Reproduction,growth and feeding habits of stout beardfish Polymixia nobilis (Polymixiidae) off the Canary Islands (NE Atlantic)

The present study provides fisheries biology knowledge which will allow the implementation of regulatory measures contributing to the sustainability of the fisheries and the conservation of the stout beardfish Polymixia nobilis Lowe, 1838 off the Canary Islands, north eastern Atlantic Ocean. Males ranged between 16.5 and 38.4 cm fork length (FL) and females from 14.2 to 46.5 cm FL. Sex ratio by size classes provided significant differences in classes higher than 36 cm, being clearly unbalanced in favour of females. Individuals in maturing and mature stages were present during all months sampled, although a spawning peak is evident between April and June. Size at first maturity was estimated as 26 cm FL for females and 30 cm FL for males. Age was determined from annuli in whole otoliths. Age range was found to be 0–14 years for fish measuring 14.2 to 46.5 cm FL. It is a slow‐growing and long‐lived species. Significant differences in the growth parameters between sexes were detected. The von Bertalanffy growth parameters estimated for females (n = 213) were L_∞ = 45.92 cm LF, k = 0.16 years^?1 and t₀ = ?2.84 years; and for males (n = 186) L_∞ = 36.44 cm LF, k = 0.26 years^?1 and t₀ = ?2.16 years. Stomach analysis indicated some variations in the feeding habits with growth: individuals of small and medium sizes preyed on crustaceans and fishes, while large specimens preyed mainly on fishes.     

Effect of wave exposure dynamics on gut content mass and growth of young‐of‐the‐year fishes in the littoral zone of lakes

Total length, body mass and gut content mass of young‐of‐the‐year (YOY) perch Perca fluviatilis, dace Leuciscus leuciscus and bleak Alburnus alburnus were recorded over the summer of 2006 at three littoral sites at Upper Lake Constance. In P. fluviatilis and L. leuciscus, gut content mass correlated positively with wave‐induced energy flux (E_F) of the respective site and sampling day, while no correlation of gut content mass with E_F was found in A. alburnus. It was assumed that benthivorous P. fluviatilis and L. leuciscus profited from suspended or uncovered benthic food items generated by wave action at sites and periods with high E_F. Alburnus alburnus, in contrast, feeding mainly on zooplankton in upper parts of the water column, could not profit from increased E_F. In P. fluviatilis, increased gut content mass during periods of high E_F resulted in higher growth rates. For L. leuciscus, no real growth rates in local fish populations could be determined, as individuals were less sedentary, and when increased growth occurred at sites during the periods of high E_F, migration of fish levelled out the resulting size differences within few days. The results of this study show that dynamic habitat variables affect site profitability in the littoral zone of lakes, especially in benthivorous fishes. Therefore, dynamic habitat variables should be considered in addition to fixed habitat properties in analyses of habitat choice of fishes in the littoral zone of lakes.     

Reproductive traits of the dwarf gobies Pandaka trimaculata and Pandaka lidwilli in the western Pacific Ocean: histological evidence from one of the smallest fishes in the world

Gobies are generally small fishes which play important roles in estuarine ecosystems, yet little attention has been paid to their life-history traits in the western Pacific region. In the present study, the reproductive traits of the dwarf gobies Pandaka trimaculata and Pandaka lidwilli were explored by examining their populations in a subtropical estuary on Okinawa-jima Island, Japan, over 15 months. The Okinawan populations of both species shared similar reproductive traits. Pandaka trimaculata and P. lidwilli exhibited early female maturation at minimum sizes of 8.8 and 9.4 mm standard length (SL), respectively, which indicate that populations of the Pandaka species in the subtropical region represent some of the smallest fishes in the world. Nonetheless, they also had high relative body sizes at maturity relative to the attained asymptotic SLs, ranging from 75.8% to 80.4%, which suggests that their populations are vulnerable to negative impacts. Both the species also had prolonged spawning periods, extending from February to November (P. trimaculata) and from January to October (P. lidwilli), indicating that these local populations have a high potential for maintenance and resilience. Their spawning periods, sizes at maturity and fecundities varied among seasons and latitudes, possibly because of low water temperatures affecting the relative allocation of energy to growth and reproduction. Such plasticity of life-history traits in these small fishes indicates that they would be suitable models for understanding the evolution of life-history strategies and monitoring the responses of organisms to climate change.     

