Inspection and evaluation of host plant by the butterfly Mechanitis lysimnia (Nymph., Ithomiinae) before laying eggs: a mechanism to reduce intraspecific competition

Parasites of all kinds affect the behaviour of their hosts, often making them more susceptible to predators. The associated loss in expected future reproductive success of infected hosts will vary among individuals, with younger ones having more lose than older ones. For this reason, young hosts would benefit more by opposing the effects of parasites than old ones. In a laboratory study, the effects of the trematode Telogaster opisthorchis on the anti-predator responses of the upland bully (Gobiomorphus breviceps) and of the common river galaxias (Galaxias vulgaris) were examined in relation to fish age. In a bully population where parasites were very abundant, the magnitude of the fish's anti-predator responses decreased as the number of parasites per fish increased, and this effect was significantly more pronounced in age 2 + and, to a lesser extent, age 3 + fish than in age 1 + fish. In another bully population where parasites were 10 times less abundant, similar effects were noticeable but not significant, whereas no effects of parasites on the responses of galaxiids to predators were apparent. Differences in the abundance of parasites and in their sites of infection in fish may explain the variability among host populations or species. However, in the bully population with high parasite abundance, parasitism has age-dependent effects on responses to predators, providing some support for the prediction that young fish with high expected future reproductive success invest more energy into opposing the effects of parasites than do older fish.     

Effects of angling on population structure of brown trout,Salmo trutta L., in mountain streams of Northern Spain

Effects of angling exploitation on brown trout populations were assessed by comparing fished sections with close ones unfished for at least 20 years, in mountain streams of Asturias (Northern Spain). Both the fish size and age structure significantly differed among sections in the expected direction according to their exploitation status. The main effects were a significant decrease in age structure complexity (diversity), life span, and percent individuals above the legal limit size in the exploited stocks versus the unexploited ones. Trout above the minimum length limit for fishing (18 cm) averaged 19.47% of the fish caught in the unfished sections (sd = 4.01; n = 5), and 4.72% (sd = 3.46; n = 4) in those subjected to angling. Furthermore, fish older than 4 years represented 39.84% (sd = 8.53) and 1.19% (sd = 1.60) of the catch, respectively. Effects on recruitment (density of young fishes) and growth rates (length at age 1 + to 3 +) were not absolutely consistent, though maximum values were associated with fished sections.     

Effects of parasites on larval and juvenile stages of the coral reef fish Pomacentrus moluccensis

The ecological role of parasites in the early life-history stages of coral reef fish is far from clear. Parasitism in larval, recently settled and juvenile stages of a coral reef fish damselfish (Pomacentridae) was therefore investigated by quantifying the ontogenetic change in parasite load and comparing the growth rates of parasitized juvenile fish to those of unparasitized ones. Parasite prevalence in two lunar pulses of Pomacentrus moluccensis was 4 and 0% for larval stage fish, 34 and 56% for recently settled fish and 42 and 49% for juveniles. A significant increase in parasite prevalence with age group was found; the most marked increase occurred immediately after larval fish had settled. Standard length did not model prevalence well; as length is a proxy for age, this indicates that the higher prevalence in recently settled and juvenile fish compared with larvae was not a simple result of parasites accumulating with age. In one of three cohorts, there was some evidence that parasitism affected the growth rate of juveniles, as measured by otolith width. The study suggests that settling on the reef exposes young fish to potentially harmful parasites. This supports the idea that the pelagic phase may have the effect of reducing the exposure of young fish to the debilitating effects of parasites.     

Direct Estimation of Food Consumption of Juvenile Fish in a Shallow Inlet of the Southern Baltic

The species composition and feeding behaviour of fish larvae and juveniles was investigated in a shallow inlet of the Southern Baltic. The aim of the study was to examine if there was a predatory impact of young fish on the observed annual collapse of the copepod population. Dominant fish species were herring (Clupea harengus), perch (Perca fluviatilis) and roach (Rutilus rutilus). Roach larvae preferred shallower areas, whereas young herring and perch were found in open water. Highest consumption values were always observed in the evening. By computing complete evacuation of the digestive tract in approximately 3.5 hours, daily consumption in percent of fish fresh weight was 1.3, 4.7 and 5.5% for young herring, roach and perch, respectively. The impact of young fish on the dynamics of the population of the copepod species Eurytemora affinis is negligible.     

