Motile iridophores of a freshwater goby,Odontobutis obscura

Summary Reflecting chromatophores in the dermis of the skin of a freshwater goby, Odontobutis obscura, are of an iridophore type. These chromatophores contain numerous reflecting platelets, which are similar to those in iridophores of other fish and amphibian species. It was found that these iridophores are motile, i.e., these cells respond to certain stimuli with translocation of the platelets within the cells. K⁺ ions induced dispersion of the platelets in excised scale preparations, but not in excised scales from chemically denervated fish. Norepinephrine and melatonin also induced dispersion of the platelets. Alpha-MSH was effective in aggregating these organelles into the centrospheres of the cells. The conclusions reached are: (1) iridophores of O. obscura are motile; (2) the movement of the iridophores is under nervous and hormonal control.     

Catchment-Scale Conservation Units Identified for the Threatened Yarra Pygmy Perch (Nannoperca obscura) in Highly Modified River Systems

Habitat fragmentation caused by human activities alters metapopulation dynamics and decreases biological connectivity through reduced migration and gene flow, leading to lowered levels of population genetic diversity and to local extinctions. The threatened Yarra pygmy perch, Nannoperca obscura, is a poor disperser found in small, isolated populations in wetlands and streams of southeastern Australia. Modifications to natural flow regimes in anthropogenically-impacted river systems have recently reduced the amount of habitat for this species and likely further limited its opportunity to disperse. We employed highly resolving microsatellite DNA markers to assess genetic variation, population structure and the spatial scale that dispersal takes place across the distribution of this freshwater fish and used this information to identify conservation units for management. The levels of genetic variation found for N. obscura are amongst the lowest reported for a fish species (mean heterozygosity of 0.318 and mean allelic richness of 1.92). We identified very strong population genetic structure, nil to little evidence of recent migration among demes and a minimum of 11 units for conservation management, hierarchically nested within four major genetic lineages. A combination of spatial analytical methods revealed hierarchical genetic structure corresponding with catchment boundaries and also demonstrated significant isolation by riverine distance. Our findings have implications for the national recovery plan of this species by demonstrating that N. obscura populations should be managed at a catchment level and highlighting the need to restore habitat and avoid further alteration of the natural hydrology.     

Larval development of a gobiid fish,Odontohutis obscura obscura in comparison with that ofO. o. interrupta and ofO. platycephala

Larval development ofOdontobutis obscura obscura, reared withArtemia sp. andLimnodrilus sp. for about two months, was observed in a room maintained at 20±0.5°C. The development was classified into nine nominal stages, and was compared with that ofO. o. interrupta and ofO. platycephala. The size and shape of the eggs and the development of this species are similar to those ofO. o. interrupta andO. platycephala. From the juvenile stage,O. obscura is distinguishable fromO. platycephala by the appearance of dark bands on the body located in the same position as in adults.O. o. interrupta is also distinguished fromO. o. obscura in the juvenile stage by the presence of melanophores on the dorsal and ventral sides of the caudal peduncle. The anal fin fold ofO. obscura is higher than the dorsal fin fold, but the two folds are equal in height inO. platycephala. O. obscura has a well-developed air bladder and swims high in the water at the feeding stage.O. platycephala has a poorly developed air bladder and swims on the bottom. Xanthophores are observed at an earlier stage and more strongly developed inO. obscura than inO. platycephala. Growth rate is faster inO. obscura than inO. platycephala. O. obscura spawns at a smaller body size thanO. platycephala. InO. o. obscura, the arrangement of cephalic pit organs is completed at 14 mm SL. InO. o. interrupta, this arrangement is completed at the same time or a little later than inO. o. obscura. The infraorbital and verticalantorbital pit lines ofO. platycephala, which are separated in the adults, are connected until the juveniles measure about 30 mm SL. These pit lines are connected even in the adults ofO. o. obscura andinterrupta. InO. platycephala, the sensory canals are first formed behind the eyes, then dorso-anterior to the eyes, then at the posterior edge of the preopercles and finally anterior to the eyes. Postocular canals begin to form in individuals more than 20 mm SL. All individuals ofO. o. interrupta more than 70 mm SL have postocular canals.O. o. obscura has no sensory canals throughout life. The differences in growth rate, body size at spawning, and the time of completion of the cephalic lateral line system suggest paedomorphosis in the three taxa studied here.     

