Fecundity of whitefish (Coregonus lavaretus) during the eu-and oligotrophication of Lake Constance

About 20 ovaries of the whitefish 'Blaufelchen' ( Coregonus lavaretus L.) of Lake Constance (Bodensee) were collected annually from 1964-1991. Absolute and relative fecundity peaked in the early 1980s, lagging about 2 years behind the maximum of total-P in the water (during the circulation period). Out of the biological time-series of Lake Constance, whitefish fecundity is the only one known to follow the phosphorus curve, and this may be the first time-series documented case of parallel trend reversal in the trophic state of a lake and fish biology. It is concluded that fish fecundity serves, at best, as an unspecific monitor of the overall well-being of the fish.     

A comparative assessment of temporal variation in diet of powan, Coregonus lavaretus (L.), from Loch Lomond and Loch Eck, Scotland, U.K.

Stomach contents of powan caught throughout the year from Loch Lomond and Loch Eck were examined. Adult powan in Loch Lomond fed mainly on planktonic Cladocera, switching to benthic food during December-April. Bosmina coregoni was the principal planktonic food with Daphnia hyalina an important late summer and autumn prey. Loch Eck powan fed throughout the year on chironomid larvae and Pisidium spp. from the benthos and ingested large amounts of non-food material. Mean dry weights of food in stomachs were correlated with water temperature in Loch Lomond but not in Loch Eck and were higher in powan from Loch Eck over most of the year.     

Radioactive strontium (85Sr) in marking whitefish [Coregonus lavaretus (L.)] larvae and the dispersal of larvae from river to sea

Anadromous whitefish [ Coregonus lavaretus (L.)] yolk-sac larvae were marked with a radioactive strontium isotope, ⁸⁵Sr. Before marking the method was tested in accumulation-elimination tests using various strontium concentrations. The first-phase effective half-life of ⁸⁵Sr in yolk-sac larvae was 4 days. The mean ⁸⁵Sr radioactivity was 81 Bq per larva at the day of release and the half-life of the slow component was 51 days, so the strontium label was easily detected up to 60 days after marking. The larvae were released into the River Simojoki about 12 km upstream from the river mouth and recaptured from early May to the end of July. Marked larvae were found at the river mouth 12–13 days after release, while the last marked fish in the river were found at 16 days. It is likely that all leave the river within 2 to 3 weeks post-hatching. Two months after marking some larvae had attained a distance of 10 km from the river mouth.     

Regional variations in the outer retina of atherinomorpha (Beloniformes,Atheriniformes, Cyprinodontiformes: Teleostei): photoreceptors,cone patterns,and cone densities

The outer retinae of adults of 13 atherinomorph species, representing nine different families, were examined by both light and electron microscopy. The retinae were investigated with respect to photoreceptor types, cone densities, and cone patterns. All data were composed to eye maps. This procedure allows an interspecific comparison of the regional differences within the outer retina among these shallow-water fish. Furthermore, for a more detailed pattern analysis nitro-blue tetrazolium chloride- (NBT)-stainings in the retina of Melanotaenia maccullochi are presented. Apart from rods, eight morphologically different cone types could be identified: short, intermediate, and long single cones, double cones (equal and unequal), triple cones (triangular and linear), and in Ameca splendens one quadruple cone. Dimensions and occurrence of photoreceptors vary among the respective species and within the retinal regions. In the light-adapted state, the cones are arranged in highly ordered mosaics. Five different cone tessellation types were found: row patterns, twisted row patterns, square patterns, pentagonal patterns, and, exclusively in Belone belone, a hexagonal pattern. In Melanotaenia maccullochi the different spectral photoreceptor classes correspond well with the distribution of morphological photoreceptor classes within the mosaic. Double cone density maxima together with a highly ordered cone arrangement usually occur in the nasal and/or ventral to ventrotemporal retina. In most of the species that were examined these high-density regions are presumed to process visual stimuli from the assumed main directions of vision, which mainly depend on feeding behavior and predator pressure. Our findings are discussed with respect to the variable behavioral and visual ecology and phylogeny of the respective species.     

