Growth of Bream,Abramis brama L., in Two Outside Basins of Different Trophic State of Lake Balaton

Age-composition, size-distribution, length/weight relationships and growth both in length and weight of bream stocks were studied on fishes collected in NE and SW basins of Lake Balaton during 1982/83. Stocks consisting of 10 to 12 age-groups were observed at the two lake areas. The linear growth and weight-gain in the SW-basin were annually faster than in the NE-basin, however, the growth of bream in Lake Balaton was slow as compared to that observed 10 years ago. Parallel with progressive eutrophication, the density of bream stocks increased by some 5–10 % especially at hypertrophic lake areas (SW) and consequently their growth was transformed to densitydependent. In the appearance of strong year-classes some cyclicism could be observed especially in the SW-basin.     

First Year Ontogenetic Diet Patterns in Two Coexisting <Emphasis Type="Italic">Sander</Emphasis> Species, <Emphasis Type="Italic">S. lucioperca</Emphasis> and <Emphasis Type="Italic">S. volgensis</Emphasis> in Lake Balaton

First year ontogenetic diet patterns and size-dependent diet partitioning of two coexisting piscivorous percids, pikeperch and Volga pikeperch were analysed in Lake Balaton. Diet patterns of the two pikeperches followed a common trend, catching larger preys at larger sizes, but in details they were different. Until 20–30 mm size age-0 pikeperch fed on planktonic microcrustaceans and were found only in the pelagic zone. After this size, from the end of May, a part of the stock shifted habitat and moved to the littoral zone to feed on Limnomysis benedeni. Majority of the stock stayed in the pelagic zone and shifted to Leptodora kindtii. In the pelagic group early piscivory, mainly cannibalism, occurred only sporadically. However, the few individuals that reached 100 mm size during the first year were typically piscivorous. Volga pikeperch stayed in the pelagic zone during the first year and shifted from planktonic microcrustaceans to benthic macroinvertebrates. General patterns of the first year diet ontogeny were similar in the different areas of Lake Balaton in both pikeperches with only some differences in the secondary food resources, especially in the share of chironomids. Chironomids were eaten at highest ratio by the two fish species in the Keszthely basin in accordance with their abundance pattern. Maximum prey sizes increased significantly with predator size in both pikeperch and Volga pikeperch. However, pikeperch ate much larger prey than did Volga pikeperch at the same size although they have a similar mouth gape to length ratio. These two, closely related pikeperches, although occur in the same habitat and have similar patterns of diet ontogeny, effectively partition food resources in Lake Balaton during the first growing season, except in the very beginning of their ontogeny at L = 5–10 mm size. It appears that age-0 Volga pikeperch is not a significant competitor for the economically highly rated pikeperch in Lake Balaton. On the other hand, it is age-0 pikeperch that might affect Volga pikeperch during its early ontogeny, in the planktivorous stage.     

Habitat shift in roach (Rutilus rutilus) induced by pikeperch (Stizostedion lucioperca) introduction: predation risk versus pelagic behaviour

Changes in the fish community structure and habitat use were followed after the introduction of pikeperch (Stizostedion lucioperca) to the roach-dominated Lake Gjersjøen. Quantitative echosounding showed that the density of juvenile roach (Rutilus rutilus) was dramatically reduced in pelagic areas, from 12 000–15 000 fish/ha to 250 fish/ha, while total fish density remained unchanged in littoral areas. At the same time, the habitat segregation between different size groups of roach was altered as larger roach utilized the pelagic zone after pikeperch introduction. The loss of the pelagic refuge for juvenile roach increased the availability of juvenile roach to littoral predators, notably perch. In littoral areas, the fish community changed from one dominated by roach (> 95%) to one dominated by perch (> 50%).     

Paleolimnological reconstruction of the trophic state in Lake Balaton (Hungary) using Cladocera remains

