Genetic differentiation among populations of the shortfinned eel Anguilla australis from East Australia and New Zealand

Variability at seven microsatellite loci was used to survey the genetic population structure of the shortfinned eel Anguilla australis . Samples were collected from six estuaries along the east coast of Australia and from three estuaries around New Zealand. Hierarchical analysis of molecular variance of the five loci with good fit to Hardy–Weinberg genotypic proportions detected highly significant differences among samples ( F _ST= 0·016, P < 0·001). The fixation index between countries ( F _CT= 0·012, P < 0·001) was more than double the index among samples within countries ( F _SC= 0·005, P < 0·05). An unweighted pair-group method with arithmetic mean (UPGMA) tree also supported the separation of Australian and New Zealand populations, as did assignment tests, which correctly assigned 80 and 84% of the individuals to Australia and New Zealand, respectively. Isolation-by-distance appeared among samples overall ( r = 0·807, P < 0·001), but not among samples within countries ( r = 0·027, P > 0·05 in Australia; r = 0·762, P > 0·05 in New Zealand). These findings indicate that populations of A. australis in East Australia and in New Zealand may be reproductively isolated from one another. Genetic differentiation among populations of A. australis was two- to 10-fold higher than that among populations of other temperate eels in the North Atlantic Ocean, suggesting that two group of A. australis may reflect sub-species. Anguilla australis in the two countries have different genetic structures and thus require separate management. Genetic isolation between Australian and New Zealand populations indicates that juveniles recruit independently into these two regions from geographically or temporally isolated spawning areas.     

Genetic Structure of Chum Salmon (Oncorhynchus keta) Populations in the Lower Columbia River: Are Chum Salmon in Cascade Tributaries Remnant Populations?

The lower Columbia River drainage once supported a run of over a million chum salmon. By the late 1950s, the run had decreased to often a few hundred fish. With the exception of Grays River near the coast and an aggregation of chum salmon spawning in creeks and the main stem near Bonneville Dam in the Columbia Gorge, most populations were thought to be extinct. However, chum salmon consistently return in low numbers to tributaries originating in the Cascade Range: the Cowlitz, Lewis, and Washougal rivers. To assess whether Cascade spawners were strays or remnants of former populations, chum salmon from the Coastal, Cascade and Gorge ecoregional zones were characterized at 17 microsatellite loci. Significant heterogeneity in genotype distributions was detected between zones and collections formed regional groups in a neighbor-joining tree. Cascade collections had higher allelic richness and private alleles, and the Cowlitz River supported genetically divergent fall and summer runs, the only summer chum salmon run extant in the Columbia River drainage. We propose that chum salmon in the Cascade zone are remnants of original populations. We attribute the divergence between zonal groups to diverse ecological conditions in each zone, which promoted regional genetic adaptation, and to genetic drift experienced in small populations.     

Population genetic structure and effective population size of ayu (Plecoglossus altivelis), an amphidromous fish

The temporal and spatial population genetic structure of ayu Plecoglossus altivelis (Salmoniformes: Plecoglossidae), an amphidromous fish, was examined using analysis of variation at six microsatellite DNA loci. Intracohort genetic diversities, as measured by the number of alleles and heterozygosity, were similar among six cohorts (2001–2006) within a population (Nezugaseki River), with the mean number of alleles per cohort ranging from 11·0 to 12·5 and the expected heterozygosity ranging from 0·74 to 0·77. Intrapopulational genetic diversities were also similar across the three studied populations along the 50 km coast, with the mean number of alleles and the expected heterozygosity ranging from 11·33 to 11·67 and from 0·75 to 0·76, respectively. The authors observed only one significant difference in pair-wise population differentiation ( F _ST-value) between the cohorts within a population and among three populations. Estimates of the effective population size ( N _e) based on maximum-likelihood method yielded small values (ranging from 94·8 to 135·5), whereas census population size ranged from c. 4800 to 24 000. As a result, the ratio of annual effective population sizes to census population size ( N _e/ N ) ranged from 0·004 to 0·023. These estimates of N _e/ N agree more closely with estimates for marine fishes than that of the larger estimates for freshwater fishes. The present study suggests that ayu which is highly fecund and shows low survival during the early life stages is also characterized by having low value of N _e/ N , similar to marine species with a pelagic life cycle.     