Age and growth of grey triggerfish Balistes capriscus from trans-Atlantic populations

Anthropogenic factors that negatively impact reef fishes can include changes in life-history patterns of fisheries-targeted species. Understanding these impacts on growth and population age structure is essential in the management of exploited populations of fishes. This is the first study to directly compare age and growth for a major fisheries species between east and west populations of a transatlantic reef fish. The main goal of this study was to document age and growth in grey triggerfish Balistes capriscus from coastal waters of Ghana in the Gulf of Guinea (GOG) and compare those with the previous growth studies from that region and with the western Atlantic population. A secondary objective of this study was to evaluate the use of otoliths to age triggerfish and to provide a preliminary comparison with spine-derived age estimates. The results obtained from this study provided an updated understanding of the growth and age structure of the eastern B. capriscus population in GOG. The authors documented that shifts in population attributes occurred for B. capriscus after its major decline in abundance. The differences in physical and biotic characteristics of the East and West Atlantic regions and the differences in collection methods of samples make direct comparisons of growth parameters difficult. Nonetheless, overall differences in maximum sizes and ages were apparent; the western Atlantic population had a larger maximum size and older maximum age. The authors also documented that sagittal otoliths can be used to provide age estimates for triggerfish species, and otoliths as an ageing structure had better between-reader precision compared to dorsal spines.     

HYBRID ZONE DYNAMICS ARE INFLUENCED BY GENOTYPE-SPECIFIC VARIATION IN LIFE-HISTORY TRAITS: EXPERIMENTAL EVIDENCE FROM HYBRIDIZING GAMBUSIA SPECIES

Results from two experiments are presented that contrast differences in life-history traits and population dynamics between two species of live bearing fishes (Gambusia affinis and G. holbrooki) that hybridize across portions of the southeastern United States. Progeny from parental holbrooki and holbrooki-affinis F₁ crosses exhibited larger lengths at birth, at 15 days, and matured earlier, and at larger size than did progeny from parental affinis and affinis-holbrooki F₁ crosses. Comparisons of experimental populations of affinis, holbrooki, and mixed (affinis + holbrooki) species composition followed over two years revealed that affinis populations consistently exhibited smaller population size, lower carrying capacity, lower recruitment, and larger over-winter mortality than did holbrooki or mixed populations. Evidence for density-dependent reductions in fecundity and concomitant increases in juvenile mortality rates were observed in all populations, but were most pronounced for affinis populations. Genotype-specific differences in life-history traits appear to confer differential advantage to offspring of parental holbrooki origin and F, progeny of holbrooki maternal parentage given the resource availability and the age structure and densities experienced during these experiments. Results have direct implications regarding the rate and direction of evolution within hybrid zones formed by these two species.     

Intraspecific variability in the life histories of endemic coral-reef fishes between photic and mesophotic depths across the Central Pacific Ocean

