Pathology of pentastomid infections (Sebekia mississippiensis) in fish

Differential pathogenesis was observed in two species of fish naturally infected with the pentastome Sebekia mississippiensis. Mosquitofish (Gambusia affinis) showed a mild inflammatory response to developing nymphs, whereas swordtails (Xiphophorus helleri) had an extensive granulomatous inflammatory reaction with accompanying hemorrhage, myositis, and myodegeneration. This suggested that certain species of tropical fish reared in the southeastern United States may be at risk to potentially harmful infections with this parasite.     

Phenotypic variation among populations of Atherinops affinis(Atherinopsidae) with insights from a geometric morphometric analysis

Morphological character variation was examined in Atherinops affinis , a temperate marine silverside with a broad geographic range and presumed limited powers of dispersal. Populations of this species were sampled from three California mainland sites, one Channel Island site and one site in the upper Gulf of California. A geometric morphometric analysis yielded higher resolution in the assessment of phenotypic divergence among the four Pacific coast populations than either body measurement or meristic analysis, and it showed that most of the shape variation among these populations occurs in the head region and body depth of the fish. All three analyses supported the hypothesis that populations of A. affinis from central and southern California coastal waters and from Santa Catalina Island are morphologically distinct from each other; the Santa Catalina Island population was found to be the most divergent. On the basis of meristic characters alone, the population of A. affinis from the upper Gulf of California was different from A. affinis populations along the Pacific coast of California. The analyses revealed variation in several morphological characters, e.g . body depth and meristics, known to vary in association with environmental conditions. Given that A. affinis appears to have low among‐population genetic variation, this species may be phenotypically plastic in response to the environmental conditions of the habitat of each population.     

Predator-driven phenotypic diversification in Gambusia affinis

Predation is heterogeneously distributed across space and time, and is presumed to represent a major source of evolutionary diversification. In fishes, fast-starts--sudden, high-energy swimming bursts--are often important in avoiding capture during a predator strike. Thus, in the presence of predators, we might expect evolution of morphological features that facilitate increased fast-start speed. We tested this hypothesis using populations of western mosquitofish (Gambusia affinis) that differed in level of predation by piscivorous fish. Body morphology of G. affinis males, females, and juveniles diverged in a consistent manner between predatory environments. Fish collected from predator populations exhibited a larger caudal region, smaller head, more elongate body, and a posterior, ventral position of the eye relative to fish from predator-free populations. Divergence in body shape largely matched a priori predictions based on biomechanical principles, and was evident across space (multiple populations) and time (multiple years). We measured maximum burst-swimming speed for male mosquitofish and found that individuals from predator populations produced faster bursts than fish from predator-free populations (about 20% faster). Biomechanical models of fish swimming and intrapopulation morphology-speed correlations suggested that body shape differences were largely responsible for enhanced locomotor performance in fish from predator populations. Morphological differences also persisted in offspring raised in a common laboratory environment, suggesting a heritable component to the observed morphological divergence. Taken together, these results strongly support the hypothesis that divergent selection between predator regimes has produced the observed phenotypic differences among populations of G. affinis. Based on biomechanical principles and recent findings in other species, it appears that the general ecomorphological model described in this paper will apply for many aquatic taxa, and provide insight into the role of predators in shaping the body form of prey organisms.     

长江黄州江段长须黄颡鱼肠道内寄生棘头虫的生态研究

解剖检查了 133尾捕自长江黄州江段的长须黄颡鱼 ,发现寄主感染长江丽棘虫的感染率为 4 8.9% ,感染强度为 5 .4 (虫 /尾 ) ,平均密度为 2 .6 (虫 /尾 ) ,感染鲇异棘虫的感染率为 2 1.8% ,感染强度为 5 .5 (虫 /尾 ) ,平均密度为1.2 (虫 /尾 ) ,两种棘头虫在长须黄颡鱼种群中均为聚集分布 ;当两种棘头虫共同寄生在宿主肠道内时 ,其感染强度和单独感染时相比没有显著差异 ,但是 ,各自的生态位宽度均变小 ;两种棘头虫的正关联关系显著。     

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.      

