The analysis of commercial fish population size oscillations in Lake Peipus

With the use of recurrence plots, we show that the irregular oscillations in time, which commercial fish populations in Lake Peipus undergo, are deterministic.     

Long-period endogenous oscillations in fish population size: Mathematical modeling

We present a mathematical model of an aquatic community, where the size-and-age structure of hydrobiont populations is taken into account and the corresponding trophic interactions between zooplankton, peaceful fish, and predatory fish are described. We show that interactions between separate components of the aquatic community can give rise to long-period oscillations in fish population size. The period of these oscillations is on the order of decades. With this model we also show that an increase in the zooplankton growth rate may entail a sequence of bifurcations in the fish population dynamics: steady states → regular oscillations → quasicycles → dynamic chaos.     

The rotifers of Lake Peipus

In the northern part of Lake Peipus, 140 taxa of rotifers were identified, with species of Anuraeopsis, Conochilus, Keratella, Polyarthra and Synchaeta dominating. Two main periods of sexual reproduction occur, in the spring and autumn. Different life cycle patterns are represented. Rotifer number and biomass have two maxima between spring and early autumn. The contribution of rotifers to total zooplankton production varies from 13.6% (Oct.) to 89.8% (May). The average production of grazing rotifers is 485.1 kJ m^–2, while that of predatory rotifers (Asplanchna) is 10.0 kJ m^–2.     

Population Dynamics of the Bream Abramis brama in Lake Peipus

Journal of Ichthyology - Population dynamics of the bream Abramis brama in lakes Peipsi and Pihkva for the period from 1980 to 2009 has been studied by means of cohort models. Bream stock increased...     

Genome size is negatively correlated with effective population size in ray-finned fish

A recent theory suggesting that genome size and complexity can increase as a passive consequence of small effective population size has generated much controversy. In this article, we demonstrate that freshwater fish species, which have smaller effective population sizes than marine fish species, have larger genomes. We show that genome size is negatively correlated with genetic variability, independent of phylogeny, body size and generation time. Genome duplication is also observed predominantly in freshwater fish. These results suggest that the raw materials of complexity originate under conditions of reduced selection efficiency.     

An age-structured fish population model with coupled size and population density

In this paper an age-structured fish population model in which fish size is included as a dynamic variable is formulated and analyzed. The main features of the model include size-dependent growth and mortality of young-of-the-year fish as well as size-related fecundity of adult females. The inclusion of cannibalism of young-of-the-year fish by yearlings, as it is represented in the model, can lead to some interesting stability behavior such as the existence of multiple equilibrium states. Depending on initial conditions, the population may evolve to either of two stable equilibrium states: one with relatively large numbers of small fish or one with relatively small numbers of large fish.     

The Seasonal Dynamics and Trophic Relations of the Plankton Components in Lake Peipsi (Peipus)

The seasonal dynamics of the biomass and production of phyto-, zoo- and bacterioplankton was investigated during the vegetation periods (from May to November) in 1985 and 1986 in the pelagial of the large eutrophic lake Peipsi (Estonia). The average values of productions per vegetation period for the investigation years were as follows: phytoplanktion − 203.5 gC · m⁻²; bacterioplankton − 37.9 gC · m⁻²; filter-feeding zooplankton − 20.6 gC · m⁻² and predatory zooplankton − 1.5 gC · m⁻². The herbivorous zooplankton production constituted 10.1% of primary production. This ratio indicates a direct relationship between zoo- and phytoplankton in the food chain — filtrators are feeding mostly on living algae and the detrital food chain seems of little importance. The dominance of large forms (Melosira sp., Aphanothece saxicola), in the phytoplankton during the major part of the vegetation period is assumed to be a result of high grazing pressure on small algae. Zooplankton grazing was investigated in situ in a specially constructed twin bathometer. Experimental measurements revealed, that zooplanktion presence in the experimental vessel actually stimulated the phytoplankton growth in many cases — the negative grazing values have been registered. That could be caused by the stimulation effect of nutrients (N, P), excreted by the concentrated zooplankton in the grazing chamber, which led to an increase of the nongrazed phytoplankton production. Bacteria have satisfied the zooplankton food requirements on average by 11%. Grazing on bacteria increased, when grazing on phytoplankton was somehow disturbed.     