The sediment of Lake Balaton (Hungary) provides important information about the lake’s history, particularly with regard to eutrophication. In this study, we used fossil pigment analysis and subfossil Cladocera remains preserved in a dated sediment core to identify trophic stages from ~250 bc to present. Dates of the most recent eutrophic events are in good agreement with previously published data. In general, the abundance and diversity of the Cladocera community increased with eutrophication and decreased with oligotrophication. The sediments of Lake Balaton were characterised by Chydoridae remains, of which Alona species were the most abundant. Of these, Alona quadrangularis and Alona affinis accounted for 40 and 20% of the total Cladocera remains, respectively. The trophic state of Lake Balaton varied between mesotrophic and eutrophic regimes. Seven different trophic periods were identified in Lake Balaton on the basis of Sedimentary Pigment Degradation Unit (SPDU) content of the sediment. Eutrophic states were (1) from ~250 to ~30 bc, (3) between ~300 and ~590 ad, (5) between 1834 and 1944 and (7) from the 1960s until present. Mesotrophic states were (2) ~30 bc to ~300 ad, (4) 590–1834, (6) 1944–1960s. Discriminant analysis of the cladoceran data confirmed these historic events, except for the short mesotrophic episode between 1944 and 1960. The first stage of eutrophication of Lake Balaton (~250 to ~30 bc) was characterised by extensive macrophyte vegetation, as indicated by the increasing abundance of vegetation-associated Cladocera species (Eurycercus lamellatus, Sida crystallina, Pleuroxus sp.). Intensification of eutrophication was identified since the 1980s, reflected by a high abundance of Bosmina species. The most significant planktivorous fish of Lake Balaton was the Sabre carp (Pelecus cultratus), and when its number decreased, the abundance of Bosmina species increased. This study shows that Cladocera are responsive to trophic state changes, underlining their importance as a tool for the assessment of lake eutrophication.     

香根草形态性状和光合特性对三峡库区消落带水陆生境变化的响应

基于定位观测,研究三峡库区消落带淹水区和未淹区香根草的形态性状、生物量、光合参数和资源利用效率,并对其适应机制进行讨论。结果显示:(1)香根草可以在消落带每年淹水期4个月左右、淹水深度小于9m的海拔区段存活。(2)淹水区香根草的地上部分多数形态性状指标较未淹区有所降低,降低幅度随香根草露出水面恢复生长的时间长短而异。(3)淹水区香根草总生物量、地上部分生物量分别减少10.58%、48.46%,而根径、根系长度、根系数量、根幅、地下生物量以及地下/地上生物量的比值分别提高12.50%、24.13%、19.09%、78.46%、30.04%、151.71%;同期香根草的蒸腾速率、气孔导度和胞间CO2浓度分别减少20.75%、9.19%和10.04%,而净光合速率、水分利用效率、表观CO2利用效率分别提高7.23%、36.47%和63.64%。研究表明,加速根系分蘖和生长、增加叶片长度和地下生物量,降低植株高度、减少蒸腾、提高水分和CO2利用效率是香根草对三峡库区消落带水陆生境变化的适应对策。     

Population structure and feeding characteristics of Volga pikeperch,Sander volgensis (Pisces,Percidae), in Lake Balaton

Hydrobiologia - Growth, population structure, abundance, production, and feeding of Volga pikeperch were studied in Lake Balaton. The population was mainly comprised of age-groups 0+ (59%) and 1+...     

Size-independent growth in fishes: patterns, models and metrics

A combination of a dynamic energy budget (DEB) model, field data on Atlantic salmon Salmo salar and brown trout Salmo trutta and laboratory data on Atlantic salmon was used to assess the underlying assumptions of three different metrics of growth including specific growth rate (G), standardized mass‐specific growth rate (G_S) and absolute growth rate in length (G_L) in salmonids. Close agreement was found between predictions of the DEB model and the assumptions of linear growth in length and parabolic growth in mass. Field data comparing spring growth rates of age 1+ year and 2+ year Atlantic salmon demonstrated that in all years the larger age 2+ year fish exhibited a significantly lower G, but differences in growth in terms of G_S and G_L depended on the year examined. For brown trout, larger age 2+ year fish also consistently exhibited slower growth rates in terms of G but grew at similar rates as age 1+ year fish in terms of G_S and G_L. Laboratory results revealed that during the age 0+ year (autumn) the divergence in growth between future Atlantic salmon smolts and non‐smolts was similar in terms of all three metrics with smolts displaying higher growth than non‐smolts, however, both G_S and G_L indicated that smolts maintain relatively fast growth into the late autumn where G suggested that both smolts and non‐smolts exhibit a sharp decrease in growth from October to November. During the spring, patterns of growth in length were significantly decoupled from patterns in growth in mass. Smolts maintained relatively fast growth though April in length but not in mass. These results suggest G_S can be a useful alternative to G as a size‐independent measure of growth rate in immature salmonids. In addition, during certain growth stanzas, G_S may be highly correlated with G_L. The decoupling of growth in mass from growth in length over ontogeny, however, may necessitate a combination of metrics to adequately describe variation in growth depending on ontogenetic stage particularly if life histories differ.     

