Intertidal territoriality and time-budget of the surgeonfish, Acanthurus lineatus, in American Samoa

Synopsis The herbivorous surgeonfish Acanthurus lineatus aggressively maintained feeding territories in the surf zone of the outer reef flat in American Samoa. Intertidal territories were re-established each morning, as well as after displacement by low tides or rough surf. Day-to-day site fidelity of recognizable individuals was high: 99.9% return rate per day for adults (15–20 cm), 99.6% for juveniles (8–13 cm), and 97.2% for recruits (2.5–5 cm). Fish fed on turf algae primarily in the afternoon (80% of available time), and spent 10% of their time on active territorial defense and 2–13% of their time on forays from their territory. On average, a fish defended its territory 1900 times daily and took 17 000 bites (= 7400 bites m^–2 d^–1), but rough surf reduced feeding by 60% and defense by 75%. High territorial defense requirements significantly reduced feeding rates. Although the distribution and behavior of this species in Samoa was in large part similar to that reported for it elsewhere (Australia, Indian Ocean), there were notable differences: in Samoa A. lineatus densities within colonies were greater (0.4 fish m^–2), territory size was smaller (2.3 m²), and defense rate against intruders was greater (2.5 attacks min^–1). These differences in Samoa may be related to their smaller body size, greater abundance or increased food supply caused by hurricane damage to reefs which has enhanced the algal turfs that A. lineatus feeds upon.     

Depth-related differences in territory size and defense in the herbivorous cichlid,neolamprologus moorii, in lake tanganyika

Neolamprologus moorii, a small herbivorous cichlid of Lake Tanganyika, defends its territory against food competitors. Territory size and territorial defense were compared between two sites at different depths. In the shallow site, more fishes intruded into the territories than in the deep site, owing to the higher density fish population in the former. The territory holders in the shallow site attacked intruders more often, although the ratio of attacks to number of intruders was similar to that of the deep site. The territories in the deep site were larger and contained a greater amount of algae than the shallow site. The larger territory size in the deep site may have resulted from the lower cost of territory defense due to the lower competitor density and from the need to maintain a greater amount of food resources to compensate for lower algal productivity.     

Ontogenetic variations in the type and size of prey consumed by juvenile coho,Oncorhynchus kisutch,and chinook,O. tshawytscha,salmon

Synopsis Stomach contents of juvenile coho,Oncorhynchus kisutch, and chinook,O. tshawytscha, salmon collected in purse seines off the coast of Washington and Oregon were examined for variations related to predator size. There was a general trend toward increasing consumption of fish with increasing body size, due mainly to the increase in northern anchovy biomass consumed by the larger salmon. Most of the major prey taxa showed significant differences among the size classes examined for both salmon species. There was a direct relationship between predator and prey size for both coho and chinook, but considerable variation was found in prey length consumed within each size class. Prey width did not provide as good a fit as prey length for either species. In general, coho consumed larger fish prey in relation to their body length than chinook but there were substantial differences by month or year of collection.     

Shoal Choice in the Banded Killifish (Fundulus diaphanus,Teleostei, Cyprinodontidae): Effects of Predation Risk,Fish Size,Species Composition and Size of Shoals

Banded killifish (Fundulus diaphanus) were presented individually with a choice of shoaling with either of two stimulus shoals which differed in shoal size, species composition, and fish body size, before and after a simulated avian predator attack. When threatened, test fish preferred to shoal with the larger of two conspecific shoals, but only if members of both stimulus shoals were of the same size class as the test fish. Otherwise, they preferred to shoal with similarly sized fish irrespective of shoal size; threat of predation increased the magnitude of this preference. Furthermore, test fish preferred a shoal of similarly sized shiners (Notemigonus crysoleucas) over larger killifish, when shoal sizes were identical. This indicates that body size plays a key role in shoal choice, overriding the effects of shoal size and species preference. Notwithstanding the above, shoal choice was affected by predator threat only when differences between shoal size or body size of stimulus fish were large.     