Bimodal run distribution in a northern population of sockeye salmon (Oncorhynchus nerka): life history and genetic analysis on a temporal scale

Life history variation and genetic differentiation were analysed in sockeye salmon in Klukshu River, Yukon Canada over 7 years (1994-2000). Sockeye salmon return to the Klukshu River in two distinct runs, with a small 'early run' in June-August, and a larger 'late run' in August-September. A maximum likelihood test for clusters indicated that the return frequency distribution was bimodal in all the years analysed. Life history differences (fork length, sex ratio, age at maturity, fresh- and saltwater residency times) were found between the early and late runs; however, inconsistent patterns suggest that environmental effects outweigh, or strongly interact with, genetic effects for the life history characters evaluated. Analysis of variation at eight microsatellite loci showed that the early and late runs are genetically differentiated in all years examined (exact test). FST estimates between runs within years were significantly greater than zero (range: 0.018-0.041) for all years except one (0.004). The genetic variance explained by early vs. late runs (2.27%) was twice the variance among years (1.16%) based on analysis of molecular variance. Our neighbour-joining tree showed early and late runs generally clustering separately, indicating higher gene flow among the early or late run fish across years relative to between-run gene flow. Two years did not fit the general clustering pattern; although the early and late runs in 1995 and 2000 were genetically differentiated, they clustered separately from the rest of the groups. We cannot offer a definitive explanation for these anomalies; however, an analysis of possible cryptic population structure in early and late runs indicated that at least a few fish strayed between the runs in each year, and the highest rate of mixing was in 1995 and 2000. Our data indicate that the runs are at least partially reproductively isolated as a result of temporal and/or spatial isolating mechanisms. Such reproductive isolation has important implications for conservation and management of the Klukshu sockeye salmon, and make them an evolutionarily interesting group because of parallels with incipient speciation.     

Sample sizes for length and density estimation of 0+ fish when using point sampling by electrofishing

Standard lengths of cyprinids at several sites in the River Great Ouse, England, were compared between catches taken using a conventional 15 × 3 m micromesh seine (pore diameter 2 mm) and using point sampling by electrofishing (PSE). No statistically significant differences in sites were found in six out of 10 trials. In nine out of 10 trials, the difference between the mean lengths differed by <1 mm. No serial bias was found between PSE and seine netting for cyprinid fishes between 14 and 100 mm SL, although variation between size classes was high, owing to small sample sizes. The coefficient of variation in fish length with size tended to increase with the age of 0+ Rutilus rutilus . The relationship between sample size (n) and variance ( s² ) was explained by s ²=13·9 n ^−1·24. Sampling more than 30 fish resulted in little increase in precision. The relationship between the mean catch per site (̄) and the variance of the mean estimate was log s ²=1·6039 log ̄ +0·973. The number of samples required to estimate density within a given variance range was: n =9·33 ̄ ^1·6–2 CV_̄ ⁻². Given the high variance-mean ratio, great care should be taken when interpreting density data collected using PSE, and 50 point samples is the minimum required for density estimation.     

Age, sex ratio and timing of the catch of kelts and ascending Atlantic salmon in the subarctic River Teno

By 15 June, 82% of the catch of Atlantic salmon Salmo salar kelts had been taken from the middle part of River Teno, northern Scandinavia. The median date of capture was 4 June for males and 8 June for females. Salmon of 1–4 sea–winters (SW) of both sexes survived spawning to return to sea as kelts. Among males, 1 SW kelts were caught earliest in the spring and 3 SW latest, but among females 4 SW were earliest, then 3 SW and finally 1 and 2 SW. There were 17 river and sea–age combinations among the kelts compared with 23 among the ascending salmon. The smolt age distribution and the mean smolt age differed significantly only between female 2 SW ascending salmon (3·97 years) and kelts (4·14 years). The proportion of 1 SW females was higher and that of 3 SW males lower among kelts than among ascending salmon. The proportion of males among 1 SW ascending salmon was 80% but among kelts only 57%. Similarly, the proportion of males among 3 SW fish was 21% for ascending salmon but only 7% for kelts. Hence overwinter mortality was higher among males. Male and female kelts of 1 and female kelts of 2 SWhad a greater mean length than ascending salmon in corresponding groups indicating a better survival of larger fish within an age group. Grilse ascend rivers after most kelts have left, but the main catch of ascending 2–3 SW salmon takes place concurrently with kelts leaving the river, inadvertently targeting kelts in the fishery.     

