Temporal variation in fish community structure in a newly created wetland lake (Lake Agmon) in Israel

Lake Agmon was constructed in summer 1994 in the northern part of the drained Lake Hula swamp, as part of the Hula Reclamation Project. One of the main goals of the project was to attract aquatic and semi- aquatic birds to the area as a basis for planned eco-tourism and one of the main concerns of the project was the potential for increased proliferation of mosquitoes (including vector species of malarial parasites). There was a perceived need, therefore, to establish and maintain a suitable fish community. This present study documents the developments in the fish community in Lake Agmon between May 1995 and December 1996. The lake was initially stocked with two fish species, Tilapia zillii and Gambusia affinis, to control mosquitoes and to provide suitable small- bodied forage species for piscivorous birds. Subsequent stocking also included Oreochromis aureus, and Cyprinus carpio. Additional species were established by immigration from the Jordan River. Relatively large species ( e.g., Clarias gariepinus and C. carpio) flowed into the lake as eggs or juveniles, whereas the smaller species ( e.g., Hemigrammocapoeta nana, Pseudophoxinus kervillei and Aphanius mento) entered the lake as adults. In the first year, eight fish species were found in Lake Agmon: T. zillii, G. affinis, C. gariepinus, C. carpio, Capoeta damascina, P. kervillei, Acanthobrama lissneri and H. nana. Of these, T. zillii, G. affinis and H. nana were dominant, though the relative abundance of H. nana was very low in spring, and increased during summer. In the second year, O. aureus, A. mento and Anguilla anguilla also occurred in the lake. The density of P. kervillei increased, in comparison with the previous year. The relative proportions of juvenile and adult fish also changed in the second year. A high percentage of young T. zillii was found during the first spring, decreasing in the summer and autumn. The proportion of juveniles of both G. affinnis and H. nana was very low during the first year, but increased during the second. These results indicate that the fish community of Lake Agmon had not stabilized by the end of 1996 and that further changes in relative abundances, and species, age and sex compositions should be expected.     

Differential infectivity of Transversotrema patialense for naive fish

The discovery of Transversotrema patialense cercariae in an aquarium harboring tropical fish triggered the present study. The purpose was to estimate the potential range of infection of local freshwater and fishpond populations by T. patialense. Experimental infection of T. patialense differed among 3 species employed: 76.5% for Tilapia zillii, 37.8% for Gambusia affinis, and none for 2 varieties of Cyprinus carpio. These patterns of infectivity are different from those published previously for T. patialense infections, and they may be attributed to the origin of the fish (temperate water vs. tropical and subtropical waters) and the size of their scales. In G. affinis, but not in the other species, worm load and fish length were closely related, and the left side harbored heavier worm burdens than the right side. Taken together, these results suggest that imported T. patialense may spread to various indigenous natural and cultured fish populations, with ensuing potential harm to these populations.     

Food habits of three carnivore species (Viverricula indica, Herpestes urva, and Melogale moschata) in Fushan Forest, northern Taiwan

The food habits and degrees of dietary overlap of lesser oriental civet ( Viverricula indica ), crab-eating mongoose ( Herpestes urva ), and ferret badger ( Melogale moschata ) inhabiting the Fushan Forest, northern Taiwan, were studied using faecal analysis between February 1993 and June 1994. Laboratory analysis of 154 civet faeces, and 174 mongoose faeces showed that both species fed on a wide variety of food items, including mammals, birds, reptiles, amphibians, fish, crustaceans, insects, oligochaetes, gastropods, chilopods, arachnids, and plants. Insects, oligochaetes, plants, and mammals were the four most important food items in the civets' diet, whereas crustaceans, insects, amphibians, and reptiles were the four most important food items consumed by mongooses. Amphibians were the only vertebrates, together with invertebrates and plants, found in the 64 ferret badger faeces we analysed, and oligochaetes, insects, and amphibians were the most important food items consumed by ferret badgers. The diversity of diet was highest in the mongoose, followed by the civet, and was lowest in the ferret badger.
The degree of dietary overlap was greatest between the civet and the ferret badger, followed by that of the civet and mongoose. The mongoose and ferret badger had the lowest degree of dietary overlap. However, the degree of dietary overlap varied in different seasons. Invertebrates were the most important food source for the carnivores in Fushan Forest.     