Amplitude-encoded calcium oscillations in fish cells

The reaction of intracellular Ca(2+) to different agonist stimuli in primary hepatocytes from rainbow trout (Oncorhynchus mykiss) as well as the permanent fish cell line RTL-W1 was investigated systematically. In addition to "classical" agonists such as phenylephrine and ATP, model environmental toxicants like 4-nitrophenol and 3,4-dichloroaniline were used to elucidate possible interactions between toxic effects and Ca(2+) signaling. We report Ca(2+) oscillations in response to several stimuli in RTL-W1 cells and to a lesser extent in primary hepatocytes. Moreover, these Ca(2+) oscillations are amplitude-encoded in contrast to their mammalian counterpart. Bioinformatics and computational analysis were employed to identify key players of Ca(2+) signaling in fish and to determine likely causes for the experimentally observed differences between the Ca(2+) dynamics in fish cells compared to those in mammalian liver cells.     

Distinct population structure in a phenotypically homogeneous rock-dwelling cichlid fish from Lake Tanganyika

Several lineages of cichlid fishes in the East African Great Lakes display stunning levels of morphological diversification. The rapid evolution of rock-dwelling polygynous mouthbrooders in Lake Malawi, for example, was in part ascribed to their allopatric distribution on disjunct stretches of rocky coast, where even short habitat discontinuities reduce gene flow effectively. However, as seen in other cichlids, ecological barriers do not always prevent gene flow, whereas genetic structure can develop along continuous habitat, and morphological diversification does not necessarily accompany genetic differentiation. The present study investigates the population structure of Variabilichromis moorii, a monogamous substrate-brooding lamprologine of rocky coasts in Lake Tanganyika, which occurs over about 1000 km of shoreline almost without phenotypic variation. Phylogeographic analyses of mitochondrial DNA sequences indicated that dispersal is infrequent and generally occurs between adjacent locations only. Exceptions to this pattern are closely related haplotypes from certain locations on opposite lakeshores, a phenomenon which has been observed in other species and is thought to reflect lake crossing along an underwater ridge in times of low water level. Genetic population differentiation, estimated from mitochondrial DNA and microsatellite data in six adjacent populations, was equally high across localities separated by sandy shores and along uninterrupted stretches of rocky shore. Our results suggest that ecological barriers are not required to induce philopatric behavior in Variabilichromis, and that morphological stasis persists in the face of high levels of neutral genetic differentiation.     

Linearized oscillations in population dynamics

A linearized oscillation theorem due to Kulenović, Ladas and Meimaridou (1987,Quart. appl. Math. XLV, 155–164) and an extension of it are applied to obtain the oscillation of solutions of several equations which have appeared in population dynamics. They include the logistic equation with several delays, Nicholson's blowflies model as described by Gurney, Blythe and Nisbet (1980,Nature, Lond. 287, 17–21) and the Lasota-Wazewska model of the red blood cell supply in an animal. We also developed a linearized oscillation result for difference equations and applied it to several equations taken from the biological literature.     

Biometric relation between body size and otolith size of seven commercial fish species of the south‐western Atlantic

Given the importance and applicability of these biometric relations, the present work aimed to verify the existence of correlations between the length of saggitae otoliths and the body size of seven south‐western Atlantic marine fish species and to generate equations to estimate the body size of these species through otolith measurements. Fifty otoliths of Centropomus parallelus, Centropomus undecimalis, Lutjanus analis, Lutjanus jocu, Lutjanus synagris, Chaetodipterus faber and Mugil curema were collected for analysis. Significant relations between otolith length and total length and otolith width and total length were found for all the species. The highest coefficient of determination was observed for Centropomus undecimalis and Lutjanus synagris, for both relations, and the lowest was observed for Mugil curema. The results show that estimates of body size of the species through biometric analyses of otoliths are reliable. Based on this, the equations generated to obtain the total length of the fish using biometric otolith data can be used in dietary studies of top predators and in paleontological recostructions of modern fish.     