Human‐induced changes in the reproductive traits of Lake Constance common whitefish (Coregonus lavaretus)

Size‐selective fishery harvest leads to phenotypic changes in fish reproductive traits. When these changes represent an evolutionary response of a stock, they may have severe consequences for future stock dynamics and yields. In freshwater ecosystems, reproductive traits may also be affected by other human impacts such as changes in system productivity. The present study uses regression analysis to evaluate the impacts of changes in lake trophy and of an intensive size‐selective harvest over several decades on the reproductive traits of common whitefish in Lake Constance between 1963 and 1999. Fecundity was strongly linked to lake trophy but was also related to the calendar year, suggesting an evolutionary response to size‐selective harvest and to massive stocking of the lake with hatchery‐reared larvae. The present study is an example of how fish reproductive traits are influenced by the combined action of various human impacts: changes in system productivity, size‐selective harvest and massive stocking.     

Outer retinal fine structure of the garfish Belone belone (L.) (Belonidae, Teleostei) during light and dark adaptation – photoreceptors, cone patterns and densities

In the present EM study, we investigate the retina of Belone belone , a visually-orientated marine predator living close to the water surface. In the duplex retina, four morphologically different cone types are observed: unequal and equal double cones, long single cones and triple cones. In the light-adapted state, five different cone patterns occur: row, twisted row, square, pentagonal and hexagonal patterns. High double cone densities are found ventro-nasally, ventro-temporally and dorso-temporally. Throughout the retina the double cone/single cone ratio is 2 : 1, in the ventral part, however, a 1 : 1 ratio occurs. In the vitreous body we found a curtain-like intraocular septum dividing the retina into two morphologically different regions. In most areas of the dark-adapted retina the cone patterns are absent at the ellipsoid level, with long single cones standing more vitreally in the light path than double cones. The mosaics are retained, however, in the outer nuclear layer. Typical dark adaptation, i.e. the retinomotor movements of the retinal pigment epithelium and photoreceptors in response to the dark adaptation (light change) is not present in the peripheral ventral and parts of the central ventral area. In both regions we found a twisted row pattern of cones having a vitreal position. The findings are discussed with respect to the photic habitat and feeding habits of this species.     

Different growth trends of whitefish (Coregonus lavaretus) forms in the northern Baltic Sea

The sea growth of two whitefish forms, anadromous (Coregonus lavaretus lavaretus) and sea‐spawning (Coregonus lavaretus widegreni), was analysed using samples collected from the commercial sea catch in the Gulf of Bothnia (GoB) in the northern Baltic Sea during 1998–2014. In the GoB area, these two forms are possible to identify because the gill‐raker number and size at maturity vary between forms. The growth rate of the forms is linked to their feeding area. Sea‐spawning whitefish, which has a feeding migration near its home site, was shorter in the northern GoB (66°N–64°N) at the ages of 3–11 than those in the southern GoB (64°N–60°30′N). In the data, most whitefish were caught with gill nets in the GoB. The mesh sizes of gill nets capturing the anadromous form were mostly 35–45 mm, while those capturing the sea‐spawning form were <35 mm in the northern GoB. It is likely that the different growth trends for small and large whitefish were connected with differences in their recruitment for fishing. The length of anadromous females at the age of four sea years increased significantly, but the length of six‐year‐old anadromous female whitefish decreased over the catch years from 1998–2014. In contrast, the length of slow‐growing sea‐spawning whitefish of six years or older increased significantly in relation to the catch year in the gill‐net catch. The increase in the growth of young age groups in both forms was probably associated with the increasing temperature and the low fishing pressure on small fish. The decreasing age at capture for both forms and the depression of the mean size of old anadromous whitefish are signs of high fishing pressure with a high gill‐net effort that selectively removes the largest and oldest individuals of both forms.     

Clasping structure in the double cone of the retina of the turtle (Gyoclemys reevesii)

Summary The double cone of the turtle retina was reconstructed three-dimensionally from electron micrographs of 400 serial sections. Cytoplasm of the accessory cone extends bilaterally to surround the principal cone incompletely. The cytoplasmic extensions are 0.1 m in width and 2 m in length at their longest portions. They arise at approximately the median portion of the ellipsoid (consisting of mitochondria) and terminate at the level of the outer limiting membrane. The possible function of these extensions as a clasping structure is discussed.     

Fine structure and development of the retina of the grenadier anchovy Coilia nasus (Engraulididae, Clupeiformes)

A study of the morphogenesis of the grenadier anchovy retina was undertaken using light and electron microscopy. Five developmental stages from prelarvae 3 days after fertilization to adult fish were studied. In addition to the general morphology of the eye and retina, special emphasis was given to the development of the photoreceptors and pigment epithelium (PE). The earliest retinae showing structural features indicative of a functioning eye are pure cone retinae composed of rows of alternating long and short cones forming a transient, tesselated pattern. At this stage there is a conventional PE containing melanin. In older stages cone rows are separated by the newly formed rods and by PE wedges filled with diffusely reflecting guanine crystallites. The findings are compared with the retinae of other engraulidids and with the development of teleost retinae in general. Moreover, the observed structural changes are discussed with respect to the photic habitat conditions of these anadromous fish that move between coastal waters, estuary, and river.     