Genetic diversity and population structure of bocachico Prochilodus magdalenae (Pisces,Prochilodontidae) in the Magdalena River basin and its tributaries,Colombia

Prochilodus magdalenae is an endemic freshwater fish that occurs in the Magdalena, Sinú and Atrato hydrographic basins. It has an important economic role and is a food resource for the artisanal fishing communities. Its socioeconomic importance contrasts with the current status of its fisheries, where stocks are being depleted. Considering its importance and lack of information on its genetic structure, we used seven microsatellite markers to assess the genetic structure of wild populations of P. magdalenae. The genetic diversity was assessed and the population genetic structure was estimated through Fst, analysis of molecular variance and Bayesian analysis. A total of 290 alleles were found in all loci throughout all population. The high polymorphism contrasts with the levels of observed heterozygosity (Ho = 0.276), which are the lowest values recorded for the family. We found three populations of bocachico coexisting throughout the studied system, contradicting the hypothesis that freshwater migratory fish form panmictic populations. These results on the genetic structure of P. magdalenae constitute tools for a better understanding of the behavior and biology of this species, contributing to fish management and conservation programs.     

Ichthyofaunal survey of rivers within Ewekoro cement manufacturing operational areas

A total of 298 fish specimens belonging to seven families were caught during ichthyoplanktonic survey of three rivers within the Ewekoro cement facility catchment area located in southwestern Nigeria. The highest numbers of specimens were caught from Alaguntan (37.0%) and Elebute (36.6%) rivers while 28.9% of the fish samples were collected from Itori River. The fish population and species diversity recorded in the catchment rivers were significantly lower (p < 0.05) than comparative catches from Ewekoro River located about 30 km downstream of the factory operational area. The food items ingested by the specimens across the seasons in the catchment rivers revealed obvious differences in diet with some degree of overlap in the fish trophic preferences. However, the omnivorous species dominated the catches in each of the rivers, irrespective of season. Categorization of the fish specimens based on habitat-related adaptive physiology showed that a significant number of the fish from Alaguntan and Itori Rivers have accessory respiratory organs. The four species with accessory respiratory organs were Polypterus senegalus Curv., Clarias gariepinus C. & V., Ctenopoma kingslayae Gun. and Channa obscura Smith. Of the 12 fish species recorded in the Ewekoro cement facility catchment rivers, only P. senegalus, C. gariepinus, C. obscura and Oreochromis niloticus (Trew.) are valuable food fishes in southwestern Nigeria.     

Divergence in selection of host species and plant parts among populations of a phytophagous insect

The diversification of phytophagous insects is often attributed to diverging processes of host plant specialization onto different, often closely related, host plants. Some insect clades have diversified by specializing not only on different plant species but also on different plant parts of the same hosts. This is the case in Greya moths (Prodoxidae) where both Greya obscura and G. politella are tightly linked to host plants of the genus Lithophragma (Saxifragaceae). We assess how these species differ in their choice of plants and use of plant parts. Previous work showed that strong local host specialization in G. politella is mediated by floral scent variation among Lithophragma species. Here, we identify geographic variation in host plant use in the close relative G. obscura, relate the emerging patterns to previous studies of geographic variation in host use in G. politella and evaluate potential processes underlying the variation among and within species. First, we show that G. obscura also uses floral chemistry to locate hosts but that additional plant cues must be involved in deciding whether to oviposit on a plant, because females did not discriminate against chemically different host species in no-choice trials. We also found that, although all known populations of G. politella oviposit only in flowers, all G. obscura populations examined here distributed their eggs among both floral and scape tissues both in the field and in laboratory experiments. The distribution of eggs among plant parts, however, varied among moth populations, and also depended on the Lithophragma species they attacked. Together, these results show the potential for phytophagous insect species and populations to diverge in use of plant parts as part of the process of speciation and adaptation. These two layers of specialization enhance the potential for subsequent diversification in phytophagous insect lineages.     

