation in density and species composition of invertebrates in the water column and the benthos. In general, algal mats had higher invertebrate biomasses, but glasswort had higher diversity of organisms, in part of terrestrial origin. The density of toothcarp was very low in the open water. The habitat that is occasionally inundated (glasswort) significantly had the highest density of mature toothcarp, while immature fish were similarly abundant in the glasswort and algal mat habitats. Condition (weight–length relationship) and total food biomass in the gut contents of immature toothcarp was significantly higher in algal mats than in glasswort, whereas there were no such differences for mature fish. Therefore, the occasionally flooded habitat (glasswort) was positively selected by large mature toothcarp but seemed a disadvantageous habitat for immature individuals. Handling editor: L. Mauricio Bini.     

Size‐related and diel variations in microhabitat use of three endangered small fishes in a Mediterranean coastal stream

This study analysed the microhabitat use of three endangered fish species, Andalusian toothcarp Aphanius baeticus , Iberian loach Cobitis paludica and sand smelt Atherina boyeri , in a coastal stream stretch. Plastic minnow traps were set both during daytime and at night on the bottom and at the surface. Depth and presence of effective refuge were recorded for each trap. To assess size‐related changes in microhabitat use individuals of each species were classified in three size classes. The three species preferentially used bottom positions in the water column, though this behaviour was more evident in the case of Iberian loach. While large Iberian loach remained active at night Andalusian toothcarp and sand smelt were strongly diurnal, especially larger individuals. The three species showed a clear ontogenetic change in microhabitat preferences towards deeper waters. Small Andalusian toothcarp and medium‐sized Iberian loach used deeper microhabitat in the presence of refuge. Large Andalusian toothcarp consistently preferred exposed microhabitat at any time. Andalusian toothcarp using refuge were smaller at any time, while Iberian loach followed this pattern only at night. The differential vulnerability of these species to different predators (aerial and aquatic; diurnal and nocturnal) could explain the observed patterns in microhabitat use. Fish tended to co‐occur in microhabitats either due to habitat characteristics independently of species or due to species independently of habitat. Andalusian toothcarp segregated spatio‐temporally from sand smelt and Iberian loach, but these species occurred independently of each other. According to these co‐occurrence patterns, Andalusian toothcarp would be more sensitive than Iberian loach or sand smelt to interspecific interactions.     

Population and microhabitat effects of interspecific interactions on the endangered Andalusian toothcarp (A<Emphasis Type="Italic">phanius baeticus</Emphasis>)

The Andalusian toothcarp, Aphanius baeticus, is a critically endangered cyprinodontid species, with only nine known extant populations. Although not yet studied in the field, the distribution and abundance of Andalusian toothcarp are thought to be strongly influenced by interspecific interactions. We analysed the abundance and microhabitat use of Andalusian toothcarp in two water courses, one in which several other fish species occurred (sympatric site) and one hypersaline stream in which toothcarp was the only species present (allopatric site). Fish were sampled using plastic minnow traps and results were analysed separately for three size categories. Toothcarps were clearly more abundant in the allopatric population than in the sympatric one, though the difference was less apparent in the smallest size category. In coexistence with other species, toothcarp occupied shallower microhabitats, but in both sites in the absence of shelter fish selected deeper positions than in its absence. While in the sympatric site sheltered microhabitats were used predominately by small individuals, in the allopatric ones they were used by larger ones. Observed patterns strongly suggest that predation is the main mechanism involved in the differences in abundance and microhabitat use between sites. Our results confirm that the presence or absence of coexisting species is an important habitat feature for Andalusian toothcarp populations.     

Feeding ecology of the endangered Valencia toothcarp,Valencia hispanica (Actinopterygii: Valenciidae)

Patterns of food resource utilisation by Valencia toothcarp were studied in a small coastal lagoon in the Iberian Peninsula, its most northern population. Emphasis was placed on feeding activity, diet composition, seasonal and intraspecific variation in diet and feeding strategy. Important features of the overall feeding pattern of the Valencia toothcarp are decreased feeding activity during winter, concentration on benthic invertebrates and narrow dietary breadth, with a focus on gammarid amphipods. The feeding of V. hispanica was independent of seasonal variation in food availability, because its main prey were much the same throughout the year. There were no differences in seasonal niche width and niche overlap between seasons was high. There are also no differences in diets between sexes, although diet composition, niche width and niche overlap differ between juvenile and adult fish. The Valencia toothcarp population from Santes Creus lagoon was formed by specialist individuals, with narrow niche widths, that fed on four preferential prey types, but also consumed some occasional prey.     