Biomass of planktonic crustaceans and the food of young cyprinids in the littoral zone of Lake Balaton

The littoral zone of Lake Balaton and its periphyton-zooplankton-fish communities have been investigated intensively in recent years. Total average number of crustacean plankton varied from 36 to 126 ind l^–1, their biomass from 0.49 to 1.86 mg ww l^–1 month^–1 at different areas of the littoral zone. In general, these values for the above parameters were higher in hypertrophic areas. 23 fish species occurred in the littoral zone with cyprinids dominating. The seasonal food spectra of Y-O-Y roach (Rutilus rutilus), white bream (Blicca bjoerkna) and bream (Abramis brema) were based mainly on planktonic crustaceans and benthic/periphytic invertebrates. According to the frequency of occurrence of crustaceans and other invertebrates, the food composition of young cyprinids differed significantly in the NE and SW-basins of the lake.     

Assessment of exploited fish species in the Lake Edward System,East Africa

The unknown status of inland fish stocks hinders their sustainable management. Therefore, increasing stock status information is important for sustainable inland fisheries. Fisheries reference points were estimated for five exploited fish species (11 stocks) in the Lake Edward system, East Africa, which is one of the most productive inland water systems. The aim was to ascertain the status of the fisheries and establish reference points for effective management. The reference points were based on four linked stock assessment approaches for data-limited fisheries. Estimates showed poor stock status with the stocks defined as either collapsed, recruitment impaired or overfished. However, higher catches could be obtained under sustainable management. Estimates of maximum sustainable yield (MSY) and supporting biomass (B_msy) are provided for 10 of the stocks as targets for rebuilding plans. The immediate target of management should be rebuilding biomass to B_msy. Applicable measures include shifting length at first capture to the length that maximizes catch without endangering size structure and biomass, and livelihood diversification out of fisheries.     

Population parameters and exploitation rate of Sarotherodon galilaeus galilaeus (Cichlidae) in Lakes Doukon and Togbadji,Benin

Growth, mortality, recruitment and relative yield per recruit of Sarotherodon galilaeus galilaeus from Lakes Doukon and Togbadji were studied. Data on total length, total weight and sex were recorded on a monthly basis between January and December 2013 for S. g. galilaeus captured by local fishers. The estimated asymptotic lengths L_∞ were 26.2 and 23.6?cm for Lakes Doukon and Togbadji, respectively, while the growth rate K was 0.73 in Lake Doukon and 0.87 in Lake Togbadji. Estimates of fishing mortality, 0.27 and 0.47 y^?1 for Doukon and Togbadji, respectively, were low relative to natural mortality, 1.51 and 1.74 y^?1, respectively. Sizes at first sexual maturity were 12.8 and 13.2?cm for females and males, respectively, in Lake Doukon, and 11.5 and 12.4?cm for females and males, respectively, in Lake Togbadji. The size at first capture was estimated at 13.3 and 12.7?cm for Lakes Doukon and Togbadji, respectively, which, in the light of the size at maturity estimates, indicates that fish spawn at least once before capture. The current exploitation rates of 0.15 for Lake Doukon and 0.21 for Lake Togbadji suggest that their stocks of S. g. galilaeus are not overexploited in either lake.     

Calculation of Fluctuating Asymmetry of the biggest Caspian whipsnake population in Hungary compared to a common snake species

The Fluctuating Asymmetry (FA) is a special type of asymmetry in the populations of bilaterally symmetrical creatures. The FA gives us numerical data on the developmental instability of the populations and refers to potential genetical and environmental stressors affecting the populations. Here we give the first data on the FA of the protected Caspian whipsnake (Hierophis caspius) from Hungary. The FA indices of the biggest population from Villány Mts were compared to the FA indices of two differently stressed Dice snake (Natrix tessellata) populations [stressed (Mád) and seminatural (Lake Balaton)]. Based on the values of the multiple and the simple indices derived from sublabial scales, we can say that the status quo of the highly protected Caspian whipsnake population does not represent significant deviation from the near-natural dice snake population from the Lake Balaton.     

Growth and length–weight relationships of Sander lucioperca (Linnaeus, 1758) in the Alcántara Reservoir,south‐western Spain: comparison with other water bodies in Eurasia

Growth parameters in pikeperch may be affected by several factors. The purpose of this study was to investigate the growth and length–weight of pikeperch in a reservoir in south‐western Spain and compare the results with previous published data. Age and growth are described for Sander lucioperca from the Alcántara Reservoir (south‐western Spain) from March to October 2009. A total of 285 fish were examined; the ratio of males to females was estimated as 0.78:1 and age ranges as 1–5 years. Total lengths ranged from 16.1 to 52.5 cm. The length–weight relationships were described as W = 0.00 462 TL^3.09 (r = 0.9865) for males and W = 0.00279 TL^3.16 (r = 0.9921) for females. Growth was expressed in length and the von Bertalanffy growth parameters were estimated as L∞ = 92.14 cm, k = 0.09, t₀ = ?1.05 for males and L∞ = 107.72 cm, k = 0.08, t₀ = ?1.16 for females. Growth performance indexes were also estimated as Φ’ = 2.88 for males and Φ’ = 2.96 for females. Differences in growth and length–weight relationships between sexes were not found.     