Trichodinidae in commercial fish in South America

Ciliates of the family Trichodinidae are protozoan parasites of importance for fish farming in South America, given that at high infestation levels, they cause significant mortality among farmed fish. Although data on economic losses due to parasitosis are not available for South America, mortality outbreaks correlated to trichodinids are very common in the tilapia production chain, especially in Brazil, the largest aquaculture chain in the country. In Brazil in the past, trichodinids were considered only as Trichodina sp. Today, they have been better studied and identified taxonomically in wild and farmed fish. However, in other countries in South America, trichodinids continue to be described only as Trichodina sp. This review presents the history of occurrences of trichodinids in fish of interest in South America, highlighting 15 new species that have been described in three genera in Brazil, along with information on parasite-host-environment relationships, diagnostic methods and treatments. The occurrence of parasitic ciliates must be correlated with farming conditions such as stress factors, water quality, seasonality, age and host immunity to elucidate the critical points of each production system. Furthermore, for tropical fish, studies on treatment against trichodinid species are needed to provide support for approval of antiparasitic medications for use in fish farming. However, it is recommended that the production sector use intensive production systems that are more sustainable, with biosafety protocols, to increase production and productivity.     

Redescription of a brooding nemertine,Cyanophthalma obscura (Schultze) gen. et comb.n., with observations on its biology and discussion of the species of Prostomatella and related taxa*†

A new genus, Cyanophthalma, is erected with the type species Tetrastemma obscura Schultze, 1851. Cyanophthalma obscura is transferred from Prostomatella and is redescribed from observations of more than 300 living specimens and serial sections of 59 specimens from the northeast coast of North America. Comparison is made with serial sections of C. obscura from the Baltic and with serially sectioned specimens of three other described species of Prostomatella. Two of these, P. enteroplecta and P. merula, do not fit either genus and are provisionally placed in the aggregate genus Tetrastemma, whose present diagnosis they do fit. Prostomatella remains with only its type species, P. arenicola. Amphiporus cordiceps is also transferred to Cyanophthalma. Some of the characters that form the basis for classifying Monostilifera are assessed for phylogenetic significance. Cyanophthalma obscura in Nova Scotia lives in salt marshes. Young are brooded through the winter while ice covers most of the marsh.     

Variation in stable isotope (δO and δC) signatures in the sagittal otolith carbonate of king threadfin, Polydactylus macrochir across northern Australia reveals multifaceted stock structure

Otoliths of king threadfin, Polydactylus macrochir were collected from 2007 to 2009 at nine locations across northern Australia representing most of their distributional range and areas where fisheries are active. Measurement of the stable isotope ratios of δ¹⁸O and δ¹³C in the sagittal otolith carbonate from assemblages of P. macrochir revealed location-specific signatures and indicated that adult fish sampled from representative sites across their range were significantly different. The significant differences in the isotopic signatures of P. macrochir demonstrated that population subdivision is evident and there is unlikely to be substantial movement of fish among these distinct adult assemblages. The stable isotopic signatures for the fish from the different locations were persistent through time, and therefore it could be concluded that they comprise separate stocks for many of the purposes of fisheries management. The spatial separation of these populations indicates a complex stock structure across northern Australia with stocks of P. macrochir associated with large coastal beaches and embayments on a fine spatial scale. These results indicate that in order to achieve optimal fisheries management, the current spatial management arrangements need to be reviewed, particularly the potential for localised depletion of stocks on small spatial scales. This study has provided further evidence that measurement of the stable isotopes ratios in teleost sagittal otolith carbonate can be a valuable tool in the delineation of fishable stocks or fishery management units of adult fish and that widely distributed fish can nonetheless show strong localised population structure.     

