Behavioral differences of various ecological groups of roach Rutilus rutilus and perch Perca fluviatilis

The intrapopulation morphological and behavioral polymorphism of roach (Rutilus rutilus) and perch Perca fluviatilis) was studied. It was shown that marker indices for distinguishing intrapopulation groups are the size of the mouth opening and the index of the body shape in roach and the coefficient of pigmentation in perch. Based on analysis of the data of indices, it was found that there are two ecological groups—coastal and pelagic in populations of roach and perch. Several behavioral differences in individuals of various ecological groups were revealed. Comparison of the defense reaction of perch individuals belonging to various ecological groups was performed. The assessment of the effects of hydrodynamic activity on the survival of perch individuals belonging to various ecological groups was made. Differences in the swimming capacity of juvenile roach developing under conditions of biotopes of various types were established. Suggestions were made on the mechanisms of formation of intrapopulation groups of roach and river perch.     

Zur Ökologie der Acoela (Turbellaria) in der Deutschen Bucht

Ecological investigations on the turbellarian order Acoela were carried out from 1962 to 1965 in List (Sylt), Helgoland, Wilhelmshaven and Juist. The sediments in the eulittoral of the Frisian Islands (Juist) and the Jade are structurally rather similar; sediment mobility or muddy components prevent establishment of an interstitial fauna. Helgoland possesses a great variety of different biotopes; this island harbors the highest number of species in the southern North Sea. In contrast to Juist, Sylt offers predominantly sandy biotopes; in addition to the mudliving species of the epifauna, a number of typical interstitial species was recorded. Of 82 species of Turbellaria Acoela identified, only 1 lives in greater sediment depths; all others are confined to the uppermost centimeters or millimeters of the sediment. Besides the sediment boundaries, the low water line forms an important population barrier. The differences in the sediments can be related to specific morphological and habitual adaptations of their inhabitants. Acoela living in interstitial spaces possess mostly a long and slender body form, which, in turn is correlated to internal organization. Most Acoela species which exist in the spaces between sand grains have an unpaired ovary, shifted from near the statocyst to the area behind the mouth opening. Big vacuoles in the peripheral parenchym counteract mechanical deformation by the sediment. Fixation mechanisms occur in form of tail plates, adhesive glands or caudal organs. The body of mud-living Acoela is usually short and stout. Special structural adaptations are absent. The determining factors in the colonization of mesopsammal biotopes are structure and composition of the sediment. Quantitative investigations at List on Sylt reveal the Acoela speciesHaplogonaria syltensis andPseudaphanostoma psammophilum as being stenotope and stenobath.H. syltensis reaches population densities under favorable circumstances of up to 1500 individuals per 2.5 cm³. InHaplogonaria syltensis andPseudaphanostoma psammophilum annual population fluctuations are not attributable to their reproductive phases which depend upon the season; population decline during summer and displacement from optimal living spaces is due to the vigorous development of competing oligochaetes and archiannelides.     

Quantification of flow during suction feeding in bluegill sunfish

Nearly all aquatic-feeding vertebrates use some amount of suction to capture prey items. Suction prey capture occurs by accelerating a volume of water into the mouth and taking a prey item along with it. Yet, until recently, we lacked the necessary techniques and analytical tools to quantify the flow regime generated by feeding fish. We used a new approach; Digital Particle Image Velocimetery (DPIV) to measure several attributes of the flow generated by feeding bluegill sunfish. We found that the temporal pattern of flow was notably compressed during prey capture. Flow velocity increased rapidly to its peak within 20 ms of the onset of the strike, and this peak corresponded to the time that the prey entered the mouth during capture. The rapid acceleration and deceleration of water suggests that timing is critical for the predator in positioning itself relative to the prey so that it can be drawn into the mouth along with the water. We also found that the volume of water affected by suction was spatially limited. Only rarely did we measure significant flow beyond 1.75 cm of the mouth aperture (in 20 cm fish), further emphasizing the importance of mechanisms, like locomotion, that place the fish mouth in close proximity to the prey. We found that the highest flows towards the mouth along the fish midline were generated not immediately in front of the open mouth, but approximately 0.5 cm anterior to the mouth opening. Away from the midline the peak in flow was closer to the mouth. We propose that this pattern indicates the presence of a bow wave created by the locomotor efforts of the fish. In this scheme, the bow wave acts antagonistically to the flow of water generated by suction, the net effect being to push the region of peak flow away from the open mouth. The peak was located farther from the mouth opening in strikes accompanied by faster locomotion, suggesting faster fish created larger bow waves.     