Archival genetic analysis suggests recent immigration has altered a population of Chinook salmon in an unsupplemented wilderness area

Detecting genetic population shifts (i.e. allele frequency differences) through time is a primary function of effective conservation monitoring, but it is equally vital to understand the underlying causative factors of change which may be revealed through analyses of long-term, temporal trends. We compared archival and contemporary Chinook salmon (Oncorhynchus tshawytscha) collections from the John Day River in Oregon, USA, to evaluate the temporal relationships among four primary spawning areas over a span of 28 years (1978–2006). Although it lies amid many hatchery-supplemented salmon populations of the Columbia River, the John Day River has itself experienced no directed supplementation. Using a combined panel of 13 microsatellite and 92 single nucleotide polymorphism loci, we observed significant temporal heterogeneity across sample sites and tested for two likely evolutionary influences: stochastic processes (i.e. genetic drift) and gene flow via immigration. Based on abundance and effective population size estimates, we found no evidence indicating a recent bottleneck. We observed a sharp temporal decline in probability of self-assignment of John Day River fish, particularly for the North Fork tributary. There was a corresponding increase in assignment to distant Snake River populations, attributed to accumulating introgression from out-of-basin sources over time. Our study demonstrates that low level immigration sustained over multiple generations can alter the genetic composition of natural populations, and while immigration may help maintain genetic population diversity, it risks reducing adaptive advantages in local ecosystems.     

Population structure and impact of supportive breeding inferred from mitochondrial and microsatellite DNA analyses in land-locked Atlantic salmon Salmo salar L.

Four tributaries of Lake St-Jean (Québec, Canada) are used for spawning and juvenile habitat by land-locked Atlantic salmon. Spawning runs have drastically declined since the mid-1980s, and consequently, a supportive-breeding programme was undertaken in 1990. In this study, we analysed seven microsatellite loci and mtDNA, and empirically estimated effective population sizes to test the hypotheses that (i) fish spawning in different tributaries form genetically distinct populations and (ii) the supportive breeding programme causes genetic perturbations on wild populations. Allele frequency distribution, molecular variance and genetic distance estimates all supported the hypothesis of genetic differentiation among salmon from different tributaries. Gene flow among some populations was much more restricted than previously reported for anadromous populations despite the small geographical scale (40 km) involved. Both mtDNA and microsatellites revealed a more pronounced differentiation between populations from two tributaries of a single river compared with their differentiation with a population from a neighbouring river. The comparison of wild and F₁-hatchery fish (produced from breeders originating from the same river) indicated significant changes in allele frequencies and losses of low-frequency alleles but no reduction in heterozygosity. Estimates of variance and inbreeding population size indicated that susceptibility to genetic drift and inbreeding in one population increased by twofold after only one generation of supplementation.     

Assessment of genetic variation between reproductive ecotypes of Klamath River steelhead reveals differentiation associated with different run-timings

Seven microsatellite DNA loci were optimized to assess genetic differentiation in coastal steelhead (Oncorhynchus mykiss irideus) sampling groups from the lower Klamath River (California, USA). Genetic relationships among three winter‐run and two summer‐run groups were investigated. The different groups displayed high levels of allelic variation. Pairwise F_ST comparisons and Nei's genetic distance supported low, yet significant, genetic differentiation between summer and winter run‐timings similar to other studies of temporal variation in salmonids. Analysis of molecular variance showed that most of the genetic variation was at the individual level (97.9%), although significant genetic variation existed between timing of runs (2.59%). Additionally, at least one locus in each group was out of Hardy–Weinberg equilibrium due to a deficiency in heterozygotes, and significant F_IS values were observed in three temporal collections. Together, these results suggest stock admixture, caused by multiple populations of origin in each sampling group, better known as the Wahlund Effect. These observations are preliminary evidence for isolation by time between Klamath River steelhead runs during distinct periods.     