Intensive aquaculture selects for increased virulence and interference competition in bacteria

Although increased disease severity driven by intensive farming practices is problematic in food production, the role of evolutionary change in disease is not well understood in these environments. Experiments on parasite evolution are traditionally conducted using laboratory models, often unrelated to economically important systems. We compared how the virulence, growth and competitive ability of a globally important fish pathogen, Flavobacterium columnare, change under intensive aquaculture. We characterized bacterial isolates from disease outbreaks at fish farms during 2003–2010, and compared F. columnare populations in inlet water and outlet water of a fish farm during the 2010 outbreak. Our data suggest that the farming environment may select for bacterial strains that have high virulence at both long and short time scales, and it seems that these strains have also evolved increased ability for interference competition. Our results are consistent with the suggestion that selection pressures at fish farms can cause rapid changes in pathogen populations, which are likely to have long-lasting evolutionary effects on pathogen virulence. A better understanding of these evolutionary effects will be vital in prevention and control of disease outbreaks to secure food production.     

Temporal Genetic Variance and Propagule-Driven Genetic Structure Characterize Naturalized Rainbow Trout (Oncorhynchus mykiss) from a Patagonian Lake Impacted by Trout Farming

Knowledge about the genetic underpinnings of invasions—a theme addressed by invasion genetics as a discipline—is still scarce amid well documented ecological impacts of non-native species on ecosystems of Patagonia in South America. One of the most invasive species in Patagonia’s freshwater systems and elsewhere is rainbow trout (Oncorhynchus mykiss). This species was introduced to Chile during the early twentieth century for stocking and promoting recreational fishing; during the late twentieth century was reintroduced for farming purposes and is now naturalized. We used population- and individual-based inference from single nucleotide polymorphisms (SNPs) to illuminate three objectives related to the establishment and naturalization of Rainbow Trout in Lake Llanquihue. This lake has been intensively used for trout farming during the last three decades. Our results emanate from samples collected from five inlet streams over two seasons, winter and spring. First, we found that significant intra- population (temporal) genetic variance was greater than inter-population (spatial) genetic variance, downplaying the importance of spatial divergence during the process of naturalization. Allele frequency differences between cohorts, consistent with variation in fish length between spring and winter collections, might explain temporal genetic differences. Second, individual-based Bayesian clustering suggested that genetic structure within Lake Llanquihue was largely driven by putative farm propagules found at one single stream during spring, but not in winter. This suggests that farm broodstock might migrate upstream to breed during spring at that particular stream. It is unclear whether interbreeding has occurred between “pure” naturalized and farm trout in this and other streams. Third, estimates of the annual number of breeders (N _b) were below 73 in half of the collections, suggestive of genetically small and recently founded populations that might experience substantial genetic drift. Our results reinforce the notion that naturalized trout originated recently from a small yet genetically diverse source and that farm propagules might have played a significant role in the invasion of Rainbow Trout within a single lake with intensive trout farming. Our results also argue for proficient mitigation measures that include management of escapes and strategies to minimize unintentional releases from farm facilities.     

Genetic diversity and differentiation of the Korean starry flounder (Platichthys stellatus) between and within cultured stocks and wild populations inferred from microsatellite DNA analysis

The Korean starry flounder, Platichthys stellatus, is economically valuable coastal resident fish species. However, the annual catch of this fish has fluctuated and suffered major declines in Korea. We examined the genetic diversity and population structure for four wild populations and three hatchery stocks of Korean starry flounder to protect its genetic integrity using nine microsatellites. A group of 339 genotypes belonging to seven populations were screened. High degrees of polymorphism at the microsatellite loci were observed within both the wild and hatchery populations. Compared to the wild populations, genetic changes, including reduced genetic diversity and highly significant differentiation, have occurred in cultured stocks. Significant population differentiation was also observed in wild starry flounder populations. Similar degrees of inbreeding and significant Hardy–Weinberg equilibrium deviations were detected in both the wild and the hatchery populations. The genetic connectivity pattern identified four distinct metapopulations of starry flounder in Korea by clustering in the phylogenetic tree, Bayesian analyses, molecular variance analysis, PCA and multidimensional scaling analysis. A pattern of isolation-by-distance was not significant. This genetic differentiation may be the result of the co-effects of various factors, such as historic dispersal, local environment or anthropogenic activities. These results provide useful information for the genetic monitoring of P. stellatus hatchery stocks, for the genetic improvement of this species by selective breeding and for designing suitable management guidelines for the conservation of this species.     