Conservation genetics of peripheral populations of the mygalomorph spider Atypus affinis (Atypidae) in northern Europe

Genetic diversity and differentiation were studied in peripheral populations of the recently rediscovered purse-web spider Atypus affinis in Denmark and Sweden using allozyme electrophoresis. Because of the very narrow environmental niche exploited by this species, only a limited number of potential habitats are available. Furthermore, fragmentation has reduced the number and size of potential habitats within the last century. The level of genetic diversity in A. affinis was intermediate compared with other nonsocial spiders, but low compared with invertebrates in general. Significant genetic differentiation was found within distances of only 1-10 km with FST estimates ranging from 0.020 to 0.075. Within distances of 30-60 km FST ranged from 0.081 to 0.312. Hierarchical FST revealed that genetic variability was partitioned at 89.8% within populations, 9.5% among populations within regions and only 0.7% among the four main regions in Denmark and Sweden. Comparing the result of the genetic analysis with the life history of A. affinis, it is concluded that the level of successful dispersal is low, and that the species has not recently reinvaded northern Europe but prevailed undiscovered for several decades. Finally, it is suggested that the genetic scenario found for A. affinis might represent that for a wide range of other arthropods with similar life history characteristics.     

Population biology of two helminth parasites of flatfishes from the Atlantic coast of Morocco

On the Atlantic Moroccan coast, two species of pleuronectiform fish coexist, wedge sole ( Citharus linguatula ) a temperate species, and spotted flounder ( Dicohgoglossa cuneata ) a tropical one. These two species are the definitive host for Bothriocephalus andresi and Acanthocephaloïdes propinquus , respectively. A negative binomial fits the dispersion of B. andresi in the population of C. linguatula . The fish become parasitized between their first and third year, while still immature, with the highest abundances in the third year. After the fish become ichthyopagous, the level of infection drops drastically. We postulate that copepods are the sole source of infection. The presence of B. andresi in both Atlantic and Mediterranean populations of C. linguatula shows that the parasite follows the host during its migration along the Mediterranean coasts.
The prevalence of A. propinquus remains above 50% as a consequence of the large numbers of amphipods included in the diet of D. cuneata , regardless of the age of the fish or the season. The amphipods, Phtisica marina and Pariambus typicus are an important food and represent potential intermediate hosts for A. propinquus . The population dynamics of A. propinquus on the Atlantic Moroccan coasts are similar to those observed in parasite populations of Gobius niger in the Gulf of Lion (French Mediterranean). The observation of B. andresi and A. propinquus in both Moroccan Atlantic and Mediterranean fishes highlights the problem of the evolution of these parasite populations during the colonization of the Mediterranean by the hosts.     

Temporal variation in fish community structure in a newly created wetland lake (Lake Agmon) in Israel

Lake Agmon was constructed in summer 1994 in the northern part of the drained Lake Hula swamp, as part of the Hula Reclamation Project. One of the main goals of the project was to attract aquatic and semi- aquatic birds to the area as a basis for planned eco-tourism and one of the main concerns of the project was the potential for increased proliferation of mosquitoes (including vector species of malarial parasites). There was a perceived need, therefore, to establish and maintain a suitable fish community. This present study documents the developments in the fish community in Lake Agmon between May 1995 and December 1996. The lake was initially stocked with two fish species, Tilapia zillii and Gambusia affinis, to control mosquitoes and to provide suitable small- bodied forage species for piscivorous birds. Subsequent stocking also included Oreochromis aureus, and Cyprinus carpio. Additional species were established by immigration from the Jordan River. Relatively large species ( e.g., Clarias gariepinus and C. carpio) flowed into the lake as eggs or juveniles, whereas the smaller species ( e.g., Hemigrammocapoeta nana, Pseudophoxinus kervillei and Aphanius mento) entered the lake as adults. In the first year, eight fish species were found in Lake Agmon: T. zillii, G. affinis, C. gariepinus, C. carpio, Capoeta damascina, P. kervillei, Acanthobrama lissneri and H. nana. Of these, T. zillii, G. affinis and H. nana were dominant, though the relative abundance of H. nana was very low in spring, and increased during summer. In the second year, O. aureus, A. mento and Anguilla anguilla also occurred in the lake. The density of P. kervillei increased, in comparison with the previous year. The relative proportions of juvenile and adult fish also changed in the second year. A high percentage of young T. zillii was found during the first spring, decreasing in the summer and autumn. The proportion of juveniles of both G. affinnis and H. nana was very low during the first year, but increased during the second. These results indicate that the fish community of Lake Agmon had not stabilized by the end of 1996 and that further changes in relative abundances, and species, age and sex compositions should be expected.     