Genetic structure of juvenile cohorts of bicolor damselfish ( Stegastes partitus ) along the Mesoamerican barrier reef: chaos through time

Dispersal in marine systems is a critical component of the ecology, evolution, and conservation of such systems; however, estimating dispersal is logistically difficult, especially in coral reef fish. Juvenile bicolor damselfish (Stegastes partitus) were sampled at 13 sites along the Mesoamerican Barrier Reef System (MBRS), the barrier reefs on the east coast of Central America extending from the Yucatan, Mexico to Honduras, to evaluate genetic structure among recently settled cohorts. Using genotype data at eight microsatellite loci genetic structure was estimated at large and small spatial scales using exact tests for allele frequency differences and hierarchical analysis of molecular variance (AMOVA). Isolation-by-distance models of divergence were assessed at both spatial scales. Results showed genetic homogeneity of recently settled S. partitus at large geographic scales with subtle, but significant, genetic structure at smaller geographic scales. Genetic temporal stability was tested for using archived juvenile S. partitus collected earlier in the same year (nine sites), and in the previous year (six sites). The temporal analyses indicated that allele frequency differences among sites were not generally conserved over time, nor were pairwise genetic distances correlated through time, indicative of temporal instability. These results indicate that S. partitus larvae undergo high levels of dispersal along the MBRS, and that the structure detected at smaller spatial scales is likely driven by stochastic effects on dispersal coupled with microgeographic effects. Temporal variation in juvenile cohort genetic signature may be a fundamental characteristic of connectivity patterns in coral reef fishes, with various species and populations differing only in the magnitude of that instability. Such a scenario provides a basis for the reconciliation of conflicting views regarding levels of genetic structuring in S. partitus and possibly other coral reef fish species.     

Black liquor and the hangover effect: fish assemblage recovery dynamics following a pulse disturbance

Anthropogenic perturbations impact aquatic systems causing wide‐ranging responses, from assemblage restructuring to assemblage recovery. Previous studies indicate the duration and intensity of disturbances play a role in the dynamics of assemblage recovery. In August 2011, the Pearl River, United States, was subjected to a weak black liquor spill from a paper mill which resulted in substantial loss of fish in a large stretch of the main channel. We quantified resilience and recovery of fish assemblage structure in the impacted area following the event. We compared downstream (impacted) assemblages to upstream (unimpacted) assemblages to determine initial impacts on structure. Additionally, we incorporated historic fish collections (1988–2011) to examine impacts on assemblage structure across broad temporal scales. Based on NMDS, upstream and downstream sites generally showed similar assemblage structure across sample periods with the exception of the 2 months postdischarge, where upstream and downstream sites visually differed. Multivariate analysis of variance (PERMANOVA) indicated significant seasonal variation among samples, but found no significant interaction between impacted and unimpacted assemblages following the discharge event. However, multivariate dispersion (MVDISP) showed greater variance among assemblage structure following the discharge event. These results suggest that 2 months following the disturbance represent a time period of stochasticity in regard to assemblage structure dynamics, and this was followed by rapid recovery. We term this dynamic the “hangover effect” as it represents the time frame from the cessation of the perturbation to the assemblage's return to predisturbance conditions. The availability and proximity of tributaries and upstream refugia, which were not affected by the disturbance, as well as the rapid recovery of abiotic parameters likely played a substantial role in assemblage recovery. This study not only demonstrates rapid recovery in an aquatic system, but further demonstrates the value of continuous, long‐term, data collections which enhance our understanding of assemblage dynamics.     

A method for tracking the behaviour of mature and immature salmon parr around nests during spawning