The food and feeding habits of Physailia pellucida and Schilbe mystus with notes on the diets of S. uranoscopus and Siluranodon auritus, family Schilbeidae (Osteichthyes: Siluriformes) in Lake Kainji, Nigeria

SUMMARY. The food and feeding patterns of four schilbeids in Lake Kainji were studied between November 1974 and October 1975. Physailia pellucida , a small but abundant species, fed on small crustaceans and immature insects, while Schilbe mystus , a larger but less common schilbeid, fed principally on fish, with insects as a supplementary item in its diet. The rare species, Schilbe uranoscopus , was piscivorous, Siluranodon auritus , another small and rare species, is a herbivore feeding mainly on algae, with some crustaceans and immature insects taken as a source of animal protein. Preferential food selection by different length groups was found in S. mystus and P. pellucida . There were seasonal changes in the dietary items. Competition for food within the family was assumed not to occur in view of the different feeding habits of the species.     

An experiment on the culture of Tilapia esculenta (Graham) and Tilapia zillii (Gervais) (Cichlidae) in fish ponds

Segregated populations of Tilapia zillii and Tilapia esculenta were kept in artificial ponds. Supplementary food was given and phytoplankton was encouraged by the addition of superphosphate and ammonium sulphate fertilisers. The fry were cropped regularly in an attempt to control population size. A control population of T. zillii was also established in which none of these procedures were carried out.
The growth of T. esculenta was found to be dependent upon the phytoplankton density of the pond whilst T. zillii successfully utilized the supplementary food and grew well. The T. esculenta population also produced more fry than the T. zillii population. The comparative advantages of planktrvorous/brooders and herbivorous/guarders in fish culture are considered.
Despite the fecundity of the species used a population of known composition was maintained by manual cropping of the fry.
The addition of ammonium sulphate to the ponds caused blooms of phytoplankton which in turn had effects upon the base reserves and pH of the water, and probably caused some reduction of oxygen concentration beneath surface scums. This last point is used to explain the changes in phosphate and calcium content of the water also observed.
The low oxygen concentration frequently noted in the mornings probably affected the feeding behaviour of the fishes, and was low enough to have affected metabolism directly.     

Food and feeding habits of Ilisha africana (Bloch) (Pisces: Clupeidae) off the Lagos coast, Nigeria

A total of 2215 specimens of Ilisha africana (Bloch) were examined for the food habits of the species off the Lagos coast, Nigeria. Their food consisted mainly of crustaceans, fish and molluscs; less important in the stomach contents were insects, annelids, chaetognaths, coelenterates, urochordates and phytoplankton. The incidence of nematodes in the stomachs was low. Monthly variation of food as well as variation with fish size and water depth were examined, as was the relationship of food composition to components of the plankton fauna. Feeding habits of I. africana were compared with those Sardinella maderensis (Lowe), Galeoides decadatylus (Bloch), Brachydeuterus auritus (Val.) and Vomer setapinnis (Mitchill); there was an overall diversity in the diets of these fish species.     

Seasonal succession of zooplankton in the north basin of Lake Biwa

To examine the seasonal succession of the entire zooplankton community in Lake Biwa, zooplankton biomass (on an areal basis) and its distribution patterns among crustaceans, rotifers and ciliates were studied in the north basin from April 1997 to June 1998. Seasonal changes in phytoplankton and population dynamics of Daphnia galeata were also examined to assess food condition and predation pressure by fish. From March to November, crustaceans dominated zooplankton biomass, but rotifers and ciliates were dominant from December to February. Among crustaceans, Eodiaptomus japonicus was the most abundant species, followed by D. galeata. Zooplankton biomass increased from January to a peak in early April, just before the spring bloom of phytoplankton, then decreased in mid-April when mortality rate of D. galeata increased. From mid-June, zooplankton increased and maintained a high level until the beginning of November. During this period, both birth and mortality rates of D. galeata were relatively high and a number of rotifer and crustacean species were observed. However, their abundances were very limited except for E. japonicus which likely preys on ciliates and rotifers. In Lake Biwa, food sources other than phytoplankton, such as resuspended organic matter from the sediments, seems to play a crucial role in zooplankton succession from winter to early spring, while zooplankton community seems to be regulated mainly by fish predation from summer to fall.     