Morphological variation among populations of Aphanius fasciatus Nardo, 1827 (Teleostei, Cyprinodontidae) from the Mediterranean

The amount of osteological variation among 11 Italian killifish Aphanius fasciatus populations was examined by the univariate and multivariate analysis of 40 morphometric and meristic variables of the skull and vertebral column. Populations were sampled in three geographically distinct areas (the Adriatic, Sardinia and Sicily). The statistical analysis confirmed that several populations were well differentiated. In particular, discriminant analysis revealed a strong discriminating power of the morphometric variables. Morphometrics of the vertebrae, bony elements of the pharyngeal jaws, supraoccipital and parasphenoid were the most important in discriminating populations. The dendrogram obtained by UPGMA cluster analysis shows the separation of the south-eastern Sicilian populations, that of the Sardinian populations and that of the central-northern Sicilian plus Adriatic populations, as well as the isolation of the Sicilian population from Pantano Viruca and of the Sardinian populations from Pauli Figu from all the others. The significance of the observed differentiation pattern is discussed.     

Genetic admixture of burbot (Teleostei: Lota lota) in Lake Constance from two European glacial refugia

The burbot, Lota lota, is the only freshwater species of the codfish family and has a Holarctic distribution. Pleistocene glaciations caused significant geographical differentiation in the past, but its life history characterized by winter spawning migrations over large distances is likely to homogenize populations by contemporary gene flow. We investigated the population genetic structure of 541 burbots from Lake Constance and adjacent Rhine and Danube tributaries in Europe using the entire mitochondrial DNA (mtDNA) control region and 11 microsatellites. Microsatellites revealed considerable population divergence (F(ST) = 0.26) and evidenced recent bottlenecks in two Central European rivers. In accordance to previous evidence two main phylogeographic lineages (Atlantic and Danubian) were found co-occurring at similar frequencies in Lake Constance, where they currently undergo random mating as indicated by microsatellites. The Danubian lineage contributed only a small proportion to the lake's mtDNA diversity, and probably expanded within the lake shortly after its formation approximately 10,000-15,000 BP. The larger Atlantic haplotype diversity suggested a population expansion older than the lake itself. Levels of admixture at microsatellite loci were less obvious due to their high variability, and coalescence methods were used to estimate past admixture proportions. Our results reinforce a model of a two-step colonization of Europe by burbot from an ancestral Danubian refuge, and confirm the persistence of a secondary Atlantic refuge, as proposed to exist for other freshwater fish. We conclude that the present-day burbot population in Lake Constance bears the genetic signature of both contemporary gene flow and historical separation events.     

Life histories of the powan,Coregonus lavaretus (L.) (Salmonidae,Coregoninae) of Loch Lomond and Loch Eck

Four aspects of the life histories of the two populations of powan Coregonus lavaretus (L.) in Scotland are described: growth (Eck powan are shorter and with greater year to year variance than Lomond); sexual maturation (Eck powan mature younger, but at similar weight to Lomond); spawning (timing in Eck varies, but is consistent in Lomond); and recruitment/mortality (fecundity, sex ratios, and mortality also vary in the short term). Short term differences between the physiological ecology of the populations can be ascribed to the size and topography of the lochs. Long term differences are more difficult to account for, and are more important in that they may signal changes in sustainability. Conservation of powan must be considered in terms of their synecological relationships, not in isolation.     

Photoreceptors and cone patterns in the retina of the smelt Osmerus eperlanus (L.) (Osmeridae: Teleostei)

The outer retina of the smelt Osmerus eperlanus, a visually orientated plankton feeder, of Lake Hiidenvesi (Finland), was examined using both light and transmission electron microscopy. Apart from rods, six morphologically different cone photoreceptor types were identified: short single cones, long single cones, unequal/equal double cones and triple cones (triangular and linear variety). Additionally, in the dorsal region, multiple cone arrangements consisting of up to five members occur. Long single cones and triple cones were observed only sporadically throughout the retina. The incidence of short single cones as a regular element of the cone mosaic is restricted to the ventrotemporal area. The dominant pattern in the Osmerus retina is a pure or a twisted row pattern occurring in all regions. Ventrotemporally, however, square patterns were found as well. The highest cone densities occur in the peripheral ventrotemporal retina. These results indicate that the ventrotemporal region plays an important role in the vision of the smelt. The findings are discussed with respect to the photic habitat conditions and behavioural ecology of the smelt in Lake Hiidenvesi.     