A remote monitoring system was developed to provide information on the behaviour of mature and immature Atlantic salmon Salmo salar parr at nests during the spawning season. An octagonal passive integrated transponder (PIT) detector (0·865 m maximum diameter) designed to surround nests of Atlantic salmon was used to identify individual salmon parr present at 38 spawning events in three circular spawning channels. The range of the detector for PIT tags presented in the optimum orientation was 2·4 cm (range between tags 1·7–3·0 cm). Using a sub-sample of 20 spawnings, the mean efficiency of the detector (number of fish passes registered relative to number of passes observed on video) was 70·5% (range 32-100%). There were no significant effects of time from spawning, total number of registrations, body size or maturity status (mature or immature) on efficiency. However, fish were more likely to be detected entering nests than leaving, as departures were more rapid and higher in the water column. The PIT detector did not affect the numbers of parr at spawnings or between spawning intervals of females, and allowed for the individual identification of 65 of the 72 parr observed in nests during spawning. In all cases where certain identifications were not possible and the video was of satisfactory quality, this was due to obstruction of the camera view by anadromous fish. The remote monitoring system was thus effective in identifying behavioural differences, and only one of 20 immature parr was ever detected during the period encompassing 10 min before and after spawning compared with 30 or 40 mature parr.     

Latitudinal variability in lunar spawning rhythms: absence of a lunar pattern in the northern mummichog Fundulus heteroclitus macrolepidotus

In this study, the natural spawning season of the northern mummichog Fundulus heteroclitus macrolepidotus was examined from May to July in the lower St John River, New Brunswick, Canada (45° N), through measurements of gonado-somatic index ( I _G), liver-somatic index ( I _L) and condition factor ( K ). I _G increased during the prespawning phase (mean ± s.e. 5·49 ± 0·20%), peaked during the spawning phase (14·68 ± 0·51%) and dropped during the regression phase (3·23 ± 0·29%). A single peak of spawning was observed in F. h. macrolepidotus , contrasting with multiple peaks observed in studies south of 41° N in North America. Within the prespawning phase, there were significant differences between sampling dates in female body mass, gonad mass, liver mass and K . On the basis of results from this study, water temperature is believed to be the predominant factor controlling initiation of spawning in F. h. macrolepidotus .     

Genetic monitoring of wild and repatriated populations of endangered razorback sucker (Xyrauchen texanus, Catostomidae, Teleostei) in Lake Mohave, Arizona-Nevada

The Native Fishes Work Group, formed in 1991, developed and implemented a protocol to enhance the dwindling razorback sucker population in Lake Mohave, Arizona-Nevada. This large, genetically diverse population is severely reduced in size as a result of recruitment failure associated with predation on larvae. To circumvent this problem, wild larvae are captured, reared in protective custody until they are large enough to escape predation, and then released back into the lake. We present results of a monitoring program designed to assess the effectiveness of the sampling design in transmitting the high genetic diversity found in wild adults. Variation in a fragment from the mitochondrial DNA gene cytochrome b was examined by analysis of single-stranded polymorphisms and direct sequencing. Samples were characterized from three life history stages. Characterization of wild adults verified previous results that identified considerable diversity and provided baseline data. Samples of larvae from several temporal collections from throughout the spawning season and four geographical areas were characterized for 7 years (1997-2003) to assess the transmission of genetic variation from wild adults to larvae. Several analyses identified significant differences among temporal collections, resulting from sampling errors associated with finite number of females spawning at a given time and place. Comparisons among areas and years failed to identify significant variation, indicating that pooled collections for each year possess the same levels and patterns of genetic variation. Examination of repatriates representing 11 years (1992-2002) also failed to identify significant differences among cohorts; however, some sample sizes were small and the amova may lack sufficient power to detect differences. Contrasts of wild adults, larvae, and repatriates identified statistically significant differences among collections within these three groups; however, levels of variation are small and not biologically meaningful. More importantly, this analysis failed to detect significant differences among adults, larvae, and repatriates indicating that the program has been achieving its goal of transmitting variation from adults through the larvae and into the repatriate population. The reproductive capability of repatriates has not been examined, so it is unknown if the program will maintain genetic variation found in the original adult population. This will be most easily achieved by periodic monitoring of genetic variation in larval samples. If levels of variation become reduced in repatriates, levels and patterns of diversity in larvae are also expected to become reduced, and deviations in estimates of genetic diversity may become larger and more frequent. If this is the case, intervention may be necessary to ensure that certain individuals are not over-represented in the repatriate population.     