Mesophotic coral ecosystems (MCEs) represent the lowest depth distribution inhabited by many coral reef-associated organisms. Research on fishes associated with MCEs is sparse, leading to a critical lack of knowledge of how reef fish found at mesophotic depths may vary from their shallow reef conspecifics. We investigated intraspecific variability in body condition and growth of three Hawaiian endemics collected from shallow, photic reefs (5–33 m deep) and MCEs (40–75 m) throughout the Hawaiian Archipelago and Johnston Atoll: the detritivorous goldring surgeonfish, Ctenochaetus strigosus, and the planktivorous threespot chromis, Chromis verater, and Hawaiian dascyllus, Dascyllus albisella. Estimates of body condition and size-at-age varied between shallow and mesophotic depths; however, these demographic differences were outweighed by the magnitude of variability found across the latitudinal gradient of locations sampled within the Central Pacific. Body condition and maximum body size were lowest in samples collected from shallow and mesophotic Johnston Atoll sites, with no difference occurring between depths. Samples from the Northwestern Hawaiian Islands tended to have the highest body condition and reached the largest body sizes, with differences between shallow and mesophotic sites highly variable among species. The findings of this study support newly emerging research demonstrating intraspecific variability in the life history of coral-reef fish species whose distributions span shallow and mesophotic reefs. This suggests not only that the conservation and fisheries management should take into consideration differences in the life histories of reef-fish populations across spatial scales, but also that information derived from studies of shallow fishes be applied with caution to conspecific populations in mesophotic coral environments.

     

Genetic clustering methods reveal bull trout (<Emphasis Type="Italic">Salvelinus confluentus</Emphasis>) fine-scale population structure as a spatially nested hierarchy

Many conservation genetics studies in fishes define populations based on capture location. In salmonid fishes, this traditional a priori designation is made by spawning stream, with subsequent post hoc approaches used to define units of conservation. In this study of bull trout from southwestern Alberta, we provide evidence that a model-based Bayesian genetic clustering method may provide a more parsimonious alternative to designating population structure and units of conservation in comparison to traditional methods. The clustering method captured a hierarchical model of population structure, in which seven local populations were nested within three genetic archipelagos. This was in contrast to using simple F _ST based approaches between thirteen a priori designated populations, which found significant differences for nearly every pairwise comparison. In addition, assignment tests results from Bayesian clustering revealed that movement may be common between sampling locations. These clustering methods are easy to use, intuitive and provide substantial information on populations of fish; this study provides an example of their utility for local fisheries management and conservation.     

The potential use of scales for estimating age and growth of Mediterranean albacore (Thunnus alalunga)

The ability to accurately estimate the age of fishes is critical for conducting stock assessments and developing fishery management policies. Scales were collected from albacore, Thunnus alalunga, caught in the Mediterranean Sea during the years 1989–1995 to estimate their age and growth. Ages, which ranged from 1+ to 6+ years, were estimated from the interpretation of the concentric rings on the scales of 473 individuals that ranged in fork length from 55.5 to 89 cm. Males reached a greater size and age than females. The relatively close agreement in the mean lengths at ages estimated by scales and other techniques constituted a preliminary verification of the method. The von Bertalanffy growth model was fitted to mean lengths at estimated ages, resulting in the following growth parameters for the combined sexes: L_∞ = 86 cm, K = 0.4, t_o = ?0.8 years. Parameter estimates were in agreement with what is known about life history of the species in the Mediterranean. Moreover, the growth rates were consistent with length increment observations from five tag returns, which lend support to our working hypothesis that the scale‐rings are annual structures. When the Mediterranean albacore growth parameters were compared with those of Atlantic Ocean albacore using scale age estimates, there were significant differences between the two populations, and Mediterranean albacore remain significantly smaller than Atlantic Ocean albacore.     

An integrative taxonomic review of the Natal mountain catfish,Amphilius natalensis Boulenger 1917 (Siluriformes,Amphiliidae), with description of four new species

Species delimitation is a permanent issue in systematics. The increasing recognition of geographically isolated populations as independent lineages allowed by new methods of analysis has inflated the species-populations dilemma, which involves deciding whether to consider separate lineages as different species or structured genetic populations. This is commonly observed between fishes of adjacent river basins, with some lineages being considered allopatric sister species and others considered isolated populations or variants of the same species. Pseudocorynopoma doriae is a characid diagnosed from its single congener by the number of anal-fin rays and sexually dimorphic characters of males, including distinct fin colouration. The authors found variation in the colour pattern between isolated populations previously identified as P. doriae but no variation in scale or fin-ray counts. They analysed molecular evidence at the population level and morphological differences related to life history (e.g., colour dimorphism related to inseminating behaviour). The results provide compelling evidence for the recognition of a new species of Pseudocorynopoma despite the lack of discrete differences in meristic data. The recognition of the new species is consistent with biogeographical evidence for the long-term isolation of the respective river drainages and with differences between the ichthyofaunal communities of these rivers.     