Unusual cell organelles during spermiogenesis in two species of gobies (Gobiidae,Teleostei)

Summary Testes of Lesuerigobius friesii and Gobius bucchichi were studied in adult reproductive fish. During the onset of spermatid development, a peculiar system of alternating rough (RER) and smooth (SER) endoplasmic reticular tubules form rings distally to the cell nucleus. The RER tubules are seen to possess up to 12 ribosomes in cross-section, whereas the SER are strongly electron-dense. Nanotubules connect these stacks of tubules to the developing head and tail of the sperm. With ripening of the sperm these tubules disintegrate within the excessive cytoplasm. It seems likely that these are special forms of Macro-Golgi System that possibly provide protamines for the developing sperm.     

Sequence analysis of the mitochondrial DNA control region of ciscoes (genus Coregonus): taxonomic implications for the Great Lakes species flock

Sequence variation in the control region (D-loop) of the mitochondrial DNA (mtDNA) was examined to assess the genetic distinctiveness of the shortjaw cisco ( Coregonus zenithicus ). Individuals from within the Great Lakes Basin as well as inland lakes outside the basin were sampled. DNA fragments containing the entire D-loop were amplified by PCR from specimens of C. zenithicus and the related species C. artedi , C. hoyi , C. kiyi , and C. clupeaformis . DNA sequence analysis revealed high similarity within and among species and shared polymorphism for length variants. Based on this analysis, the shortjaw cisco is not genetically distinct from other cisco species.     

Osteology and relationships of the genus Spaniodon (Teleostei, Salmoniformes) from the Santonian (Upper Cretaceous) of Lebanon

The genus Spaniodon is decribed in detail. Contrary to previous authors, we have only recognized two species, S. elongatus and S. latus . Spaniodon shows the synapomorphies of clupeocephalans, protacanthopterygians and salmoniforms. Its relationships among salmoniforms are still undecided, although it could be closely related to the Osmeroidei. The main character that supports this grouping is the dermal part of the mesethmoid formed by the partial fusion of a pair of lateral dermethmoids, whereas the rostral is absent. These conclusions are also supported by a global phylogenetic study of the teleosts.     

PERMANENT GENETIC RESOURCES: Isolation and characterization of microsatellite loci from the Arctic cisco (Coregonus autumnalis)

Eight polymorphic microsatellite loci were isolated and characterized for the Arctic cisco, Coregonus autumnalis. Loci were evaluated in 21 samples from the Colville River subsistence fishery. The number of alleles per locus ranged from two to 18. Observed heterozygosity of loci varied from 0.10 to 1.00, and expected heterozygosity ranged from 0.09 to 0.92. All eight microsatellite markers were in Hardy-Weinberg equilibrium. The loci presented here will be useful in describing population structure and exploring populations of origin for Arctic cisco.     

A new pearleye (Teleostei,Aulopiformes) species from the Oligocene of Romania

A new pearleye species of the alepisauroid family Scopelarchidae, Scopelarchoides neamticus sp. nov., is described herein based on two specimens from the Oligocene Lower Dysodilic Shales Formation, cropping out in the Pietricica Mountain, Romanian Eastern Carpathians. The new species described herein exhibits a unique combination of features (including head length about 25% of SL; coracoid remarkably expanded; both preorbital and postorbital lengths larger than orbit diameter; 50 or 51 vertebrae; dorsal fin with nine or ten rays; anal-fin with 28 rays; length of anal fin base about 30% of SL; preanal distance almost 60% of SL; pelvic fin insertion located just under the second dorsal fin ray; pectoral fins only slightly longer than pelvic fins; caudal fin with 19 principal rays plus 14 upper and 13 lower procurrent rays) that justifies its recognition as a new species of the genus Scopelarchoides. Both morphological and meristic features suggest a certain degree of similarity between S. neamticus sp. nov. and the extant species Scopelarchoides signifer. The fossils of the new Oligocene species described herein represent the oldest known skeletal record of Scopelarchidae.