Temporal variation in habitat use by nekton in a subtropical estuarine system

Utilisation by fish of different estuarine habitats is known to vary at many different temporal scales, however no study to date has examined how utilisation varies at all the relevant times scales simultaneously. Here, we compare the utilisation by fish of sandy, intertidal foreshore habitats in a subtropical estuary at four temporal scales: between major spawning periods (spring/summer and winter), among months within spawning periods, between the full and new moon each month, and between night and day within those lunar phases. Comparisons of assemblage composition, abundance of individuals and of fish in seven different ‘ecological guilds’ were used to identify the temporal scales at which fish varied their use of unvegetated sandy habitats in the lower Noosa Estuary, Queensland, Australia. Fish assemblages were sampled with a seine net at three different regions. The most numerically dominant species caught were southern herring (Herklotsichthys castelnaui: Clupeidae), sand whiting (Sillago ciliata: Sillaginidae), weeping toadfish (Torquigener pleurogramma: Tetraodontidae), and silver biddy (Gerres subfasciatus: Gerreidae). Considerable variation at a range of temporal scales from short term (day versus night) to longer term (spawning periods) was detected for all but one of the variables examined. The clearest patterns were observed for diurnal effects, where generally abundance was greater at night than during the day. There were also strong lunar effects, although there were no consistent patterns between full moon and new moon periods. Significant differences among months within spawning periods were more common than differences between the actual spawning periods. The results clearly indicate that utilisation of sandy, unvegetated estuarine habitats is very dynamic and highly variable in space and time.     

Discriminating coho salmon (Oncorhynchus kisutch) populations within the Fraser River, British Columbia, using microsatellite DNA markers

Three microsatellite loci were used to examine genetic variation among 16 coho salmon ( Oncorhynchus kisutch ) populations within the Fraser River drainage system, in British Columbia, Canada. Each locus was highly polymorphic with 30 alleles at the Ots 101 locus, 15 alleles at the Ots 3 locus and 38 alleles at the Ots 103 locus. Average observed heterozygosities were 86.1%, 70%, and 56.1%, respectively. With the exception of the Dunn and Lemieux River populations, Chi-square tests and F _ST values indicated that all populations had significantly different allele frequencies. Two distinct population groups within the Fraser River drainage were observed. Lower Fraser River populations were strongly differentiated from populations spawning in the upper Fraser River, which includes the Thompson River (a tributary flowing into the upper Fraser) and the portion of the Fraser River beyond the precipitous Fraser River canyon. This regional population structure may have resulted from colonization of the upper and lower Fraser River regions by different founder populations following Pleistocene glaciation, and be maintained by adaptive differences between the two groups of coho salmon. Coho salmon populations in the upper Fraser and Thompson River drainages form an evolutionarily significant unit (ESU) of importance for conservation of biodiversity in coho salmon. Microsatellite DNA loci show promise as technically simple and highly informative genetic markers for coho salmon population management.     

Energetics and morphology of sockeye salmon: effects of upriver migratory distance and elevation

Depending on population, wild Fraser River sockeye salmon Oncorhynchus nerka travel distances of <100 km to >1100 km and ascend elevations ranging from near sea‐level to 1200 m to reach spawning areas. Populations embarking on distant, high elevation migrations ( i.e . Early Stuart, Chilko and Horsefly populations) began their upriver spawning migrations with higher densities of somatic energy ( c . 9·2 to 9·8 MJ kg⁻¹) and fewer eggs ( c . 3200 to 3800) than populations making shorter, low elevation migrations ( i.e . Weaver and Adams; c . 7·1 to 8·3 MJ kg⁻¹ gross somatic energy and c . 4300 to 4700 eggs). Populations making difficult upriver migrations also had morphologies that were smaller and more fusiform than populations making less difficult migrations, traits that may facilitate somatic energy conservation by reducing transport costs. Indeed, fish travelling long distances expended less somatic energy per unit of migratory difficulty than those travelling shorter distances (2·8 to 3·8 kJ v . 10–1400 kJ). Consistent with evolutionary theory, difficult migrations appear to select for energy efficiency but ultimately fish making more difficult migrations produce fewer eggs, even when differences in body length have been accounted for. Despite large among‐population differences in somatic energy at the start of upriver migration, all populations completed migration and spawning, and subsequently died, with c . 4 MJ kg⁻¹ of energy remaining, a level which may reflect a threshold to sustain life.     