Review of bees as guests in termite nests,with a new record of the communal bee, <Emphasis Type="Italic">Gaesochira obscura</Emphasis> (Smith, 1879) (Hymenoptera,Apidae), in nests of <Emphasis Type="Italic">Anoplotermes banksi</Emphasis> Emerson, 1925 (Isoptera,Termitidae, Apicotermitinae)

Associations between bees and termites are documented infrequently, but records are available for bee species ranging in behavior from solitary to highly eusocial. The subtribe Meliponina (stingless bees) is the most common bee group reported in termite nests, and, for some species, the occupancy of termite nests may be obligatory. The records of solitary bees nesting within termite nests include species of the tribes Emphorini, Centridini, Megachilini, and Paracolletini. Most of these bees can probably nest in other substrates, and their relationships with termite nests are presumably opportunistic. This study provides a review of published records of bees as guests in termite nests, and also describes the aggregation of nests of Gaesochira obscura within one nest of Anoplotermes banksi in Brazilian Amazonia. One termite nest contained at least ten nest entrances of G. obscura, with burrows 4–6 mm in diameter and about 10 cm long. Each burrow ended in brood cells in different stages of food provisioning and larval development. As commonly reported for other associations of this nature, there was no connection between the tunnels of bees and those of termites. This record adds important data on the biology of A. banksi. Because this is a single record, it is impossible to classify G. obscura either as a termitophile or termitariophile; this species may be opportunistic in relation to nesting substrate.     

Molecular Evolution of P Transposable Elements in the Genus Drosophila. II. The obscura Species Group

A phylogenetic analysis of P transposable elements in the Drosophila obscura species group is described. Multiple P sequences from each of 10 species were obtained using PCR primers that flank a conserved region of exon 2 of the transposase gene. In general, the P element phylogeny is congruent with the species phylogeny, indicating that the dominant mode of transmission has been vertical, from generation to generation. One manifestation of this is the distinction of P elements from the Old World obscura and subobscura subgroups from those of the New World affinis subgroup. However, the overall distribution of elements within the obscura species group is not congruent with the phylogenetic relationships of the species themselves. There are at least four distinct subfamilies of P elements, which differ in sequence from each other by as much as 34%, and some individual species carry sequences belonging to different subfamilies. P sequences from D. bifasciata are particularly interesting. These sequences belong to two subfamilies and both are distinct from all other P elements identified in this survey. Several mechanisms are postulated to be involved in determining phylogenetic relationships among P elements in the obscura group. In addition to vertical transmission, these include retention of ancestral polymorphisms and horizontal transfer by an unknown mating-independent mechanism.     

饵料中添加维生素C对非洲鲶鱼幼鱼生长和营养利用效率的影响

通过研究非洲鲶鱼(Clarias gariepinus)的生长和营养利用来探讨其维生素C的需求量。平均体重为6.02g±0.4g的鲶鱼幼鱼被放置在60cm×45cm×45cm的玻璃缸中,每缸10条鱼,每个处理设3个重复。5组饵料中粗蛋白的含量均为40%,并测定且其基础饲料中维生素C的含量。在第1、2、3、4和5组中,其饵料中维生素C多聚磷酸酯的添加量依次为0(对照)、50、100,150和200mg/kg。每天用这些饵料喂鱼两次,分别在格林尼治时间的9:00和16:00喂食。鲶鱼幼鱼每周称重一次,以便进行统计分析。通过其生长和营养利用效率进行生物学评估。结果表明,特定生长率、食物转换率、蛋白质效率和食物效率在所有组中彼此间都有显著差异。综合所有实验结果看,添加维生素C多聚磷酸酯150mg/kg的第4组,幼鱼的生长和营养利用效率最好。     

Emergy analysis for the environmental sustainability of an inshore fish farming system

The emergy concept was used to evaluate the environmental sustainability of the rearing process of Gilthead Sea Bream (Sparus aurata) in an inshore fish farming system in Gulf of La Spezia (Italy, Northwestern Mediterranean). Emergy is defined as the available energy of one kind previously used up directly and indirectly to make a product or service. The indices for the examined fish farm calculated from the emergy evaluation were compared with those of three other systems producing fishes: two intensive fish farming systems producing, respectively, salmons (Salmo salar) and tilapia (Tilapia mariae), the third system producing again S. aurata but in a semi-natural extensive manner. The emergy evaluation showed that the rearing of fishes in a sheltered area of Mediterranean Sea imposes a large stress on the environment. The greatest contributions to the emergy needed for production were due to fingerlings purchased and goods and services provided that are two external, non-renewable inputs to the system. The strong dependence of external contributions and the relative inability at exploiting local natural resources affect strongly the level of environmental sustainability of the productive process.     