Homozygosity and Heterozygosity in three Populations of Rivulus marmoratus

Rivulus marmoratus is a self-fertilizing hermaphroditic fish found in the tropical Atlantic as populations of homozygous clones, with the exception of a single site in Belize where male fish are abundant and heterozygosity is the norm. The presence of male fish apparently leads to outcrossing and heterozygosity, but males have been found in limited numbers in other populations which are homozygous. DNA fingerprinting now reveals that the Belize population has remained heterozygous, with a high proportion of males (20–25%), for several years. In addition, two newly discovered populations with a lower percentage of males (1–2%) are reported from the Bahamas and Honduras. One of these populations (Bahamas) consists of homozygous clones, while the other (Honduras) displays a limited proportion of heterozygosity. The Honduras population is only the second outcrossing population known in this species, and the limited heterozygosity seen here may reflect the lower proportion of males.     

The Floral Biology of Tricyrtis affinis Makino (Liliaceae)

Abstract The floral biology of Tricyrtis affinis was investigated and compared with that of four species of Tricyrtis which had been reported by the author. The flower opens for two days and is protandrous as in T. latifolia, T. flava , and T. ohsumiensis. The primary pollinators of T. affinis were Bombus diversus diversus and Amegilla sp., which were not different from those of the previous species although the shape and the color of the T. affinis flower are somewhat different from the others. The whole perianth of T. affinis absorbs UV light fairly well, and the large purple spotted area near the base absorbs it markedly well. The UV absorption pattern of the T. affinis flower is similar to that of T. latifolia. T. affinis is also self-compatible, like the others, and seeds obtained by self-pollination germinated well. Pollination of T. affinis is characterized by a refined system.     

Zoogeography of the shorefish fauna of Clipperton Atoll

One hundred and fifteen species of fishes (14 oceanic, plus 101 shore and nearshore species) are known from Clipperton Island, a small, remote coral atoll in the tropical eastern Pacific (TEP). This fish fauna includes only 14% of the region's shallow-water species, and also is depauperate relative to the fish faunas of other isolated tropical islands. The island's isolation, small size, reduced habitat diversity, and oceanic environment contribute to this paucity of species.Fifty-two species at Clipperton can be identified as TEP; these include 37 widespread species, six species shared only with the Revillagigedo Islands [the nearest (950 km) offshore shoals], and eight endemic to Clipperton. Endemics species apparently have a mix of west and east Pacific origins. Sixty-three species are transpacific; they include three new records (of Naso surgeonfishes) that maybe vagrants recruited > 4,000 km from Oceania.Clipperton is situated at the juncture between the TEP and Oceania. Its fish fauna contains about equal numbers of TEP and transpacific species. This faunal structure reflects the relative influence of surface currents from Oceania and the TEP. Although most of Clipperton's transpacific shorefishes are widespread in eastern Oceania, the Clipperton fauna has specific affinities to the fauna of the Line Islands, which are located within the main eastbound current from Oceania. Clipperton may therefore be a major stepping stone for dispersal between Oceania and the remainder of the TEP. About 50% of the non-oceanic, tropical transpacific fishes occur there, and at least 75 % of those species apparently have resident populations at the island.     

Ontogenetic diet shifts in Roeboides affinis with morphological comparisons

Fishes of the characid genus Roeboides are documented as lepidophagous, but the degree of specialization on scales varies between species. This study examines ontogenetic changes in morphology and diet of Roeboides dayi and Roeboides affinis from Venezuela. Juveniles of both species feed on microcrustacea and insects during the wet season, when availability of these resources is greatest. As aquatic habitat decreases during the dry season, insect and microcrustacea availability decreases and fish densities increase. As the fish densities increase, scale consumption becomes more profitable. Interspecific differences in the degree of specialization of the teeth and jaws was associated with the degree of scale feeding. Adult R. dayi consumed scales in approximately equal proportions to insects. Adult R. affinis consumes approximately 100% scales, and has more specialized head morphology than R. dayi.     