Influence of brood size and offspring size on parental investment in a biparental cichlid fish,Neolamprologus moorii

Both males and females ofNeolamprologus moorii, a substrate-spawning cichlid fish in Lake Tanganyika, tend their eggs and fry. In this study, the influence of brood size and fry size on parental investment of this species was examined under natural conditions. Breeding parents intensively attacked fry-eating fishes that approached their broods. The attack rate by the parents against the approaching fry-eaters was positively correlated with brood size and negatively with fry size, but was much more strongly related to brood size. This suggests that the parental decision for brood defense appeared to be primarily determined by brood size. The reason for fry size being less important in the parental decision may be that even large fry have a low survival ability on their own under the high predation pressure in the study sites.     

Differences in Aggressiveness in the Midas Cichlid Fish (Cichlasoma citrinellum) in Relation to Sex,Reproductive State and the Individual

The Midas cichlid, Cichlasoma citrinellum, is monogamous and biparental. Because of competition for limited spawning sites and intense predation on their young, vigorous defense of their territory is essential. Although both sexes engage in defense, they differ in aggressiveness. The aggressive responses of both sexes were measured by counting the number of bites and bumps each fish directed toward its own mirror image. The size of the fish's genital papilla was also recorded to estimate its reproductive state. Compared with females, males had higher median mirror scores with greater variance. The scores of individual males were also more consistent through time than were those of females. Females close to spawning had the highest mirror scores, whereas male scores were highest early in the reproductive cycle. Selection has apparently favored aggressiveness in both sexes. We argue, however, that differences in aggression are the result of selection acting dissimilarly on the two sexes.     

Diet and intestinal helminths in a population of perch, Perca flavescens

In 1967 and 1968 1310 Perca flavescens (Mitchill) were examined from Lake Opeongo, Ontario for changes in five diet categories and in incidence of eight intestinal helminths in relation to seasons, host size and sex. Male fish were less common than females and were smaller. A high proportion of fish (57.7 %) had empty stomachs, but of the four types of foods taken microcrustacea were high in spring, late summer and again in early winter; insects increased in summer with another peak in autumn; crayfish had a small peak in spring and a larger one in autumn; and fish were lowest in summer. Males ate more smaller foods (microcrustacea) than females, but females ate more larger foods (crayfish and fish); no sex difference was seen with regard to insects or empty stomachs. Male fish ate very few larger items, but females showed an increase in food size with increasing size of fish. There was no seasonality in incidence of fish free of all parasites, but two trematodes Bunodera sacculata Van Cleave & Mueller and B. luciopercae (Müller), and one cestode Proteocephalus pearsei La Rue showed seasonality with populations lowest in fish in summer; and one trematode Crepidostomum cooperi Hopkins and one nematode Dacnitoides cotylophora Ward & Magath showed seasonality with populations highest in summer. In addition one cestode Bothriocephalus sp., one nematode Spinitectus gracilis Ward & Magath and one acanthocephalan Leptorhynchoides thecatus (Linton) showed no seasonality, perhaps on account of the low incidence in the case of Bothriocephalus sp. and L. thecatus. No parasites were more common in males, but two (P. pearsei and L. thecatus) were more common in females. In both males and females, with increasing size fish, (i) fish free of all parasites decreased, but (ii) incidence of C. cooperi increased. Incidence of B. luciopercae, Bothriocephalus sp., S. gracilis and L. thecatus all increased with increasing size of fish only in females. The relationship between diet and incidence of intestinal helminths is discussed in the light of what is known of their life cycles. The exercise illustrates our ignorance of population ecology of fish parasites and the interactions of parasites and their host populations.     

Overwinter body condition,mortality and parasite infection in two size classes of 0+ year juvenile European bitterling Rhodeus amarus

Body condition and parasite abundance were examined in two size classes of European bitterling Rhodeus amarus during the first overwintering period in two seasons (2007–2008 and 2009–2010). Body condition of large fish did not change during winter, and increased significantly in March. From November to February, small fish showed a decreasing trend in condition. Despite a significant increase in March condition of small fish only reached the same level as before winter. Total parasite abundance increased significantly in winter in both fish size classes, reflecting a seasonal increase in monogenean infection. Large fish were parasitized significantly more than small fish during winter, but only in small fish was a negative correlation between parasite infection and condition found and a significant decrease in parasite abundance recorded after wintering, indicating mortality of heavily infected individuals with low condition during the winter. A trend for higher overwinter mortality in small fish was found under semi‐experimental conditions. The decrease in condition during the winter period in small fish may reflect faster energy depletion generally expected in smaller individuals. The results indicate that parasite infection may contribute to the overwinter mortality of 0+ year R. amarus, with a stronger effect in smaller individuals.     