Age‐dependent decline in fin regenerative capacity in the short‐lived fish Nothobranchius furzeri

The potential to regenerate declines with age in a wide range of organisms. A popular model system to study the mechanisms of regeneration is the fin of teleost fish, which has the ability to fully regrow upon amputation. Here, we used the short‐lived killifish Nothobranchius furzeri to analyse the impact of aging on fin regeneration in more detail. We observed that young fish were able to nearly completely (98%) regenerate their amputated caudal fins within 4 weeks, whereas middle‐aged fish reached 78%, old fish 57% and very old fish 46% of their original fin size. The difference in growth rate between young and old fish was already significant at 3 days post amputation (dpa) and increased with time. We therefore hypothesized that early events are crucial for the age‐related differences in regenerative capacity. Indeed, we could observe a higher percentage of proliferating cells in early regenerating fin tissue of young fish compared with aged fish and larger fractions of apoptotic cells in aged fish. Furthermore, young fish showed peak upregulation of several genes involved in fgf and wnt/β‐catenin signalling at an earlier time point than old fish. Our findings suggest that regenerative processes are initiated earlier and that regeneration overall is more efficient in younger fish.     

Theoretical consideration of effect of fishing mortality on growth and reproduction of fish populations

An increase in fish mortality due to fishing can theoretically change the growth and reproduction of fish populations from the viewpoint of adaptation. We address the issue of how an iteroparous fish should convert surplus energy into somatic growth and reproduction at each age under given conditions of mortality. A model of life history, which maximizes the net reproductive rate using the discrete maximum principle, is improved employing a new relationship between body weight and surplus energy which we have recently proposed. The model is applied to the North Sea plaice Pleuronectes platessa, for which it has been reported that the average length of young fish had increased whereas that of old ones had decreased for some decades. Although the model cannot directly explain the former phenomenon, the two phenomena can be interpreted as a change in the optimal life history due mainly to an increase in mortality.     

Age specific food utilization and spatial distribution of the puffer,Takifugu niphobles, over an intertidal sand flat

Synopsis Spatial distribution and feeding habits of the puffer fish,Takifugu niphobles, were studied to understand its mode of resource utilization in an intertidal sand flat at Tomioka in the western coast of Kyushu Island, Japan. The transect survey during high tides showed the presence of young puffers near the shoreline, while adults were mainly found in the offshore area of the sand flat. The gut contents analysis showed that although the young puffers foraged more frequently on organisms dwelling in the inshore area than the adults, both puffers fed mainly on the ghost shrimpCallianassa japonica inhabiting the entire sand flat. There was no apparent difference in the size of consumedC. japonica between the young and adult puffers. However, comparison of size structures of ghost shrimps in the field and in the gut contents showed that the young puffers foraged both from inshore and offshore areas of the sand flat, while the adults foraged mainly in the offshore area. This suggests that young puffers move more frequently over the sand flat with tides than adult ones. This pattern of trophic separation among size classes may reflect environmental features of the intertidal sand flat with large tidal fluctuations.     

Aspects of the biology of the catfish Clarias lazera (Cuv. & Val.) related to its economic cultivation

The seasonal abundance, population structure, reproduction, feeding, respiratory adaptations and tolerance were studied in the catfish Clarias lazera (Cuv. & Val.) in the reservoir of Jebel Aulia on the White Nile, and in the Green-Belt canals near Khartoum. Continuous monitoring of the ripe, spent and spawning females and immature fish in the population revealed that C. lazera breed synchronously in the autumn in the reservoir and rather sporadically in the canals. Medium-sized females were more fecund than old and young females. Administration of pituitary extract enhanced maturation, induced spawning in mature fish, stimulated body growth, especially in maturing specimens, and produced, as a side-effect, a diuretic response. Mature fish depended on pulmonary respiration for about 45% of the total oxygen requirement. C. lazera fed preferentially on its fry and on decayed proteinaceous food. The suitability of this species for economic cultivation is discussed.     

The trophic interactions of young Arctic grayling (Thymallus arcticus) in an Arctic tundra stream

1. Young (0+) Arctic grayling (Thymallus arcticus) have the potential to control the trophic structure of Arctic tundra streams through consumption, nutrient excretion and the modification of prey behaviour. The effect of young grayling on three trophic levels (algae, invertebrates and fish) was investigated by manipulating fish density and by fertilizing the river with phosphorus (P). 2. Nutrients, epilithic chlorophyll a, benthic invertebrates and fish biomass were measured within each fish density treatment (0, 4, and 40 fish m^–2) within the P-limited reference zone and the P-enriched fertilized zone of the Kuparuk River, Alaska. 3. Epilithic chlorophyll a increased with increased fish density in both reference and fertilized zones, while mayfly density decreased with increased fish density in the fertilized zone only. Final mean mass of young grayling in the 40 fish m^–2 cages was lower than mean mass in the 4 fish m^–2 cages. 4. Young grayling may produce a top-down cascading trophic effect in areas where nutrients are not limited. 5. River nutrient status and river discharge may modify the strength of top-down control by young grayling.     