The impact of elevated CO2 on growth and photosynthesis in Agrostis canina L. ssp. monteluccii adapted to contrasting atmospheric CO2 concentrations

 The aim of this study was to characterise growth and photosynthetic capacity in plants adapted to long-term contrasting atmospheric CO₂ concentrations (C _a). Seeds of Agrostis canina L. ssp. monteluccii were collected from a natural CO₂ transect in central-western Italy and plants grown in controlled environment chambers at both ambient and elevated CO₂ (350 and 700 μmol mol⁻¹) in nutrient-rich soil. Seasonal mean C _a at the source of the plant material ranged from 610 to 451 μmol CO₂ mol⁻¹, derived from C₄ leaf stable carbon isotope discrimination (δ¹³C). Under chamber conditions, CO₂ enrichment stimulated the growth of all populations. However, plants originating from elevated C _a exhibited higher initial relative growth rates (RGRs) irrespective of chamber CO₂ concentrations and a positive relationship was found between RGR and C _a at the seed source. Seed weight was positively correlated with C _a, but differences in seed weight were found to explain no more than 34% of the variation in RGRs at elevated CO₂. Longer-term experiments (over 98 days) on two populations originating from the extremes of the transect (451 and 610 μmol CO₂ mol⁻¹) indicated that differences in growth between populations were maintained when plants were grown at both 350 and 700 μmol CO₂ mol⁻¹. Analysis of leaf material revealed an increase in the cell wall fraction (CWF) in plants grown at elevated CO₂, with plants originating from high C _a exhibiting constitutively lower levels but a variable response in terms of the degree of lignification. In vivo gas exchange measurements revealed no significant differences in light and CO₂ saturated rates of photosynthesis and carboxylation efficiency between populations or with CO₂ treatment. Moreover, SDS-PAGE/ LISA quantification of leaf ribulose bisphosphate carboxylase/oxygenase (Rubisco) showed no difference in Rubisco content between populations or CO₂ treatments. These findings suggest that long-term adaptation to growth at elevated CO₂ may be associated with a potential for increased growth, but this does not appear to be linked with differences in the intrinsic capacity for photosynthesis. Received: 16 August 1996 / Accepted: 19 October 1996     

Nutrient recycling by two phosphorus-rich grazing catfish: the potential for phosphorus-limitation of fish growth

In ecosystems where excretion by fish is a major flux of nutrients, the nitrogen (N) to phosphorus (P) ratio released by fish can be important in shaping patterns of algal biomass, community composition, primary production, and nutrient limitation. Demand for N and P as well as energy influences N/P excretion ratios and has broad implications in ecosystems where nutrient recycling by fishes is substantial. Bioenergetics and stoichiometric models predict that natural fish populations are generally energy-limited and therefore N/P recycling by fishes is relatively invariant. Yet, the potential for P limitation of growth has not been examined in herbivorous fishes, which are common in many aquatic habitats. We examined N/P excretion ratios and P demand in two P-rich herbivorous catfishes of the family Loricariidae, Ancistrus triradiatus (hereafter Ancistrus) and Chaetostoma milesi (hereafter Chaetostoma). Both fishes are common grazers in the Andean piedmont region of Venezuela where we conducted this study. Mass balance (MB) models indicate that these fishes have a high P demand. In fact, our Ancistrus’ P MB model predicted negative P excretion rates, indicating that Ancistrus did not consume enough P to meet its P demand for growth. Direct measurement of excretion rates showed positive, but very low P excretion rates and high N/P excretion ratios for both taxa. To obtain measured P excretion rates of Ancistrus from the MB model, gross growth efficiency must be reduced by 90%. Our results suggest that growth rates of both of these herbivorous and P-rich fish are likely P-limited. If P limitation of growth is common among herbivorous fish populations, herbivorous fishes recycle likely at high N/P ratios and act to diminish the quality of their food.     