Manipulation of the Pelagic Food Web by Stocking with Predacious Fishes

Two water bodies, which are quite different with respect to nutrient load and hydrophysical conditions, are used to perform long-term experiments in the whole water on the manipulation of the pelagic food web. Experimental water 1: Bautzen Reservoir (Dresden County, GDR); hypereutrophic, mean depth=7.4 m; extremely exposed to wind. Experimental water 2: Small pond in a former quarry (Dresden County); mesotrophic; mean depth=7.0 m; extremely protected against wind. Only the results of Experiment 2 are given in detail. Experiment 1 is not yet finished. Experimental water 2 was investigated in 1979 and 1980 when no predatory fish species were present, and in 1981 after introduction of predators (mainly Salmo gairdneri). The response of the ecosystem can be summarized as follows: (1) The biomass of the zooplankton-eating fish (mainly Leucaspius delineatus) decreases rapidly. (2) The biomass of the herbivorous zooplankton increases to nearly 400%. (3) This finding reveals that the dense population of an invertebrate predator (Chaoborus flavicans) is not able to compensate for the feeding pressure of the small fish. But the intensive feeding activity of the young larvae of Chaoborus leads to a strong increase (200 to 300%) in the mean individual body size of the crustaceans during late summer and autumn, which supports the “balanced predation hypothesis”. (4) The remarkable enhanced grazing pressure of the herbivorous zooplankton on the phytoplankton does not exert any effect on the total phytoplankton biomass. This result is interpreted as a consequence of growth limitation of the algae due to low nutrient (Fe, P) supply in that mesotrophic water body. But the phytoplankton composition does reveal a strong response to the enhanced grazing pressure. The Secchi depth increases as a consequence of this change in the phytoplankton composition. The conclusion is drawn that, when using biomanipulation as a means of water quality management, it is obviously necessary to take into account the complex interrelationships between fish stocks, predacious invertebrates, herbivorous zooplankton, phytoplankton as well as nutrient load and hydrophysical processes in the particular water.     

Temperature-induced changes of early development and yolk utilization in the African catfish Clarias gariepinus

Artificially fertilized eggs and yolk-sac larvae of a freshwater tropical/subtropical fish Clarias gariepinus receiving no external food were incubated at 22, 25 and 28° C until full yolk resorption. Developmental time, size and matter composition (CHNS-O Analyzer and ashing) were assessed at egg fertilization, hatching and yolk resorption; respiration was measured every 4–5 h. The course of acceleration of C. gariepinus embryonic developmental rate with temperature ( Q_{10 dev}) was compared over the temperature range to those of Cyprinus carpio and Oncorhynchus mykiss ; they differed greatly, but were similar when compared on the basis of effective temperatures specific to each fish. Specific growth rates for energy (88, 150 and 183% per day at 22,25 and 28° C, respectively) as well as the conversion efficiencies of egg energy (64, 71 and 68%, respectively) and protein (71, 78 and 76%, respectively) in C. gariepinus larval tissues were higher than those known for the endogenous feeding period of coldwater and temperate fish species. In C. gariepinus at the end of yolk resorption, the carbon percentage and caloric values of dry weight, size (in terms of dry matter, minerals, protein and energy per larva) and transformation efficiencies were lowest at 22° C, highest at 25° C and had slightly decreased at 28° C. A tentative mechanism which leads to the positive or negative response of body size to temperature over the viable temperature range is defined.     

Food habits of small fishes in a common reed <Emphasis Type="Italic">Phragmites australis</Emphasis> belt in Lake Shinji,Shimane, Japan

To clarify the feeding habits of reed fishes, the gut contents of 13 fish species collected in a Phragmites australis belt in Lake Shinji were examined. Six species showed ontogenetic and/or seasonal changes in food use patterns. Smaller individuals generally preyed on small planktonic items (e.g., calanoid and cyclopoid copepods) or small crustaceans (gammaridean amphipods), subsequently changing to other prey items (e.g., mysids and filamentous algae) with growth. The most important dietary items for the reed fish assemblage comprised planktonic copepods, gammaridean amphipods and mysids. However, the relative importance of these changed seasonally, gammaridean amphipods being the most important in autumn and winter, and planktonic copepods and mysids the most important in spring and in summer. Cluster analysis based on dietary overlaps showed that the reed fish assemblage comprised five feeding guilds (planktonic-copepod, mysid, gammaridean-amphipod, filamentous-algae, and detritus feeders). Of these, the three former guilds were the most abundantly represented, whereas detritivores were represented by a single species.     

Differential responses of size‐based functional groups to bottom–up and top–down perturbations in pelagic food webs: a meta‐analysis