Fish-zooplankton interactions and their effects on water quality of a tropical Brazilian reservoir

The influence of zooplanktivorous fishes on the plankton community and water quality of Americana Reservoir, Brazil was studied experimentally in 4 floating enclosures during the dry seasons (July–September) of 1982 and 1983. Two enclosures were stocked with adult fish (Astyanax bimaculatus in 1982;A. fasciatus in 1983) at near maximal densities measured in the reservoir upper surface waters (35 m^–2) and two were fish-free during each experiment lasting about one month. Marked differences were evident between the fish and fish-free enclosures after a 2–3 week period in each experiment, particularly with respect to water transparency, phytoplankton biomass, and zooplankton abundance as well as species and size composition. By the end of each experiment water transparencies were lower and phytoplankton biomass higher in the fish enclosures compared to those without fish. Also at that time Rotifera were the prominent zooplankters in the fish enclosures and Cladocera in the fish-free ones. Larger or more conspicuous species of Cladocera asDaphnia gessneri, D. ambigua, andMoina micrura were present in the fish-free enclosures but not in the fish enclosures. The interactions between fish predation, zooplankton grazing, phytoplankton biomass and water quality conditions are discussed in relation to eutrophication of a tropical aquatic ecosystem.     

Impact of micropredatory gnathiid isopods on young coral reef fishes

The ecological role of parasites in the early life-history stages of coral reef fish, and whether this varies between fish with and without a pelagic phase, was investigated. The susceptibility to, and effect of reef-based micropredatory gnathiid isopods on larval, recently settled, and juvenile fishes was tested using two damselfishes (Pomacentridae): Neopomacentrus azysron, which has pelagic larvae, and Acanthochromis polyacanthus, which does not. When larval and recently settled stages of N. azysron and very young A. polyacanthus juveniles (smaller than larval N. azysron) were exposed to one or three gnathiids, the proportion of infections did not vary significantly among the three host types or between the number of gnathiids to which the fish were exposed. The overall infection was 35%. Mortality, however, differed among the three gnathiid-exposed host types with most deaths occurring in larval N. azysron; no mortalities occurred for recently settled N. azysron exposed to one or three gnathiids, and A. polyacanthus exposed to one gnathiid. Mortality did not differ significantly between larval N. azysron and A. polyacanthus juveniles, failing to provide support for the hypothesis that reef-based A. polyacanthus juveniles are better adapted to gnathiid attack than fish with a pelagic phase. The study suggests that settling on the reef exposes young fish to potentially deadly micropredators. This supports the idea that the pelagic phase may allow young fish to avoid reef-based parasites.     

Fish recruitment in a large,temperate floodplain: the importance of annual flooding,temperature and habitat complexity

1. Large river floodplains are considered key nursery habitats for many species of riverine fish. The lower Volga River floodplains (Russian Federation) are still relatively undisturbed, serving as a suitable model for studying the influence of flooding and temperature on fish recruitment in floodplain rivers. 2. We examined the interannual variability in recruitment success of young‐of‐the‐year (YOY) fish in the lower Volga floodplain in relation to flood pulse characteristics and rising water temperatures in the spring. We sampled four areas with different flooding regimes, in three consecutive years (2006–2008). 3. Extensive areas with a long duration of flooding accommodated high densities of young fish. This suggests that extended inundation improves the recruitment success of river fish. In areas with extensive flooding, the biomass of YOY of most fish species was about three times higher in 2006 and 2007 than in 2008. We hypothesise that low spring temperatures in 2008 may have caused this reduced recruitment and that a flood synchronised with rising temperature enhances recruitment success. 4. Extensive flooding was particularly favourable for species characterised by large body size, delayed maturation, high fecundity and low parental investment, such as pike Esox lucius, roach Rutilus rutilus and ide Leuciscus idus. Gibel carp Carassius gibelio, a species tolerant of high temperature and hypoxia, did particularly well in small waterbodies in the driest parts of the floodplain. 5. Structural characteristics of floodplain waterbodies explained much of YOY fish density. These species–environment associations varied from year to year, but some species such as common bream Abramis brama, roach and gibel carp showed consistent relationships with structural habitat characteristics in all years, despite large interannual fluctuations in flood pulse and spring temperature.     