Dynamics and ecological significance of daily internal load of phosphorus in shallow Lake Balaton, Hungary

1. As supported by field data, turbidity recorded by light scattering sensors could reliably be converted into concentration of suspended particulate matter (SPM) and coefficient of vertical light attenuation (K_d) in Lake Balaton. 2. Autocorrelation analysis revealed that proper determination of SPM concentration and K_d required daily sampling. To approximate daily rate of resuspension, 15 min or more frequent measurements were needed. Thus, routine monitoring provides very little insight into environmental variability of shallow lakes as habitats for phytoplankton. 3. The internal P load was estimated from daily rate of resuspension and P desorption capacity of sediments. The latter was assumed to be proportionate to the potentially mobile inorganic P content of SPM. A comparison with net primary production and nutrient status of phytoplankton showed that the proposed method of estimating time series of internal P load captured seasonal trends. 4. The daily rate of resuspension was high whereas that of internal P load was low in Lake Balaton relative to other shallow lakes. The latter reflects favourable behaviour of the calcite‐rich sediments. As a consequence, carrying capacity of Basin 1 of Lake Balaton was P‐determined. 5. The timing of external and internal loads was radically different. While the former showed mostly seasonal changes, large pulses characterised the latter. As a consequence, internal load may supply more P to phytoplankton growth during the critical summer months than external load. However, the relative importance of these sources may show substantial interannual variability. 6. Large resuspension events often followed each other during periods of 10–15 days. It has been shown that disturbances in this frequency range are of key importance in maintaining the diversity of phytoplankton. We propose that resuspension can be perceived not only as a disturbance factor but also as a factor that periodically relaxes nutrient stress. The former feature may dominate the instantaneous effect, whereas the latter may determine the persistent effect of resuspension on succession of phytoplankton.     

The Availability of Condensed Phosphates for the Algal Strain Scenedesmus obtusiusculus Chodat,with Special Regard to Conditions Characteristic in Lake Balaton

The limiting factor in the water of Lake Balaton was calculated by means of Verduin's equation. If only the orthophosphate-phosphorus concentration is inserted into the equation, phosphorus is the primary limiting factor. If, however, total phosphorus is considered, the factor intensity of nitrogen will be the least, i. e. nitrogen will be the primary limiting-factor of plant growth. According to measurements during 1976, average values for the total dissolved phosphorus and orthophosphate-phosphorus content of Balaton Lake water were 15,66 mg/m³ and 7.66 mg/m³, respectively. Experiments with the algal strain Scenedesmus obtusiusculus Chod. (Chlorophyceae, Chlorococcales). were designed to test the availability of the condensed phosphorus form for the algae. The experiments were performed partly with synthetic polyphosphates, partly, with polyphosphates isolated from Balaton Lake water. The results showed, contrary to our expectations, that phosphates present in the condensed form (irrespective of their structure and degree of condensation). were not utilized by the algae under sterile conditions, i. e. in the absence of bacterial activity. In the light of the above it is recommended to consider only orthophosphate-phosphorus when calculating the limiting factor.     

Adenosine A1 Agonists and the Ca2+ Channel Agonist Bay K 8644 Produce a Synergistic Stimulation of the GTPase Activity of Go in Rat Frontal Cortical Membranes