Morphometric recognition of two morphs in sterlet (Acipenser ruthenus) population induced by different reproductive behaviour

Four species of sturgeons appear in the Yugoslav part of the Danube River. Among them three are anadromous, beluga ( Huso huso ), Russian sturgeon ( Acipenser gueldenstaedtii ) and stellate sturgeon ( Acipenser stellatus ) and migrate to Danube from the Black Sea to spawn. Only sterlet ( Acipenser ruthenus ) is exclusively freshwater. There are obvious differences between vernal and winter races of anadromous sturgeons, due to their different migratory patterns. Russian ichthyologist Berg (1934) claimed that there are two races (morphs) in the starlet population as well. This stimulated long discussion in Russian and Yugoslav literature, and it was the starting point for our research on sterlet in the Yugoslav part of the Danube River.
Morphometric analysis was preformed on 159 individuals caught in Danube River among 1123 and 1173 km, on four localities during September and October 2002. Analysis included 24 morphological and 3 meristic characters. K‐means cluster analysis indicated existence of two different clusters (groups), one with 95 (59·75%) and other with 64 (40·25%) samples. Significant differences were found for preorbital, preoral and prebarbel length. Mean values (in % of head length) for first group were 50·13 ± 1·71, 57·61 ± 1·87, 39·74 ± 2·20 and for second group 53·50 ± 2·46, 62·07 ± 2·20 and 43·30 ± 2·08 respectively. Findings were confirmed by Principal Components & Classification Analysis. These results speak in favour of existence of two morphs in sterlet population, one with long and pointed rostrum (vernal) and other with short rostrum (winter). According to the literature that is probably influenced by different reproductive behaviour (time separation in spawning).     

Reproductive biology of the threatened golden galaxias Galaxias auratus Johnston and the influence of lake hydrology

Golden galaxias Galaxias auratus (31–235 mm fork length, L _F) were collected monthly from littoral habitats in Lakes Crescent and Sorell, Tasmania, Australia, between July 2000 and December 2002. Spawning habitats were identified and monitored in both lakes, and surveyed in Lake Crescent. Trends in gonado-somatic indices and reproductive stages of development indicated that gonad development in both sexes begins in midsummer and peaks in late autumn to early winter. Males mature at smaller sizes (50% at 52 mm L _F) than females (50% at 76 mm L _F), larger individuals are predominately females (95% of fish ≥138 mm L _F), and overall male to female ratios are female biased ( c . 1:2). Spawning occurs late autumn to early spring (water temperatures = 1·4–9·7° C) with peaks in spawning activity in winter (mean water temperatures <5° C). Demersal adhesive eggs ( c. 1·5 mm diameter) were found on cobble substrata ( c. 20–250 mm diameter) in littoral areas ( c. 0·2–0·6 m deep) and fecundity of fish 71–181 mm L _F ranged from 619 to 14 478 eggs. The rate of change in water level over the 20 days prior to monthly sampling was important in explaining the occurrence of spent fish and this accounted for temporal differences in spawning between the populations. Lake hydrology influences the reproductive cycle of G. auratus by possibly providing a stimulus for spawning and it controls the availability of spawning habitat in Lake Crescent. Seasonal hydrological cycles ( i.e. rises during late autumn to winter) and a minimum water level of 802·20 m Australian Height Datum in Lake Crescent during autumn (above which littoral areas of cobble substratum are inundated) are critical to G. auratus populations.     

Microsatellites reveal high levels of gene flow among populations of the California squid Loligo opalescens

Information on the extent of genetic differentiation among populations of the squid Loligo opalescens is crucial for the conservation of this commercially utilized species. We analysed six highly variable microsatellite loci in 11 collections of L. opalescens from different locations and spawning seasons to estimate the relative influence of two major evolutionary forces, gene flow and genetic drift. Microsatellite allele frequency patterns suggest that gene flow prevents population differentiation in L. opalescens. Tests for genetic differentiation showed homogeneity of the samples with an overall FST/RST of 0.0028/-0.0013. Genetic uniformity among samples from different year classes indicates that allele frequency patterns in L. opalescens are relatively stable over time. However, a more complete and detailed picture of fine-scale allele frequency shifts in this species will require a systematic microsatellite analysis of local populations over consecutive spawning cycles.