CHANGES IN THE ABUNDANCE AND MORTALITY RATE OF TIGERFISH IN THE EASTERN BASIN OF LAKE KARIBA

SUMMARY

Tigerfish populations increased in the eastern basin of Lake Kariba following the successful invasion of the pelagic clupeid Limmothrissa miodon. Strong year-classes persisted for several years but the number of young tigerfish declined, a phenomenon which cannot be accounted for. The influence of these year classes on different fisheries was demonstrated. The mortality rate of the younger fish was related to the rate at which their numbers were changing with mortality rates being highest when numbers were declining most rapidly. Concern about the future of this fish was expressed because of increased fishing in its main breeding area.     

Biology of Clupeichthys aesarnensis (Clupeidae) in Ubolratana Reservoir,Thailand, with Special Reference to Food and Feeding Habits

The freshwater sardine Clupeichthys aesarnensis is a zooplanktivore like many clupeids. In Ubolratana reservoir, Thailand, it feeds selectively on larger zooplankters, especially Cladocera and to a lesser extent on Copepoda. Other zooplankters are also consumed together with both living and dead insects and occasionally its own young. It feeds during the day. Our results indicate that the slight seasonal differences in food consumed probably reflects differences in availability at different seasons and sites. The fish grows in weight, as expected, at a higher rate than the cube of its length. The condition factor is the same for males and females and shows some seasonal variation. Data on fecundity and gonadosomatic index mark this fish as highly fecund and a year-round spawner. Its short life span, favourable growth and high fecundity make it a valuable source of cheap protein. In 1990, 17% (about 300 tons) of the fish catch from Ubolratana came from this fish.     

Susceptibility to freshwater acidification by two species of loon: Red-throated Loon (Gavia stellata) and Arctic Loon (Gavia arctica) in southwest Sweden

In southwest Sweden, the two species of loon, Gavia stellata and G. arctica, have shown different trends in population size and production of young during the last decades. Both species fish in oligotrophic freshwaters, susceptible to acidification. The number of breeding sites occupied by G. stellata has been reduced by almost 50% during the last 40–50 years. For G. arctica, there are no indications of significant declines in population size or reproductive success during the last 20 years. The different trends in numbers and production of young might reflect different susceptibility to the ecological changes in acidified lakes. G. stellata prefer fishing lakes with high abundance of Acerina cernua and salmonid and cyprinid fish, such as Coregonus albula and Rutilus rutilus. They also feed their prefledged chicks almost entirely on cyprinid and salmonid fish. G. arctica prefer fishing lakes with high transparency and, when feeding in groups, high abundance of Perca fluviatilis. Their young can be fed on aquatic insects as a supplement to the fish diet. Thus, G. stellata to a higher degree than G. arctica relies on fish which are susceptible to low pH, and G. arctica may also benefit from the increased abundance of aquatic insects in lakes with reduced predation from fish. Furthermore, high water transparency is important for the selection of lakes by G. arctica but not by G. stellata. In G. stellata, high contents of mercury in eggs can be related to the intake of fish in lakes affected by acidification.     

Mancae of the parasitic cymothoid isopod, <Emphasis Type="Italic">Anilocra apogonae</Emphasis>: early life history,host-specificity,and effect on growth and survival of preferred young cardinal fishes

Juvenile parasitic cymothoid isopods (mancae) can injure or kill fishes, yet few studies have investigated their biology. While the definitive host of the adult cymothoids is usually a single host from a particular fish species, mancae may use so-called optional intermediate hosts before settling on the definitive host. Little, however, is known about these early interactions. The cymothoid isopod, Anilocra apogonae, infests the definitive host, Cheilodipterus quinquelineatus. This study examined their host preference among potential optional intermediate hosts. Their effect on the growth and mortality of the young of three apogonid fishes, including the definitive host, was investigated. The number of mancae produced per brood was positively correlated with female length. When given a choice of intermediate hosts, significantly more mancae attached to Apogon trimaculatus (Apogonidae) than to Apogon nigrofasciatus. When presented with Ap. trimaculatus and Pomacentrus amboinensis (Pomacentridae), mancae only attached to Ap. trimaculatus suggesting that mancae may show a taxonomic affiliation with preferred hosts. Mancae fed on all three apogonid species, with C. quinquelineatus being fed on earlier than Ap. trimaculatus and Ap. nigrofasciatus. Mancae feeding frequency, adjusted for fish survival, was lowest on C. quinquelineatus and highest on Ap. trimaculatus. Infested apogonids had reduced growth and increased mortality compared with uninfested fish. A. apogonae mancae can use several species of young apogonid fishes as optional intermediate hosts. Via reduced growth and increased mortality, mancae have the potential to negatively influence definitive host populations and also other young species of apogonid fishes.     