Helminth-modified pulmonary immune response protects mice from allergen-induced airway hyperresponsiveness

It has been shown that the presence of certain helminth infections in humans, including schistosomes, may reduce the propensity to develop allergies in infected populations. Using a mouse model of schistosome worm vs worm + egg infection, our objective was to dissect the mechanisms underlying the inverse relationship between helminth infections and allergies. We have demonstrated that conventional Schistosoma mansoni egg-laying male and female worm infection of mice exacerbates airway hyperresponsiveness. In contrast, mice infected with only schistosome male worms, precluding egg production, were protected from OVA-induced airway hyperresponsiveness. Worm-infected mice developed a novel modified type 2 cytokine response in the lungs, with elevated allergen-specific IL-4 and IL-13 but reduced IL-5, and increased IL-10. Although schistosome worm-only infection is a laboratory model, these data illustrate the complexity of schistosome modulation of host immunity by the worm vs egg stages of this helminth, with the potential of infections to aggravate or suppress allergic pulmonary inflammation. Thus, infection of mice with a human parasitic worm can result in reduced airway inflammation in response to a model allergen.     

Feeding ecology of pelagic fish species in the Gulf of Riga (Baltic Sea): the importance of changes in the zooplankton community

The feeding ecology of four pelagic fish species was studied in relation to their prey availability in the Gulf of Riga (Baltic Sea) during the summer 1999-2006. The zooplankton community was dominated by the cladoceran Bosmina longispina, rotifers Keratella cochlearis and K. quadrata and the copepod Eurytemora affinis, with the highest interannual variability in abundance recorded for B. longispina. The last influenced the diet of adult sprat Sprattus sprattus, juvenile smelt Osmerus eperlanus and three-spined stickleback Gasterosteus aculeatus as these were strongly selecting for B. longispina. The fish feeding activity did not match the abundance dynamics of their preferred prey, suggesting that fishes may switch to consume other prey in case the preferred diet was limited. A considerable dietary overlap indicated high potential competition between pelagic fish species. While herring Clupea harengus membras and G. aculeatus were relying on very different food, the diets of young O. eperlanus and G. aculeatus were very similar. Interannual variability in zooplankton composition and abundance significantly affected the diet composition of fishes, but those changes were insufficient to exert a consistent influence upon fish feeding activity and total amounts of zooplankton consumed.     

The application of RAPD markers in stock discrimination of the four-wing flyingfish, Hirundichthys affinis in the central western Atlantic

The polymerase chain reaction–random amplified polymorphic DNA (PCR–RAPD) technique was used to examine genetic variability and population structuring in the four-wing flyingfish, Hirundichthys affinis within the central western Atlantic. Three random decamer primers and pairs of these primers were used to amplify nuclear DNA from 360 fish sampled from six populations (at five locations) across the region. A total of 58 polymorphic RAPD markers were identified, 20 of which were population-specific and six of which were subregional or stock-specific markers. Cluster analysis of similarity indices indicated the presence of three genetically distinct subregional stocks located in the eastern Caribbean, southern Netherlands Antilles and Brazil, respectively. Estimates of gene diversity (φ) and gene flow ( Nm ) are consistent with this three-stock hypothesis. Furthermore, partially restricted gene flow was apparent among spatially and temporally separate sampled populations within the eastern Caribbean subregional stock, indicating the possible presence of different spawning groups. These results are entirely consistent with those obtained from PCR–RFLP analysis of the mtDNA D-loop in the same fish, indicating the presence of barriers to dispersal and interbreeding in both sexes. We conclude that the PCR–RAPD technique is suitable for determining population stock structure in this species and that a three-stock approach to managing H. affinis within the central western Atlantic would be appropriate.     

Interactions of pelagic cnidarians and ctenophores with fish: a review

Medusae, siphonophores and ctenophores (here grouped as `pelagic coelenterates') interact with fish in several ways. Some interactions are detrimental to fish populations, such as predation by gelatinous species on pelagic eggs and larvae of fish, the potential competition for prey among pelagic coelenterates and fish larvae and zooplanktivorous fish species, and pelagic coelenterates serving as intermediate hosts for fish parasites. Other interactions are positive for fish, such as predation by fish on gelatinous species and commensal associations among fish and pelagic coelenterates. The interactions range from beneficial for the gelatinous species (food, parasite removal), to negative (predation on them). We review existing information and present new data on these topics. Although such interactions have been documented frequently, the significance to either fish or pelagic coelenterate populations is poorly understood. The effects of pelagic coelenterates on fish populations are of particular interest because of the great importance of fisheries to the global economy. As fishing pressures mount, it becomes increasingly important to understand how they may influence the balance between pelagic coelenterates and fish.     