Age, growth and reproduction of Aphanius iberus (Cuv. & Val., 1846) in the lower reaches of the Guadalquivir river (south-west Spain)

SUMMARY. 1. Age, growth and reproduction in an Atlantic population of the small fish, Aphanius iberus (Cuv. & Val., 1846), from the estuary of the Guadalquivir river were studied.
2. The growth period was from April to September and the annulus on the scales was formed in April.
3. The life-span was short with a winter age-structure of 95.9% 0+ fish, 3.9% 1+ and 0.2% 2+.
4. The fecundity of this stock, before the beginning of reproduction, is represented by the formula: Fec=0.907 TL (cm)^4.099. During the reproductive period 1+ females contained more, smaller eggs g⁻¹ of gonad than 0+ fish.
5. Males matured before females, but females were larger than males. The overall sex ratio did not differ from 1:1 but males dominated significantly during most of the spawning period.
6. Aphanius iberus spawned intermittently during the reproductive period. From April to July, 1+ group specimens (7–12 months old) reproduced. Their offspring (0+ group; 3–4 months old) reproduced from July to September. Very few of the 1+ group specimens survived to spawn the following year.
7. Mean gonadosomatic indices were much higher in the 1+ group than in the 0+ group and in females compared to males.
8. The loss of condition and the disappearance of the 1 + group during spawning, may indicate the cost of a prolonged high level of reproductive effort.
9. In this productive environment, the life history of Aphanius iberus is similar to that of Gambusia affinis (Baird & Girard, 1853) and Fundulus heteroclitus (Linnaeus) found in the same area.     

Possible reasons for the decline of two native toothcarps in the Iberian Peninsula: evidence of competition with the introduced Eastern mosquitofish

Interactions between adult individuals of the introduced Eastern mosquitofish Gambusia holbrooki and two native fish species to the Iberian Peninsula, the Iberian toothcarp Aphanius iberus and the Valencia toothcarp Valencia hispanica, were studied in mesocosm and laboratory experiments. Eastern mosquitofish always excluded both Valencia and Iberian toothcarp when the ratio introduced‐to‐native was at unity or favourable to the non‐native species. Food availability did not decrease significantly in the mesocosm experimental units. However, specimens of native species had a greater number of empty guts than those of Eastern mosquitofish at the end of the mesocosm experiment. Ethograms were constructed based on qualitative observations in aquaria, with a special emphasis on social behaviours, in particular agonistic (which ultimately were not observed between the species). Satiety (maximum prey number) and voracity (number of prey consumed per unit of time) of the three species were measured in aquaria. The Eastern mosquitofish achieved the highest foraging values (maximum prey = 11, at 11–12 prey min^?1), whereas Valencia toothcarp achieved the lowest values (maximum prey = 7, at 5–6 prey min^?1). The observed interactions between Eastern mosquitofish and the two native species are discussed.     

Temperature-Specific Competition between Invasive Mosquitofish and an Endangered Cyprinodontid Fish

Condition-specific competition is widespread in nature. Species inhabiting heterogeneous environments tend to differ in competitive abilities depending on environmental stressors. Interactions between these factors can allow coexistence of competing species, which may be particularly important between invasive and native species. Here, we examine the effects of temperature on competitive interactions between invasive mosquitofish, Gambusia holbrooki, and an endemic Iberian toothcarp, Aphanius iberus. We compare the tendency to approach heterospecifics and food capture rates between these two species, and examine differences between sexes and species in aggressive interactions, at three different temperatures (19, 24 and 29°C) in three laboratory experiments. Mosquitofish exhibit much more aggression than toothcarp. We show that mosquitofish have the capacity to competitively displace toothcarp through interference competition and this outcome is more likely at higher temperatures. We also show a reversal in the competitive hierarchy through reduced food capture rate by mosquitofish at lower temperatures and suggest that these two types of competition may act synergistically to deprive toothcarp of food at higher temperatures. Males of both species carry out more overtly aggressive acts than females, which is probably related to the marked sexual dimorphism and associated mating systems of these two species. Mosquitofish may thus impact heavily on toothcarp, and competition from mosquitofish, especially in warmer summer months, may lead to changes in abundance of the native species and displacement to non-preferred habitats. Globally increasing temperatures mean that highly invasive, warm-water mosquitofish may be able to colonize environments from which they are currently excluded through reduced physiological tolerance to low temperatures. Research into the effects of temperature on interactions between native and invasive species is thus of fundamental importance.     