Anti-Predator behaviour of naïve compared experienced juvenile roach

Juvenile roach Rutilus rutilus without any previous contact with predatory fishes reacted to the presence of alarm substances more intensively than fish with previous experience. Among several types of behavioural response observed, some, such as hiding, were not registered in experienced fish. The most pronounced difference between the two juvenile fish categories was manifested in feeding. Naïve fish used more time for feeding than experienced ones. The experiment showed that alarm substance originating from small and young and medium roach induced a stronger reaction than the substance extracted from large and oldéê fish.     

Changes in fish species composition in Lake Naivasha,Kenya

The fish species composition in Lake Naivasha has been modified during recent years. Out of seven introduced and one indigenous species reported in 1962, only three introduced ones are found today. The elimination of species has been brought about by predation and changing ecological conditions. The most common fish species today is Sarotherodon leucosticuus. The hybridization found by previous workers between S. leucostictus x S. spilurus niger has stopped, as S. s. niger is no longer found in the lake. Most of the hybrid characters have been lost by the few surviving hybrids due to backcrossing between hybrids and between hybrids and S. leucostictus. The hybrids now mostly resemble S. leucostictus.     

Chafing in fishes: occurrence,ontogeny, function and evolution

Synopsis Modal action patterns used in maintenance behavior have often been included in animals' communication repertoires during evolution, yet for fish neither the occurrence nor subsequent ritualization of maintenance behavior has been demonstrated. We review the literature and show that one maintenance behavior, the chafe, occurs in at least 30 families of fish. The chafe thus appears to offer a fruitful tool for the phylogenetic analysis of behavior of fish. We show that chafing in Etroplus maculatus and Xiphophorus helleri functions to remove sources of irritation from their skin. We also show that during ontogeny and when in social groups the frequency of chafing does not change with age in E. maculatus and E. suratensis. Etroplus suratensis have about twice the body surface and chafe twice as often as E. maculatus. Chafe-like behavior in Etroplus is observed during ontogeny when young glance on their parents' body. Young E. maculatus without parents present chafe more frequently than young with parents present suggesting that chafing on the substrate may substitute for parent contacting. Chafing is also included in adult behavior where it occurs during pair-formation, nest relief behavior and as an interspecific signal performed by the cleaner E. maculatus upon the host E. suratensis. The maintenance chafe and glance upon the parent both occur rapidly while the chafe performed during pair-formation is slow suggesting a degree of ritualization.     

Predator detection and avoidance by lotic mayfly nymphs of different size

We studied antipredatory responses of lotic mayfly (Baetis) nymphs in a factorial experiment with four levels of fish presence: (1) a freely foraging fish (the European minnow,Phoxinus phoxinus), (2) a constrained fish, (3) water from a fish stream, (4) water from a fishless stream. LargeBaetis nymphs drifted mainly during night-time in treatments involving either the chemical or actual presence of fish, whereas no diel periodicity was observed when the water was not conditioned with fish odour. The response was strongest when the fish was uncaged, which suggests that visual or hydrodynamic cues are needed in addition to chemical ones for an accurate assessment of predation risk. Fish presence had no effect on the drift rates of small nymphs. Instead, they increased their refuge use in the presence of a live fish. Chemical cues alone did not have any effect on the refuge use of any of theBaetis size classes. Our results indicate active drift entry by mayfly nymphs. Because predation pressure is spatially and temporally variable, nymphs must sample the environment in order to locate predator-free areas or areas with low predation risk. Drifting should be the most energy-saving way to do this. To avoid the risk from visually feeding fish, large individuals can sample safely (i.e. enter drift) only at night-time, while the small ones can also do this safely during the day. We suggest that, contrary to some earlier assumptions, mayfly drift is not a fixed prey response. Instead,Baetis nymphs are able to assess the prevailing predation pressure, and they adjust their foraging behaviour accordingly.