Body size evolution of a shell‐brooding cichlid fish from Lake Tanganyika

The substrate‐brooding cichlid fish Telmatochromis temporalis in Lake Tanganyika demonstrates a simple example of ecological speciation between normal and dwarf morphs through divergent natural selection on body size. The dwarf morph most likely evolved from the ancestral normal morph; therefore, elucidating the evolution of its small body size is a key to understanding this ecological speciation event. Previous studies suggest that the small body size of the dwarf morph is an adaptation to the use of empty snail shells as shelters (males) and spawning sites (females), but this idea has not been fully evaluated. Combining original and previously published information, this study compared likelihood values to determine the primary factor that would be responsible for regulating the body size of the dwarf morph. Male body size is most likely regulated by the ability to turn within shells, which may influence the predation avoidance of adult fish. Females are smaller than males, and their body size is most likely regulated by the ability to lay eggs in the small spaces within shells close to the shell apices where predation risk on eggs is lower. This study provides new evidence supporting the hypothesis that different natural selection factors affected body size of the different sexes of the dwarf morph, which has not been reported in other animal species.     

Schooling preferences for familiar fish vary with group size in a wild guppy population

The ability of fish to recognize and preferentially associate with familiar conspecifics has been well documented in a series of laboratory experiments. In this paper we investigate the schooling preferences of wild female guppies, Poecilia reticulata, in the Upper Tunapuna River in Trinidad and confirm that they do indeed prefer to associate with familiar individuals. The guppies in this river occur in a series of pools that become isolated during the dry season. These fish interact solely with other individuals in their pool for periods of several months at a time and thus have ample opportunity to become accustomed to one another. Our study also reveals that the tendency of female guppies to school with familiar fish declines as the group size in which they naturally live increases. Preferences are strong when there are small numbers of females in a pool, but diminish thereafter. This indicates that the expression of familiarity is constrained by group size. The basis of recognition and the consequences of schooling preferences for familiar individuals are discussed.     

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.     

Feeding of fish in Lake Glubokoe

Lake Glubokoe is inhabited by 13 species of fish. The commonest are roach, bream, perch and ruff. Comparison of seine catches for 1950 and 1984 revealed a considerable decrease in the share of perch (from 31% to 2%) and ruff (from 18.5 to less than 0.1%) in 1984. The richest food resource in the lake is crustacean plankton. In summer, it is mostly consumed by roach. Estimation of the electivity shows that, unlike perch, roach selectively consumes small crustaceans (Bosmina and Polyphemus). Poor growth rate of all common species of fish points to their food limitation. In summer the diets of common species of fish are differentiated to a considerable extent. Of 36 pairs of combinations a high food overlap was found only in 2 cases: 1) O + perch and Leucaspius delineatus, 2) yearlings and adult roach. Low diet overlap in fish during intensive feeding in summer probably reflects a feedback between the volume and intensity of food competition. The populations of bream and ruff probably compete for chironomid larvae which inhabit the sublittoral, as perch, roach and Leucaspius delineatus probably do for large littoral insects. However, intraspecific competition appears to be more important than interspecific for the roach and bream populations (the two most numerous species in the lake).     

Effective population size in the captive breeding program of the Lake Victoria cichlid Paralabidochromis chilotes

Microsatellite DNA markers were used to monitor levels of genetic variation in 3 generations of the American Zoo and Aquarium Association [AZA] Species Survival Plan [SSP] captive breeding program for the Lake Victoria cichlid Paralabidochromis chilotes. Temporal changes in the frequency of 15 alleles, across four polymorphic loci, were used to estimate effective population size (N_e). The upper limit of the 95% confidence interval for N_e never exceeded eight individuals, with all of the corresponding N_e/N ratios falling below 0.15. A test of the proportion of expected heterozygous individuals between the F₁ and F₃ generations indicated a significant decline in expected heterozygosity of 5% per generation. Alternative husbandry protocols, including subdividing the captive population, are addressed to reduce the further loss of genetic variation. Zoo Biol 18:215–222, 1999. © 1999 Wiley‐Liss, Inc.     