Chaoborus and fish-mediated influences on Daphnia longispina population structure,dynamics and life history strategies

Summary This study examined the long term effects of predation by larvae of the midge Chaoborus and simulated fish predation on experimental Daphnia longispina populations. Chaoborus predation, relative to fish predation, led to populations composed of larger individuals as a whole, larger egg-bearing individuals, and a larger primiparous instar. Daphnia retained helmets beyond the first instar in response to the presence of Chaoborus. Both types of predation, relative to predator-free controls, reduced prey population size and rates of increase, but increased population death rates. The reduction in population size due to predation led to increased resource availability for individuals remaining in the populations and increased individual fecundity in the predation treatments. The differences noted between the Chaoborus, fish, and control treatments increased with predation intensity.     

The relations between 0+ fish density,zooplankton size and the vulnerability of pikeperch,Stizostedion lucioperca,to angling in the Frisian lakes

During a five year study, the size and abundance of zooplankton and 0+ fish in September were registered in a number of Frisian lakes. The mean size of Daphnia was related to the abundance of planktivorous 0+ fish in September. Immigration of fish larvae into the Frisian Lake District from the IJsselmeer in June was observed in 1979 and 1980. The abundance of 0+ fish was negatively related and the size of Daphnia was positively related to the vulnerability to angling of predatory pikeperch.     

Predation of freshwater jellyfish on Bosmina : the consequences for population dynamics,body size,and morphology

Invertebrate predators may cause strong changes in behaviour, life-history, and morphology of prey species. However, little is known about the influence of jellyfish on such characteristics of their prey. This study analyses the impacts of the freshwater jellyfish Craspedacusta sowerbii on life history and morphological defenses in a population of the cladoceran Bosmina longirostris . Length of mucro and antennule, size-dependent number of eggs, size at maturity, and size of juveniles, adults, and egg-carrying females were investigated during a 23 days experiment using medusae-enriched and control enclosures filled with natural plankton populations. Significant differences in parameters investigated were found not only between treatments, but also within treatments over time. Changes in Bosmina life-history parameters and morphology in controls were probably due to predation by cyclopoid copepods. The significant increase in the size of adults and egg-carrying females as well as the increase in mucro and antennule length in medusae-enriched enclosures are discussed as defense strategies against the freshwater jellyfish.     

Home range,movements, and density of the central stoneroller,Campostoma anomalum,in a small Ohio stream

Synopsis A population of central stonerollers, Campostoma anomalum, in Harker's Run, Butler County, Ohio U.S.A., was examined during autumn, 1980, to determine the species' movements, density, and home range size. During the study period, 170 fish were marked by fin clips and released into the specific pool or riffle where they were captured within the 187 m study section. Eighty percent of the recaptured, marked fish (20) were recaptured in their initial capture area (specific pool or riffle). No fish moved more than 135 m from its original capture area. Density estimates of C. anomalum for each pool and riffle within the study section ranged from 0.10–3.91 fish m⁻² (mean = 1.25 fish m⁻²). Home range size was estimated to be 35.2 ± 14.1 m (mean ± 95% CI) of stream length. Campostoma anomalum in Harker's Run occurred at densities similar to those reported for the species in other streams, and their home ranges in this system were of similar size to those of other small, stream-dwelling fishes.     

Imaging scale surface topography of an endemic cyprinid fish,Garra sharq from the Arabian Peninsula: An integrated optical light and scanning electron microscopy approach