We performed a meta‐analysis of 31 lake mesocosm experiments to investigate differences in the responses of pelagic food chains and food webs to nutrient enrichment and fish presence. Trophic levels were divided into size‐based functional groups (phytoplankton into highly edible and poorly edible algae, and zooplankton into small herbivores, large herbivores and omnivorous zooplankton) in the food webs. Our meta‐analysis shows that 1) nutrient enrichment has a positive effect on phytoplankton and zooplankton, while fish presence has a positive effect on phytoplankton and a negative effect on zooplankton in the food chains; 2) nutrient enrichment has a positive effect on highly edible algae and small herbivores, but no effect on poorly edible algae, large herbivores and omnivorous zooplankton in the food webs. Planktivorous fish have a positive effect on highly edible algae and small herbivores, a negative effect on large herbivores and omnivorous zooplankton, and no effect on poorly edible algae. Our meta‐analysis confirms that nutrient enrichment and planktivorous fish affect functional groups differentially within trophic levels, revealing important changes in the functioning of food webs. The analysis of fish effects shows the well‐described trophic cascade in the food chain and reveals two trophic cascades in the food web: one transmitted by large herbivores that benefit highly edible phytoplankton, and one transmitted by omnivorous zooplankton that benefit small herbivores. Comparison between the responses of food webs and simple food chains also shows consistent biomass compensation between functional groups within trophic levels.     

The effect of feeding habitats on dietary shifts during the growth in a benthophagous suction-feeding fish

Several mechanisms of fish ontogenetic dietary shifts, which have important ecological implications, have been proposed. We studied the mechanism of dietary shifts of a benthophagous fish Goniistius zonatus, focusing on the effect of foraging on calcareous algal mat, one of its main feeding substrates, through comparison between two local populations (Morode and Arakashi) with different feeding ecology. The studied fish (11-29 cm SL) fed on various kinds of small invertebrates inhabiting the substrates, using a suctorial feeding mode without visual discrimination towards individual prey. At Morode, gut contents of small fish consisted of more epifaunal and less infaunal organisms than those of large fish, that is, mainly small crustaceans in small fish, and many invertebrates other than crustaceans in large fish. By contrast, at Arakashi, gut contents consisted mostly of epifaunal crustaceans regardless of fish size, i.e., fish showing no dietary shifts. At Morode, G. zonatus took foods mostly from thick calcareous algal mat, whereas fish foraged mainly on thin algal mat and bare rocks at Arakashi, the difference being due to the local differences in the substrate component. The algal mat of Morode harbored much larger amount of infaunal animals than any substrates of Arakashi. At Morode, large fish more forcefully and deeply thrust the mouth into thick algal mat than small fish, and was likely to suck up more infaunal prey using great suctorial force. The comparison clearly indicates that the dietary shifts of G. zonatus at Morode resulted from size-related efficiency in straining foods from heterogeneous micro-topography of thick algal mat.     

Energy sources for aquatic animals in the Orinoco River floodplain: evidence from stable isotopes

Summary Stable carbon and nitrogen isotope ratios in autotrophs, aquatic invertebrates and fishes from the Orinoco River floodplain of Venezuela reveal that microalgae, including both phytoplankton and epiphytic (attached) forms, are predominant energy sources for many aquatic animals, even though aquatic vascular plants are much more abundant. Floating mats of the grass Paspalum repens and the water hyacinth Eichhornia spp. harbor particularly high densities of aquatic animals, but isotopic evidence indicates that few species are dependent on organic carbon originating from these plants. The stable isotopic evidence for the trophic importance of algae contradicts traditional interpretations of food webs in freshwater wetlands, which are generally thought to be based largely on detritus originating from vascular plants.     

Birth and Death Rates of a Littoral Filter Feeding Microcrustacean,Sida crystallina (Cladocera), in Cochran Lake,Michigan

Population changes of Sida crystallina, a filter feeding microcrustacean which attaches to aquatic macrophytes, were examined in Cochran Lake, Michigan during June and July, 1979. Population estimates were derived from organisms present in 10 samples of leaves of the water lily Nymphaea odorata collected every 3 days. Population densities of Sida responded both to food and predation by fish. Declines in average clutch size were associated with decreasing phytoplankton biomass and the increasing dominance of colonial green and blue-green algae, but were not significantly influenced by the densities of invertebrates on the plants. Largemouth bass fry (Micropterus salmoides) dramatically reduced the numbers of Sida and altered the age structure of the population in late June.     

Temporal and spatial variation in ecosystem metabolism and food web carbon transfer in a wet‐dry tropical river