Isolation and characterization of dinucleotide microsatellites in greater amberjack, <Emphasis Type="Italic">Seriola dumerili</Emphasis>

Thirteen nuclear-encoded dinucleotide microsatellites were characterized from a genomic DNA library of greater amberjack, Seriola dumerili. The microsatellites include 12 perfect-repeat motifs and one imperfect-repeat motif. The number of alleles at the 13 microsatellites among a sample of 29 fish ranged from 3 to 25; gene diversity (expected heterozygosity) ranged from 0.296 to 0.948, while observed heterozygosity ranged from 0.276 to 0.897. Following Bonferroni correction, genotypes at all 13 microsatellites fit expectations of Hardy-Weinberg equilibrium. One pairwise comparison of microsatellites deviated significantly from expectations of genotypic equilibrium, suggesting that these two microsatellites may be linked. Greater amberjack support commercial and recreational fisheries along both the Atlantic and Gulf coasts of the U.S. and represent a species with potential for worldwide aquaculture. The microsatellites developed will be useful for conservation and population genetic studies of ‘wild’ and domesticated populations of greater amberjack.     

黄鳝IgM的分离纯化及兔抗黄鳝IgM抗血清的制备

目的 分离纯化黄鳝血清免疫球蛋白,制备其兔抗血清,并检测抗血清的特异性。方法 用Protein A亲和层析的方法纯化黄鳝血清免疫球蛋白,通过SDS-聚丙烯酰胺凝胶电泳检测蛋白的纯度,免疫大耳白兔制备抗血清,利用免疫双扩散检测抗血清的效价,通过western blotting检测抗血清的特异性。结果 纯化了黄鳝血清免疫球蛋白,免疫双扩散法测定兔抗黄鳝免疫球蛋白血清效价为1∶32,western blotting结果显示抗血清具有很好的特异性。结论 成功纯化了黄鳝免疫球蛋白,制备了兔抗黄鳝IgM抗血清,为建立黄鳝的血清学检测系统奠定了基础。     

Length‐weight relationships in some populations and species of Iranian toothcarps

Length‐weight relationships were estimated for 16 populations of six Iranian toothcarp species. Differences between sexes were statistically significant for two of the species.     

The ultrastructure of amberjack (Seriola dumerilii) sperm

Scanning and transmission electron microscopy were used to investigate the fine structure of sperm of the Mediterranean amberjack Seriola dumerilii. Each spermatozoon has an ovoid head which lacks an acrosome, a short, irregularly-shaped midpiece and a long flagellar tail. The midpiece houses eight spherical mitochondria, which are separated from the axoneme by the cytoplasmic canal. The centrioles are arranged approximately at right angles to each other. The proximal centriole lies inside, and the distal centriole outside, the nuclear fossa. The flagellum is inserted eccentrically into the head and is tangential to the nucleus, so that the spermatozoon is asymmetrical. It contains the conventional 9 + 2 axoneme, shows intratubular differentiations in the A microtubules of doublets 1, 2, 5 and 6, and possesses one pair of lateral fins. On the basis of its ultrastructural organization, the amberjack sperm resembles type II sperm as defined previously, except for the presence of the proximal centriole inside the nuclear fossa. This could result from a partial rotation of the nucleus during spermiogenesis.     

Age and growth of an Iberian cyprinodont, Aphanius iberus (Cuv. & Val.), in its most northerly population

Age and growth of an Iberian cyprinodont, Aphanius iberus (Cuv. & Val.), in its most northerly population, La Rubina lagoon (Alt Empordà wetlands, NE Spain), was studied. The age groups for this Mediterranean population (O +, 1 + and 2 +) agree with those reported for the Atlantic population (R. Guadalquivir marshes), in the southern limit of the species distribution in the Iberian peninsula. Differences in age structure between these populations and the one previously studied in La Tancada lagoon (R. Ebro delta marshes) can be attributed to age estimation bias. Male A. iberus data appear to fit similarly to a Gompertz growth function and to a von Bertalanffy growth function, but L _x, was clearly underestimated. A Gompertz growth function was not a good fit for females, perhaps because female growth is clearly faster and less attenuated than male growth. The life history and growth pattern ofthis species is similar to that in other cyprinodontiform fishes, typified by a short longevity. The growth model of this species does not seem to fit types I and II of Sebens's classification, which are characteristic of fish.     

Chromosomal polymorphism associated with Robertsonian fusion in Seriola dumerili (Risso, 1810) (Pisces: Carangidae)

The diploid numbers 2 n = 48, and 2 n = 47 have been determined for the greater amberjack, Seriola dumerili. A chromosome polymorphism due to Robertsonian fusion is present in this species. A simple sex-determining mechanism has not been observed.     