The optical light microscopy and scanning electron microscopy techniques have proven to play a key and noteworthy role in the advancement of morphological studies in general, and in investigating fish scale morphology in particular. These techniques have illustrated several hidden architectural structures in scales that contribute effectively to fish identification and classification. The scale morphological and topological characters such as type, size, shape, lateral surface, focus position, circuli appearance, radii type, lepidonts, and posterior and anterior margin shapes were obtained using macro- and microscopic analysis in six body regions for three size classes of Garra sharq, a cyprinid endemic fish of the Arabian Peninsula. The general scale type in the studied G. sharq species was a basal elasmoid cycloid and a sectioned type. As a protective structure, the scales display several specific characteristics including firm attachment to the fish body, overlapping, and thin structure with a high surface area and high strength. These characteristics improve scale resistance to penetration, increase protection against mechanical injury and microbial infection, enhance scale flexibility, reduce fish weight (reduce friction drag), and increase scale transparency. The scales demonstrate plasticity in focus shape, size, and position in the six fish body parts and fish size groups. The examined scales displayed narrow or wide grooves (radii) in three types including primary, secondary, and tertiary present in all four scale fields (anterior, posterior, and laterals), thus a tetra-sectioned type that is almost specific to the genus Garra. This characteristic also increases scale flexibility. The rostral margin of scales was characterized by the presence of waved and striate types. The lepidont shape and size varied being blunt, flat, pointed, tiny, sharp, short, and long. Some of these scale characters and their morphologies could be used as an alternative tool for identification, classification, and phylogenetic interpretation among the different freshwater fish species and genera.     

An energy-based analysis of particulate-feeding and filter-feeding by blue tilapia,Tilapia aurea

Synopsis Adult blue tilapia, Tilapia aurea, employ filter-feeding as their primary feeding method, but feed as visual, particulate-feeding zooplanktivores as juveniles. We used measurements of oxygen utilization in enclosed chambers to assess filter-feeding energy costs, and videotaped observations of particulate-feeding to compute energy costs for this behavior. Weight-specific costs of filter-feeding are highest for smaller individuals, and decrease exponentially with fish size. Particulate-feeding costs increase with fish size and with distance travelled during attacks on zooplankton prey. These data were used in combination with published information to examine the energetics of the switch in feeding behavior in relation to the profitability of each feeding method. We develop a model which can be used to predict feeding behavior in relation to fish size and plankton array.     

Agonistic behaviour and control of access to hiding places in two intertidal blennies, Lipophrys pholis and Coryphoblennius galerita (Pisces: Blenniidae)

In this study we investigated the relationships between dominance rank and access to shelters in captive groups of Lipophrys pholis and Coryphoblennius galerita, as well as the effects of group size and shelter availability. Dominance rank was strongly correlated with size in juvenile L. pholis and with sex and size in adult C. galerita, males being dominant over females of similar size. Access to shelters was significantly correlated with dominance rank. For both species, most interactions occurred out of shelters. Direct disputes over shelters were always initiated by the dominant fish and the initiator was always the winner. The rate of aggression per fish per unit time decreased with an increase in the number of fish in L. pholis but not in C. galerita. No significant differences were found in groups differing in the number of shelters. C. galerita showed a higher rate of agonistic interactions and a higher proportion of overt aggression than L. pholis. It is suggested that one of the functions of agonistic interactions in these fishes is the control of a set of shelters, in the network of pathways used by each individual within its home range, minimising the time required to hide in case of danger. Received in revised form: 29 January 2001 Electronic Publication     

Ontogenetic diet shifts of bull-rout, Myoxocephalus scorpius (L.), in the south-western Baltic Sea

The stomach contents of 533 bull‐rout, Myoxocephalus scorpius (L.), were collected during February–March and October–November 1997 in the south‐western Baltic Sea in order to study the feeding ecology and investigate diet changes between seasons and with the increasing size of the fish. The isopod Mesidotea entomon, and herring Clupea harengus, were the dominant species in the diet, accounting for 99% in weight of all bull‐rout sampled in spring and autumn. Mysis mixta was frequent but less important in weight; analysis of the ontogenetic diet shift showed the presence of M. mixta essentially in the smaller size‐classes. Herring was eaten almost exclusively by individuals larger than 21 cm total length; its importance increased with increasing size of bull‐rout. The isopod M. entomon was abundant in all size‐classes examined. Prey‐size and the size of the principal prey, M. entomon, showed a significant increase with increasing bull‐rout size. The diet shift from mysids to fish was followed by a change in the weight‐length relationship. Cluster analysis confirmed two distinct size groups of >26 cm and <24 cm. In conclusion, the data indicate that the diet of bull‐rout partially overlaps with that of herring in the first trophic stage, and with that of cod in the second part of the bull‐rout life cycle.     