Bacterial vaccines for fish

Vaccination of fish for the prevention of specific bacterial diseases afffecting commercially reared fish species has had a significant impact on this industry. Almost all of the vaccines available at this time are bacterins or formalin-inactivated whole cell suspensions, some with adjuvants. The first vaccines to be successfully commercialized were those against Vibrio anguillarum, Vibrio ordalii, and Yersinia ruckeri in the late 1970s. Developed initially for the salmonid industry, these bacterins are now routinely used worldwide on many species of fish. Though in some areas salmon farming has flourished without the use of these vaccines, in most areas they have been essential to the economic viability of aquaculture operations. Vaccines against Vibrio salmonicida, a pathogen of salmonids, Aeromonas salmonicida, a pathogen of salmonids and carp, and Edwardsiella ictaluri, a pathogen of channel catfish have also been commercialized and are in widespread use. A number of other bacterins have been the subject of research and some of them may eventually be available. Though a bacterin against Vibrio parahaemolyticus, a pathogen affecting species of fish reared in warmwater has been successfully tested, as have bacterins against Aeromonas hydrophila and Edwardsiella tarda, the serologic heterogeneity of these groups of organisms make it unlikely that widely utilizable vaccines will be available in the near future. Those pathogens that appear to be serologically more homogeneous, including Flexibacter columnaris, Pasteurella piscicida and Streptococcus species affecting fish, will likely end up in commercially available bacterins in the not too distant future. The use of a new generation of adjuvants in conjunction with automated injection methods could result in vaccines that will protect against diseases that conventional methods may not be successful against, such as bacterial kidney disease (BKD) caused by Renibacterium salmoninarum.     

Nuclear and mitochondrial ribosomal RNA variability in the obscura group of Drosophila

Parts of 28S (nuclear) and 12S (mitochondrial) ribosomal RNA of Palearctic, Nearctic and African species of the obscura group have been sequenced by the direct method of sequencing. Rates of nucleotide substitutions in both molecules were compared. The nucleotide divergence is higher in the mitochondrial rRNA. Average distances of species taken in pairwise were compared to results obtained with the melanogaster subgroup: the divergence of nuclear rRNA appears lower, that of the mtDNA higher whereas genetic distances (allozymes) and sncDNA distances are similar. Noticeable variability of evolutionary rates can be observed even in low taxonomical levels. Phylogenetic trees for the obscura group are in general agreement with those obtained with other characters.     

Host selection and host switching in <Emphasis Type="Italic">Gymnolophus obscura</Emphasis> – a symbiotic ophiuroid associated with feather stars (Crinoidea: Comatulida)

The present paper aims to assess the host-selectivity and host-switching behaviour of the comatulid associated ophiuroid Gymnolohpus obscura. The relationships between size-structure, distribution and infestation characteristics of G. obscura were assessed among all available feather star species in the Bay of Nhatrang, Vietnam, together with the frequency of injuries among symbiont size classes. Our data show that despite the fairly wide host distribution ranges, not all of them are equally infested by G. obscura, likely because of host morphology, size and location on the substrate. The most preferred hosts were the comatulids Comaster nobilis and Comanthus parvicirrus, which were preferably infested by larger symbionts. The highest frequency of injuries was found in symbionts with disks ranging from 0.6 to1 cm in diameter, tracing a host-to-host migration behaviour leading to a sharp fall in abundance in the 1.1–1.5 cm size class. Our results suggest that host-switching (either between the same or among different host species) is a characteristic behaviour of G. obscura, driven by either intraspecific competition and/or by searching for more favourable trophic or protective conditions.