Circadian self-feeding rhythms in greater amberjack Seriola dumerili (Risso)

In the present study, 10 greater amberjack Seriola dumerili held individually were given free access to self-feeder, and trigger actuations were continuously monitored. Most (80%) of greater amberjack developed stable self-feeding activity within 1 week. The fish was a rigidly diurnal feeder under a 12L:12D cycle, with a feeding peak of 1–3 h occurring just after the onset of lights. Under constant conditions, all 10 individual fish exhibited free-running self-feeding rhythms, which persisted for 43 days without a sign of damping out. As far as is known, this seems to be the longest record of free-running behavioural rhythms in fishes. Except one fish free-ran at a period length (τ) of 25·2 h, τ of free-running self-feeding rhythms in the other nine fish was shorter than 24 h, ranging from 20·0 h to 21·5 h. In addition, phase transients of feeding activity were observed in response to the advancement of lights on. It is concluded that feeding activity in greater amberjack is mediated by endogenous circadian oscillators.     

Origin of a Spanish population of Fundulus heteroclitus inferred by cytochrome b sequence analysis

Fundulus heteroclitus in the estuary of the Guadalquivir River in southern Spain competes with a native killifish, Aphanius iberus . Cytochrome b sequence analysis shows that the Spanish individuals are derived from the northern of two possible American populations of F. heteroclitus     

Dynamics and predicted decline of Anguillicola crassus infection in European eels, Anguilla anguilla, in Neusiedler See, Austria

The eel population in Neusiedler See has been maintained by regular massive stocking since 1958. After the establishment of the National Park Neusiedler See-Seewinkel in 1993, eel stocking was prohibited and the population, together with the specific parasites of eels, was predicted to decline to extinction within 10 years. This investigation was undertaken to document the decline and extinction of the Anguillicola crassus population in eels. From 1994 to 2001, 720 eels were collected from two sites in the lake. Prevalence and abundance of A. crassus were lower in spring than in summer and autumn and larger eels harboured more parasites than smaller ones. Neither year of study nor sampling site were correlated with parasite infection levels. No significant trend in the population parameters of A. crassus was detected over the 8 years of the survey. This suggested that there had been no significant decline in the eel population. This suggestion was confirmed by investigations of the fishery, which also found evidence of regular illegal stocking. The stability of the A. crassus population over the past decade seems to reflect the lack of change in eel population density. No mass mortalities of eels occurred over the period despite the many similarities between Neusiedler See and Lake Balaton in Hungary. Differences in eel size, eel diet and the lack of large-scale insecticide use are discussed as possible explanations for the absence of eel mass mortalities in Neusiedler See.     

Regional variation in otolith Sr:Ca ratios of African longfinned eel Anguilla mossambica and mottled eel Anguilla marmorata: a challenge to the classic tool for reconstructing migratory histories of fishes

Otolith Sr:Ca ratios of the African longfinned eel Anguilla mossambica and giant mottled eel Anguilla marmorata from nine freshwater sites in four rivers of South Africa were analysed to reconstruct their migratory life histories between freshwater and saltwater habitats. For A. mossambica, the Sr:Ca ratios in the otolith edge differed significantly among rivers and had large effect sizes, but did not differ among sites within a river. Otolith Sr:Ca ratios did not differ among rivers for A. marmorata. When rivers were pooled, the edge Sr:Ca ratios of A. mossambica were not significantly different from those of A. marmorata. According to the river-specific critical Sr:Ca ratio distinguishing freshwater from saltwater residence, most A. mossambica and A. marmorata had saltwater habitat experience after settlement in fresh water. This was primarily during their elver stage or early in the yellow eel stage. During the middle and late yellow eel stage, freshwater residency was preferred and only sporadic visits were made to saltwater habitats. The data also suggest that regional variations in otolith Sr:Ca ratios affect the critical Sr:Ca value and are a challenge for the reconstruction of migratory life histories that should be explicitly considered to avoid bias and uncertainty.     

The swimbladder nematode Anguillicola crassus in the European eel Anguilla anguilla and the Japanese eel Anguilla japonica: differences in susceptibility and immunity between a recently colonized host and the original host

The swimbladder nematode Anguillicola crassus originates from Asia where it is a parasite of the Japanese eel Anguilla japonica. After its introduction to Europe about 25 years ago, the parasite spread rapidly within the indigenous populations of the European eel Anguilla anguilla and subsequently the prevalence and mean intensity appeared to stabilize. Under experimental and aquaculture conditions the na?ve new host appears to be more susceptible to A. crassus compared to the original host. Both eel species develop a immune response against A. crassus. The antibody response is well characterized for the European eel, but poorly characterized for the Japanese eel. It remains unclear if antibodies have any protective function against A. crassus. Encapsulation of larvae of A. crassus can be observed in naturally infected European eels. However, encapsulation of larvae following experimental infection has not been detected in European eels, but only in Japanese eels. Reinfection experiments and intraperitoneal injection of A. crassus homogenates failed to demonstrate the development of acquired immunity in European eels. Immunization with irradiated third stage larvae provided preliminary evidence for acquired immunity against A. crassus in the Japanese eel, but not in the European eel.