Phylogeography,more than elevation,accounts for sex chromosome differentiation in Swiss populations of the common frog (Rana temporaria)*

Sex chromosomes in vertebrates range from highly heteromorphic (as in most birds and mammals) to strictly homomorphic (as in many fishes, amphibians, and nonavian reptiles). Reasons for these contrasted evolutionary trajectories remain unclear, but species such as common frogs with polymorphism in the extent of sex chromosome differentiation may potentially deliver important clues. By investigating 92 common frog populations from a wide range of elevations throughout Switzerland, we show that sex chromosome differentiation strongly correlates with alleles at the candidate sex-determining gene Dmrt1. Y-specific Dmrt1 haplotypes cluster into two main haplogroups, Y_A and Y_B, with a phylogeographic signal that parallels mtDNA haplotypes: Y_A populations, with mostly well-differentiated sex chromosomes, occur primarily south of the main alpine ridge that bisects Switzerland, whereas Y_B populations, with mostly undifferentiated (proto-)sex chromosomes, occur north of this ridge. Elevation has only a marginal effect, opposing previous suggestions of a major role for climate on sex chromosome differentiation. The Y-haplotype effect might result from differences in the penetrance of alleles at the sex-determining locus (such that sex reversal and ensuing X-Y recombination are more frequent in Y_B populations), and/or fixation of an inversion on Y_A (as supported by the empirical observation that Y_A haplotypes might not recombine in XY_A females).     

Identification and analysis of a novel microsatellite marker within the growth hormone gene promoter of Colossoma macropomum (Characiformes: Characidae) detected by TAIL-PCR

While in all vertebrates, growth hormone (GH) promotes post-natal growth, in fishes it also affects such metabolic functions as foraging rate, digestion, osmoregulation, and reproduction. The promoter region of the GH gene is an important target for studies of mechanisms regulating its expression, and polymorphisms within the promoter have been associated with performance traits in fishes. We used Thermal Asymmetric Interlaced PCR (TAIL-PCR) to amplify and sequence the 5′-flanking regions of the Colossoma macropomum GH (cmGH) gene. Based on a sequence of 1,038 bp, we designed three specific nested primers (R-290, R-186 and R-26) which were used with shorter arbitrary degenerate primers to amplify the 5′ proximal region of the cmGH gene. We identified a tetranucleotide (ATCC)₄ microsatellite motif in this region, exhibiting four alleles (118, 122, 126 and 130 bp) within the population study. Genotypes at this locus deviated significantly from Hardy–Weinberg expectations (p ≤ .05) and showed a low level of polymorphism (polymorphic information content = 0.163). High homozygosity (F_IS = 0.147) was observed in the overall population. The polymorphism at the microsatellite makes it an important candidate for association studies between the respective genotypes, growth rate and other traits in farmed populations. Such studies may contribute to future breeding programs using marker-assisted selection upon this aquaculturally important species.     

Growth pattern of the young of the year Argentine hake <Emphasis Type="Italic">Merluccius hubbsi</Emphasis> Marini, 1933 (Gadiformes Merluccidae) along the Brazilian and Uruguayan coasts

Morphology and morphometry of the sagittae otolith were studied in young of the year Argentine hake, Merluccius hubbsi in the Southeastern Atlantic. Geographical variation in the growth pattern of the young of the year Merluccius hubbsi was correlated with the differences found in otolith morphometry, relative growth, ring positions, as well as the formation of a new ring. The otolith development of M. hubbsi throughout its area of distribution accompanies an increasing northward temperature gradient, resulting in bigger otoliths and greater variability of ring position from northern to southern area. The canonical discriminate analysis showed that the otolith length and height explained most of the variation of the first discriminant function. We found significant differences in the discriminant scores between those samples from northern and southern area. As regards the Uruguayan coast and Southern Brazil, age groups zero shared some similarity as well as differences in growth; environmental features explain these differences but their effect on the adult fishes growth is still unknown.     