Multi-scale recruitment patterns and effects on local population size of a temperate reef fish

Recruitment of the temperate reef fish Coris julis was studied across the Azores Archipelago (central North Atlantic), over four consecutive recruitment seasons and at three spatial scales: between islands (separated by 100s of km), sites within islands (separated by 10s of km) and transects within sites (separated by 10s of m). At the largest scale ( i.e . between islands) spatial recruitment patterns were highly variable, suggesting the influence of stochastic processes. Recruitment was spatially consistent within islands, even though magnitude was unpredictable between years, indicating that processes at meso-scales are probably more deterministic. Recruits settled randomly at the transect scale, probably reflecting habitat homogeneity. It was proposed that large and island-scale patterns reflect larval availability, driven by physical and biological processes occurring in the plankton. No evidence was found for a density-dependent relationship between newly settled and 2 week settled C. julis nor between cumulative recruitment and young-of-the-year. It appears that adult density is limited by larval supply (pre-settlement regulation) at low recruitment sites, and determined by post-settlement, density-dependent processes at high recruitment sites. This work is one of few to investigate multiple spatial and temporal scales of recruitment for a coastal fish species inhabiting isolated, temperate oceanic islands and hence, provides a novel comparison to the many studies of recruitment on coral reefs and other, more connected systems.     

Experimental evolution in Heterandria formosa, a livebearing fish: group selection on population size

Group selection has historically been an important and controversial subject in evolutionary biology. There is now a compelling body of evidence, both theoretical and experimental, that group selection not only can be effective, but can be effective in situations when individual selection is not. However, experiments in which true population-level traits have been shown to evolve in response to group selection are currently limited to two species of flour beetle in the genus Tribolium and RNA viruses. Here we report the results of an experiment wherein we imposed group selection via differential extinction for increased and decreased population size at 6-week intervals, a true population-level trait, in the poeciliid fish Heterandria formosa. In contrast to most other group selection experiments, we observed no evolutionary response after six rounds of group selection in either the up- or down-selected lines. Populational heritability for population size was low, if not actually negative. Our results suggest that group selection via differential extinction may be effective only if population sizes are very small and/or migration rates are low.     

The land/inland-water ecotones and fish population of Lake Valley (West Mongolia)

New data on fish populations of a closed desert watershed of Mongolia were obtained in 1990 and 1991. For this region periodic droughts, with the accompanying disappearance of lakes and some parts of rivers, are typical. Two forms of a Cyprinid species Oreoleuciscus humilis (dwarf Altai osman) occur in this region during wet periods which usually last for 10-30 years. The dwarf form, is characterized by a maximum SL of 200 mm and early maturation (SL = 70 mm, four years of age). It inhabits small desert rivers in dry periods which last for 3–5 years and both rivers and the riparian zone of lakes during wet periods. The larger lake form occurs only in lakes during the wet periods. It can attain a maximum size of 450 mm and matures in six years, SL = 200 mm. These two forms of O. humilis differ in feeding habits, rates of growth, and morphology. The dwarf form feeds mainly on insect larvae and on plants. The lake form consumes the same food items until it reaches 180 mm SL and then becomes piscivorous. Populations of O. humilis in lakes are restored after a dry period, originating anew from river populations of the dwarf form.Currently there is a transition from a dry period to a wet one. Orog-Nur (one of the lakes of Lake Valley) has been filling with water since 1990. In July 1991 the depth of this lake reached 0.5–1.0 m and fish were found in the lake. The large individuals of dwarf form which came to the lake from the Tuyn-Gol River became cannibals, and their growth rate increased rapidly. The homogeneous environment and low food supply in the restored lakes are suggested to be the main causes of these phenomena.