1. High light availability and stable base flow during the dry season promote primary production in perennial rivers of the wet–dry tropics, in contrast to production during the wet season which is often limited by turbidity and scouring. The Mitchell River of northern Queensland (Australia) was studied to understand controls on aquatic production and respiration in the dry season in relation to spatial and temporal gradients of light and temperature. 2. At three sites along the river, whole‐ecosystem gross primary production (GPP) and respiration (ER) were measured from diel changes of dissolved oxygen using the open‐channel single station method. Using stable carbon and nitrogen isotope analysis, aquatic consumers and their potential basal food resources were also assessed to determine food web relationships at the beginning and end of the dry season. 3. Nutrient limitation of aquatic net primary production was implied from the oligotrophic conditions and high algal C:N ratios. Rates of GPP were comparable with other tropical and temperate rivers and were regulated by light availability. 4. Respiration rates were high and similar to other tropical and subtropical rivers. Up to 52% of temporal variation of ER was explained by temperature, while P/R was lowest at the downstream site. 5. Benthic algae were the major carbon source for primary and secondary benthic consumers (insects) in the dry season but not for higher consumers (fish and crustaceans). Despite high rates of ER, which were probably supported by decaying terrestrial C3 plant material, this carbon source was not identified as contributing to animal consumer biomass. 6. While benthic algal production in the dry season sustained benthic invertebrates, the importance of external subsidies of carbon along the river, probably from the floodplain, was emphasised for fish and large invertebrates, which evidently were feeding on carbon sources not present in channel waterholes during the dry season.     

Accumulation of mercury in estuarine food chains

To understand the accumulation of inorganic mercury and methylmercury at the base of the estuarine food chain, phytoplankton (Thalassiosira weissflogii) uptake and mercury speciation experiments were conducted. Complexation of methylmercury as methylmercury-bisulfide decreased the phytoplankton uptake rate while the uptake rate of the methylmercury-cysteine and -thiourea complexes increased with increasing complexation by these ligands. Furthermore, our results indicated that while different ligands influenced inorganic mercury/methylmercury uptake by phytoplankton cells, the ligand complex had no major influence on either where the mercury was sequestered within the phytoplankton cell nor the assimilation efficiency of the mercury by copepods. The assimilation efficiency of inorganic mercury/methylmercury by copepods and amphipods feeding on algal cells was compared and both organisms assimilated methylmercury much more efficiently; the relative assimilation efficiency of methylmercury to inorganic mercury was 2.0 for copepods and 2.8 for amphipods. The relative assimilation is somewhat concentration dependent as experiments showed that as exposure concentration increased, a greater percentage of methylmercury was found in the cytoplasm of phytoplankton cells, resulting in a higher concentration in the copepods feeding on these cells. Additionally, food quality influenced assimilation by invertebrates. During decay of a T. weissflogii culture, which served as food for the invertebrates, copepods were increasingly less able to assimilate the methylmercury from the food, while even at advanced stages of decay, amphipods were able to assimilate mercury from their food to a high degree. Finally, fish feeding on copepods assimilated methylmercury more efficiently than inorganic mercury owing to the larger fraction of methylmercury found in the soft tissues of the copepods.     

The responses of littoral invertebrates to eutrophication-linked changes in plant communities

The decay of submerged macrophytes in lakes of high trophic level drastically limits the extent of habitat available to littoral invertebrates. The loss can be partially compensated by growth of filamentous algae. Our results show that macroinvertebrates typically associated with submerged macrophytes as well as planktonic crustaceans and rotifers occurred within algal mats at high densities.Aggregations of filamentous algae are usually short-term, with frequent appearances and disappearances. The rate of colonization of algal mats by invertebrates is rapid. In locations with a high degree of water exchange, animals colonize both living and decomposing algal mats at a similar rate, but in sheltered habitats, decomposing filamentous algae are colonized by a smaller number of animals.Comparison was made between the occurrence of invertebrate macrofauna on Chara spp., Potamogeton perfoliatus, P. lucens and Myriophyllum spicatum in several lakes. Although these macrophytes differ visibly in morphology and phenology, the number and composition of macroinvertebrates during summer was associated more closely with trophic state of a lake than with plant species.     

Changes in the plankton community following introduction of filter-feeding planktivorous fish

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter-feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined.
2. During a summer experiment, a bloom of Anabaena flos-aquae developed (≈ 8000 cells mL⁻¹) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700–14 400 organisms L⁻¹) after the bloom in this fish-free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass.
3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (≈ 24 °C) inhibited active feeding of this warm-water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans.
4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.     

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).     

Diet of bluegill Lepomis macrochirus in a South African reservoir during winter and summer

Alien fishes are considered a major threat to aquatic biodiversity in South Africa, yet relatively little regional information on their biology and ecology is available for many of these species. Seasonal changes in the diet of the bluegill Lepomis macrochirus in Howieson’s Poort Dam, Grahamstown, were assessed during summer and winter in 2014–2015, using stomach content analysis. In winter, juvenile and adult fish diets were dominated by crustacean zooplankton and insects, respectively. In summer, juvenile fish fed on crustaceans and insects, whereas adults consumed mostly fish eggs, indicating a potential impact by these invasive fish on native fish through oophagy.