Age,growth and feeding habits of the bluemouth rockfish,Helicolenus dactylopterus dactylopterus (Delaroche 1809) in the central Mediterranean (southern Tyrrhenian Sea)

This paper provides data on age, growth and diet of the bluemouth rockfish, Helicolenus dactylopterus dactylopterus (Scorpaenidae), central Mediterranean Sea. Estimated by otolith readings, ages ranged from 0 to 21 years. Parameters of the von Bertalanffy growth curves were L_inf = 26.1 cm, k = 0.14 year^?1, t₀ = ?1.92 years and the growth performance index was Φ = 1.98. The weight‐length relationship, W = 0.016 TL^2.99; R² = 0.99, described an isometric growth of the species. This species is a carnivore focusing mainly on the crustaceans Goneplax rhomboides and Lophogaster typicus. Statistical analysis showed an ontogenetic shift between small (4.0–6.3 cm) and larger fishes. Significant differences were also found in relation to the sampling depth.     

The ultrastructure of the spermatheca in the red spotted newt

In continuing study of gene and genome interaction as a possible etiological mechanism in normal and abnormal growth and malformation, the ventral spinous processes (VSPs, crural insertions of the diaphragm) were used as additional epigenetic variants to portray differences in the basic gradient growth pattern. Over 700 comparisons of mean differences in number (range or magnitude) and peak (position) of the VSP gradient, in the same populations of strains III, DA, and III_Da (into which the Da gene had been introduced from strain DA), provided populations of +/+, Da/+ and Da/Da on two different genome backgrounds. They reveal the individual effects on the VSPs of underlying growth processes associated with the Da gene dosage, vertebral border shifts and stillbirths. Both Da and stillbirths demonstrate growth influences which interact additively to reduce the range and shift the peak anteriorly in opposition to those of the border shifts. The growth effects induced by border shifts are in some cases significantly so much greater as to seemingly inhibit or even reverse either the specific gene Da or stillbirth effects. The way that interaction of such growth influences can enhance, suppress or cancel each other and the relation to specific growth gradients and functions is of particular importance to understanding the etiology and growth mechanisms of spontaneous and unexpected exogenously or endogenously induced malformations in non-isogenic stocks.     

Genetic and morphoecological characteristics of peled <Emphasis Type="Italic">Coregonus peled</Emphasis> acclimatized in lakes of Tuva Republic

Morphoecological and genetic characters were studied of peled Coregonus peled naturalized in lakes of Tuva Republic. For comparison (as a donor), peled was considered from Leningrad oblast to originate from “wild” peled from Lake Endyr and dispersed widely into water bodies of the former Soviet Union. The results of analysis of variations in 18 polymorphic nuclear loci, coding the proteins (allozymes), and the part of mitochondrial (mt)DNA, coding the first subunit of NADH-dehydrogenase, attest genetic and morphoecological differentiation of populations formed in Tuva lakes. Significant differences were found between them in age composition, rate of growth, and external morphology. Statistically significant differences in allele frequencies of some loci were observed between the samples of acclimatized peled, though total level of genetic differentiation between the populations was not high (F _ST = 0.028). Estimates of gene diversity by allozyme loci were maximal in the population of alpine Lake Sut-Khol, but almost minimum diversity of mtDNA was observed in this population. It is obvious that “own” genetic appearance is formed in introduced fishes in every lake with peculiar diversity in the result of interaction between relatively homogeneous donor material and specific conditions of new environment, and this interaction is especially intense at the first stages of introduction.     