Adaptation to sea level rise: does local adaptation influence the demography of coastal fish populations?

This study compared the growth of two western mosquitofish Gambusia affinis populations that were previously demonstrated to have genetic adaptations that increased survival under lethal salinity exposures. The objective was to evaluate how genetic adaptations to lethal salinity stress affect population demography when exposed to sublethal salinity stress. Results indicate that chronic salinity exposure had a generally negative impact on population size, but fish originating from one of the two populations established with fish from a brackish site exhibited an increase in population size. Saltwater intrusion seems to result in reduced population size for most populations. Some populations inhabiting more saline sites, however, may develop localized adaptations, mitigating the consequences of increased salinity on population productivity.     

The effects of Myxobolus cerebralis myxospore dose on triactinomyxon production and biology of Tubifex tubifex from two geographic regions

The aquatic oligochaete Tubifex tubifex is an obligate host of Myxobolus cerebralis, the causative agent of salmonid whirling disease. Tubifex tubifex can become infected by ingesting myxospores of M. cerebralis that have been released into sediments upon death and decomposition of infected salmonids. Infected worms release triactinomyxons into the water column that then infect salmonids. How the dose of myxospores ingested by T. tubifex influences parasite proliferation and the worm host are not well understood. Using replicated laboratory experiments, we examined how differing doses of myxospores (50, 500, 1,000 per worm) influenced triactinomyxon production and biomass, abundance, and individual weight of 2 geographically distinct populations of T. tubifex. Worm populations produced differing numbers of triactinomyxons, but, within a population, the production did not differ among myxospore doses. At the lowest myxospore dose, 1 worm population produced 45 times more triactinomyxons than myxospores received, whereas the other produced only 6 times more triactinomyxons than myxospores. Moreover, total T. tubifex biomass, abundance, and individual weight were lower among worms receiving myxospores than in myxospore-free controls. Thus, T. tubifex populations differ in ability to support the replication of M. cerebralis, and infection has measurable consequences on fitness of the worm host. These results suggest that variability in whirling disease severity observed in wild salmonid populations may partially be attributed to differences in T. tubifex populations.     

Sealworm (Pseudoterranova decipiens) transmission to fish trawled from Hvaler, Oslofjord, Norway

Demersal fish were sampled over 3 years to describe sealworm Pseudoterranova decipiens infection levels in relation to the size of a local colony of common seals Phoca vitulina in Hvaler, Oslofjord, Norway. More than 2000 fish were examined for worms, and five fish species were found to be infected, cod Gadus morhua , four-bearded rockling Enchelyopus cimbrius , plaice Pleuronectes platessa , long rough dab Hippoglossoides platessoides and dab Limanda limanda. A detailed analysis of worm accumulation in cod, the only infected species present in large enough numbers, shows a net decrease in worm transmission following the phocine distemper virus epizootic which killed two-thirds of the seals in Hvaler in 1988.     

Spatiotemporal and gender‐specific parasitism in two species of gobiid fish

Parasitism is considered a major selective force in natural host populations. Infections can decrease host condition and vigour, and potentially influence, for example, host population dynamics and behavior such as mate choice. We studied parasite infections of two common marine fish species, the sand goby (Pomatoschistus minutus) and the common goby (Pomatoschistus microps), in the brackish water Northern Baltic Sea. We were particularly interested in the occurrence of parasite taxa located in central sensory organs, such as eyes, potentially affecting fish behavior and mate choice. We found that both fish species harbored parasite communities dominated by taxa transmitted to fish through aquatic invertebrates. Infections also showed significant spatiotemporal variation. Trematodes in the eyes were very few in some locations, but infection levels were higher among females than males, suggesting differences in exposure or resistance between the sexes. To test between these hypotheses, we experimentally exposed male and female sand gobies to infection with the eye fluke Diplostomum pseudospathaceum. These trials showed that the fish became readily infected and females had higher parasite numbers, supporting higher susceptibility of females. Eye fluke infections also caused high cataract intensities among the fish in the wild. Our results demonstrate the potential of these parasites to influence host condition and visual abilities, which may have significant implications for survival and mate choice in goby populations.