Abstract: The identity and role of G proteins in coupling adenosine receptors to effectors have been studied to a limited degree. We have identified the G proteins whose GTPase activity is stimulated by adenosine receptor agonists in neuronal membranes. (R)-Phenylisopropyladenosine, 2-chloroadenosine, and N-ethylcarboxamideadenosine produced a concentration-dependent stimulation of GTPase. At 10^?5M, the increase above basal GTPase in frontal cortex was 25 ± 4, 20 ± 3, and 8 ± 1%, respectively, and in the cerebellum 55 ± 2, 41 ± 4, and 22 ± 2%, respectively. The effects of (R)-phenylisopropyladenosine and 2-chloroadenosine were inhibited by (1) A₁ antagonists (76–96% reduction), (2) pretreatment with pertussis toxin (90–100% reduction), and (3) antibodies raised against the α-subunit of G_i and G_o (55–57% reduction by each), suggesting that A₁ receptors interact equally with G_i and G_o. (R)-Phenylisopropyladenosine increased the binding of a nonhydrolyzable analogue of GTP to membranes in a pertussis toxin-sensitive manner, indicative of activation of G_i or G_o. Previously, (±)-Bay K 8644 enhanced GTP hydrolysis by G_o but not G_i. Now we report a profound synergistic stimulation of GTPase in the presence of (R)-phenylisopropyladenosine and (±)-Bay K 8644 (10^?7 to 10^?5M). (±)-Bay K 8644 had no effect on nucleotide exchange and, thus, cannot activate G_o. It appears that a positive cooperative stimulation of G_o occurs when it is first activated by A₁ receptors and subsequently interacts with the L-type Ca²⁺ channel.     

Relationships between opercula girth, maximum girth and total length of fish species caught in gillnet and trammel net selectivity surveys off the Portuguese coast

The relationships of total length (L_t) to girth at opercula (G_ope) and maximum girths (G_max) were estimated for 39 and 22 fish species, respectively, captured off the Portuguese coast between Póvoa do Varzim and Santo André (38°05′54′′–41°15′36′′N and 8°46′54′′–9°31′13′′W). The data were collected between April 1994 and September 1995. The best‐represented family was Sparidae (five species), followed by Soleidae and Triglidae (four species each). G_ope and G_max were found to increase linearly with length for all species, all r² values being statistically significant (P < 0.01) and higher than 0.81. When G_ope and G_max were plotted against length for all species combined, three groups were identified, corresponding to general girth–length relationships: G1 = 1.408 + 0.238 ×L_t, G2 = 2.455 + 0.328 × L_t and G3 = ?0.72 + 0.60 × L_t for opercula girth and G1 = 3.402 + 0.195 × L_t, G2 = 2.211 + 0.374 × L_t and G3 = ‐2.514 + 0.717 × L_t for maximum girth. These groups correspond to different body shapes of fishes: G1‐round, G2‐torpedo‐form and G3‐compressed body.     

Growth parameters and total mortality in Oreochromis niloticus (Linnaeus) from Nyanza Gulf,Lake Victoria

Length-frequency data collected from fish landings in the Kenya waters of Lake Victoria were used to estimate the growth parameters, total mortality rate and growth performance index in Oreochromis niloticus. The asymptotic length, (L _∞) and the ratio of the total mortality rate (Z) to the growth constant (K), were estimated to be 64.6 cm and 3.219 respectively. K was 0.254 y^-1, Z was 0.818 y^-1 and the growth performance index θ′ = Log₁₀ K + 2 log₁₀ L∞ = 3.025, which is rather high as compared to other tilapia populations in natural waters.     

Eutrophication as a driver of r‐selection traits in a freshwater fish

This study tested whether eutrophication could influence life‐history traits of a cyprinid, Chanodichthys erythropterus, in 10 Chinese lakes. Using the von Bertalanffy growth model, the asymptotic length (L_∞) and the growth performance index (I_GRO) were significantly affected by eutrophication. The gonado‐somatic index (I_G) and relative fecundity (F_R) were significantly lower in mesotrophic lakes than in eutrophic and hypertrophic lakes. These results indicate that increasing eutrophication affects the life‐history tactics of a freshwater fish.     

PRODUCTION OF THE AFRICAN CATFISH (CLARIAS GARIEPINUS) I. GROWTH,MORTALITY AND YIELD SOUTH OF THE ZAMBEZI

SUMMARY

Clarias gariepinus were sampled from eight water bodies in southern Africa between 1973 and 1975. Aging results indicate a similar growth pattern for most areas with a near linear age-length relationship. Between year growth compensation was found to be present in Lakes Kyle and Mcllwaine in Zimbabwe, and to a lesser extent in Hardap Dam, South West Africa, but not present in Lake Kariba, Zimbabwe.

The fishable biomass of catfish from Lake Kyle is estimated between 0,61 to 1,14 kg ha^?1. Fishable biomass for all species is in the range 12,1 to 22,7 kg ha^?1.

The instantaneous growth rate was found to be between 0,20 and 0,25 for fully recruited age groups. The fishing mortality appears to be in the range of 0,4 for Lakes Kyle and Kariba and 0,5 for Lake McIlwaine. All of these levels are above the yield per recruit F₀, 1 levels of 0,27, 0,28 and 0,24 respectively which would normally indicate that each of these stocks is being overexploited. However, this does not appear to be the case in these tropical impoundments.