Indirect food web interactions increase growth of an algivorous stream fish

1. We tested the hypothesis that indirect food web interactions between some common, invertivorous fishes and their prey would positively affect growth of an algivorous fish species. Specifically, we predicted that orangethroat darter (Etheostoma spectabile) would increase periphyton biomass via a top‐down pathway, indirectly enhancing growth of the algivorous central stoneroller minnow (Campostoma anomalum). Moreover, we predicted that sand shiner (Notropis stramineus) would increase periphyton biomass via a bottom‐up pathway and indirectly enhance growth of the stoneroller minnow. 2. In an 83‐day experiment in large, outdoor, stream mesocosms, we stocked two fish species per mesocosm (stoneroller and either darter or shiner), estimated the effects of the invertivorous and grazing fishes on periphyton biomass and estimated growth of the algivorous fish. 3. The darter consumed grazing invertebrates, indirectly increasing periphyton biomass. The shiner consumed terrestrial insects as predicted, but it did not affect periphyton biomass. 4. In support of our hypothesis, the darter indirectly enhanced stoneroller growth. As predicted, stonerollers consumed the increased periphyton in streams with darters, resulting in greater growth, condition and gut fullness compared to streams without darters. No indirect interaction was observed between stonerollers and shiners. 5. Our study suggests that some invertivorous fish species can positively affect growth of algivorous fishes through indirect food web interactions. Thus, in stream communities, it is possible that the loss of a single, invertivorous fish taxon could have negative consequences on algivorous fish populations via the removal of positive indirect food web interactions.     

Dynamics of the Pikeperch,Stizostedion lucioperca (L.), in Lake Balaton

The pikeperch populations inhabiting three distinct water areas of Lake Balaton differ in regard of growth. Due to stock depletion, pikeperch in the NE-basin of the lake grew considerably faster than ten years ago. The annual rate of growth in length (von Bertalanffy's K) varied between 0.09 and 0.19. The specific rate of growth in length (G_L) ranged from 0.16 to 0.23 and that of growth in weight (G_W) from 0.52 to 0.69. Length and age-structures of the stocks differed significantly between different areas and years, but the overwhelming majority of the stocks consisted of age-groups IV–V (98.2–99.3%). From NE to SW, the rates of survival were 34, 29 and 70%, respectively. These differences, and the differences in growth resulted in changes in the productive capacity of the stocks. The ratios of production and biomass were 59% (NE-basin), 63% (central basin) and 39% (SW-basin), respectively. The magnitudes of production varied inversely. The 50% retention lengths of the seine nets used in Lake Balaton were 35.0, 35.7 and 42.5 cm with weights of 572, 655 and 1019 g, respectively.     

Genetic Diversity and the Reintroduction of Meadow Species

Abstract: Restoration of formerly nutrient‐poor and species‐rich grasslands generally leads to an increase in species diversity. However, species without a persistent seed bank and with poor dispersal ability often do not re‐establish spontaneously. Here, reintroduction is an option. If existing populations are comparable in their genetic composition, any population will do. This is not the case if populations have local adaptations. Unfortunately, whether populations are adapted locally is not easily determined, in contrast to assessing differentiation using neutral genetic markers. We used AFLP to study genetic diversity of Cirsium dissectum and Succisa pratensis within and among several Junco‐Molinion plant communities in the Netherlands (up to 200 km apart) that were potential source populations, and followed the reintroduction using seeds from these populations. Also, vegetative growth phase characteristics of three populations of C. dissectum were analyzed under controlled conditions. Most of the genetic variation in these cross‐fertilizing species was found within populations. Small but significant genetic differences in band frequencies were found among populations (F_st 0.100 ‐ 0.135). The first generation of reintroduced plants contained less polymorphic bands than the source populations. The genetic differences caused by reintroduction using a limited number of seeds (founder effects) were significant in all except one case (F_st 0.012 ‐ 0.101 between source and corresponding reintroduced population), but the magnitude was smaller than the source population differentiation. In assignment tests, reintroduced populations resembled their source population more than any other population, but all populations contained sizeable proportions of plants that were assigned to most similar plants from other populations, indicating that the populations are only marginally distinct. Calculations show that reintroduction from more than one source population introduces significantly more polymorphic bands into the new population, capitalizing on the existence of band frequency differences among populations.