A New Blind Cave Fish Population of Genus Astyanax: Geography, Morphology and Behavior

A new population of blind, cave dwelling tetra fish of the genus Astyanax was discovered in Granadas Cave, in the Balsas drainage, southern México. All blind Mexican tetras previously described are from Tampico and San Luis Potosí, northern México. The discovery of a new blind morph thus represents an independent colonization and convergent adaptation to the cave environment by this fish. Individuals of this population display variability of their troglomorphic features. Some individuals presented asymmetrical degeneration of the eyes, where one was normal, but the other somewhat reduced in size and complexity. Loss of pigmentation and eye reduction, although sometimes correlated, were not always linked; reduced eyes were found on pigmented fish and unpigmented fish often possessed normal eyes. Some individuals had reduced lens size or an absence of lens altogether. Retina is highly modified with photoreceptors sometimes absent. Eye reduction was correlated with a diminished size of the optic lobes and an increase of the prosencephalon. Modifications of the skull involve closing in of the circumorbital series of bones. Certain aspects of behavior are also modified.     

Factors affecting feeding selectivity of visual predators on the copepod Acartia tonsa: locomotion,visibility and escape responses

Visual predation by fish on copepods involves prey encounter, attack and capture; during any of these processes prey selection can occur. Developmental changes in copepods, including increases in swimming speed, size and image contrast increase the encounter rate and distance at which they can be detected by predators. Copepods compensate for this increase vulnerability with age through diel vertical migration and improved escape capabilities. This study quantifies the changes in swimming speed and movement pattern with developmental stage of the copepod Acartia tonsa, using a video-computer system for motion analysis. Changes in visible size and image contrast with developmental stage were quantified under simulated natural illumination conditions using a video based image analysis system. The escape responses of the naupliar stages of the copepod Acartia tonsa were quantified in response to a stationary pipette sucking in water at a constant speed. Accurate quantification of the parameters that affect feeding selectivity of planktivorous fish will provide the basis for evaluation of their relative importance in future studies.     

Cladoceran community responses to biomanipulation and re‐oligotrophication in Lake Vesijärvi,Finland, as inferred from remains in annually laminated sediment

1. We studied the role of zooplankton in biomanipulation and the subsequent recovery phase in the Enonselkä basin of Lake Vesijärvi, using subfossil cladocerans in annually laminated sediment. Measures to restore the Enonselkä basin included reduction in external nutrient loading and mass removal of plankti‐ and benthivorous fish. Water clarity increased and the lake changed from a eutrophic to a mesotrophic state. However, some signs of increased turbidity were observed after 5–10 years of successful recovery. 2. Annual laminae in a freeze core sample were identified and sliced, based on the seasonal succession of diatoms. Cladoceran remains and rotifer eggs were counted, and Daphnia ephippia and Eubosmina and Bosmina ephippia and carapaces were measured. Annual changes in pelagic species composition were studied with principal component analysis. Individual species abundance, size measurements and various cladoceran‐based indices or ratios (commonly used to reconstruct changes in trophic state and fish predation) were tested for change between four distinct periods: I (1985–1988) dense fish stocks, poor water quality; II (1989–1992) fish removal; III (1993–1997) low fish density, improved water quality; IV (1998–2002) slightly increased fish density and poorer water quality. 3. After the removal of fish, the mean size of Daphnia ephippia and Eubosmina crassicornis ephippia and carapaces increased significantly. In contrast, the percentage of Daphnia did not increase. When based on ephippia, the ratio Daphnia/(Daphnia + E. crassicornis) increased, but the interpretation was obscured by the tolerance of fish predation by small Daphnia and by the fact that bosminids were the preferred food of roach. Moreover, ephippial production by E. crassicornis decreased in recent years. 4. The abundance of Diaphanosoma brachyurum and Limnosida frontosa increased significantly after the fish population was reduced, while that of Ceriodaphnia and rotifers decreased. 5. The expanding littoral vegetation along with improved water clarity was clearly reflected in the concentration of littoral species in the deep sediment core. The species diversity index for the entire subfossil community also increased. 6. The period of faltering recovery was characterised by greater interannual variability and an increased percentage of rotifers. Nevertheless, the mean sizes of Daphnia ephippia and E. crassicornis ephippia and carapaces indicated a low density of fish. The deteriorating water quality was apparently related to multiple stressors in the catchment after rehabilitation, such as intensified lakeshore building, as well as to exceptional weather conditions, challenging the management methods in use.     

Size‐based interactions and trophic transfer efficiency are modified by fish predation and cyanobacteria blooms in Lake Mývatn,Iceland

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