Fish communities in temporarily open/closed estuaries from the warm- and cool-temperate regions of South Africa: A review

The majority of estuaries along the coastline of southern Africa are termed temporarily open/closed estuaries (TOCEs) and are closed off from the sea for varying periods by a sandbar which forms at the mouth. It is therefore important to understand the processes occurring within TOCEs and their importance to fishes in order to make sound management recommendations. Estuaries along the coast of South Africa and their associated fish assemblages are biogeographically distinct and occur in either a subtropical, warm-temperate or cool-temperate zone. There are 125 TOCEs found within the cool-temperate and warm-temperate zones. Most fish species found in TOCEs are the juveniles of marine taxa that breed at sea. Permanently open estuaries generally have a higher diversity of species than TOCEs, but TOCEs still provide important nursery areas for many marine species and numerically often have a higher proportion of estuarine resident species. Important taxa in terms of abundance and biomass in warm-temperate TOCEs include the sparids Rhabdosargus holubi and Lithognathus lithognathus, several mugilid species, estuarine residents (particularly Gilchristella aestuaria and Atherina breviceps) and the freshwater cichlid Oreochromis mossambicus. The diversity of fishes in cool-temperate TOCEs is low when compared with warm-temperate systems and Liza richardsonii tends to dominate catches by number and mass in most systems. Several species recorded in TOCEs show clear longitudinal distribution trends. For example Atherina breviceps is generally more abundant in the lower reaches of estuaries. Mouth state, particularly the frequency, timing and duration of mouth opening plays a key role in determining species richness, composition, diversity and abundance in TOCEs. Mouth state is directly linked to freshwater input. Reduced river inflow leads to prolonged mouth closure and shorter open phases, which inhibits immigration and emigration of marine fish species between estuaries and the sea. Understanding of the effects of various processes occurring within these systems, particularly variation in freshwater input, on the biota of these important systems facilitates the development of informed management recommendations.     

Biology of eelpout <Emphasis Type="Italic">Zoarces elongatus</Emphasis> (Zoarcidae) from Tauysk Bay,the Sea of Okhotsk

Based on the material collected in Tauysk Bay, the Sea of Okhotsk, from 1997 to 2014, the features of spatial distribution, body length and body weight composition, sex ratio, and some aspects of growth rate and reproduction of eelpout Zoarces elongatus are described. The representatives of the species prefer the biotopes with the littoral composed of large stones or pebbles, mainly from the upper border of the intertidal zone to the depths between 10 and 20 m. The catches mainly include the individuals with the body length 300?400 mm and body weight 0.1?100.0 g at the age between 5+ and 6+. Maximum registered body length, body weight, and age are as follows: 560.0 mm, 742 g, and 11+. The sex ratio (males: females) is 1: 1.2. In Tauysk bay, the release of juveniles occurs from November to December, and fecundity ranges from 20 to 185 eggs.     

Structure of the mouth opening and pharyngeal apparatus in three species of Baikal Cottoidei in relation to their feeding

The structure of the mouth opening and pharyngeal apparatus was studied, and its relation to the feeding pattern in three coastal species of Baikal Cottidae fish was analyzed. Analysis of data demonstrated that the general pattern of structure of the mouth opening and pharyngeal apparatus is similar in the species under study since their food is represented by bottom organisms, mainly by amphipods. Interspecies differences are manifested in an increase in relative values of morphological features and the size of consumed prey.     

Nearshore contagion and sampling of freshwater larval fish

The existence of larval fish contagion and its approximate magnitudein four different biotopes: at the shore of a river, surfaceand at fixed depth at an exposed coast of a large lake, andin a shallow, sheltered bay, was investigated, using passiveand active sampling. Non-random distributions were the rule;patchiness differed according to species, size, abundance anddiurnal movement, and was inversely related to distance fromshore. Characterization of contagion was hindered by samplingequipment and techniques, which were found wanting.     

Soil macrofauna of submediterranean ecosystems in the Abrau Peninsula,the Northwestern Caucasus

Submediterranean landscapes identified by geographers and botanists as a unique formation in the narrow coastal zone can also be distinguished according to soil-zoological characteristics. The fauna of large soil invertebrates has been studied in different forest types and open woodland of the Abrau Peninsula in July 2001. The results show that the distance from the sea plays the most important role in the formation of the soil macrofauna: its parameters in beech and hornbeam forests differ significantly from each other and from those in the coastal biotopes, in which the soil macrofauna is characterized by low abundance and contains a large proportion of xerophilic groups of invertebrates. The relict Haploembia solieri included in the Red Data Book can serve as an indicator species for this type of landscapes. Differences between the results of this study and the data obtained by Arnol’di and Gilyarov in 1958 are probably accounted for by geographic and seasonal factors rather than by anthropogenic transformation of the submediterranean ecosystems in the late 1950s.     

Behaviour and diet of sea trout post-smolts in a Norwegian fjord system

In order to study the behaviour of sea trout Salmo trutta L., in the early post-smolt phase, reared smolts were tagged with acoustic transmitters and released in the estuary of the River Aurland (Western Norway) and observed for 31–137·5 h. The study was conducted in May-June 1991 and 1995 on a total of seven tagged smolts. The fish moved back and forth along the littoral zone close to the surface and migrated net distances of 100–8000 m. In 1991 the tagged fish were usually observed in schools averaging 24–55 fish, while the tendency to school was less pronounced in 1995. Post-smolts of wild and reared origin were caught by 25 m long gillnets in the littoral zone. In 1991 the mean distance to shore at capture was 4·3 m and the mean depth 0·6 m, and the corresponding numbers in 1995 were 8·0 and 0·8 m. The distribution of the post-smolts is explained by a general preference for shallow water caused by osmoregulatory problems in high-salinity deep water, together with a preference for the sheltered littoral zone and a strong predation pressure in the open sea from fast swimming pelagic fish predators and gulls Larus sp. Schooling seemed to restrict predation by cod Gadus morhua L., in the littoral zone in 1991, while no cod were observed in this habitat in 1995. In both years the stomach contents of the netted fish consisted mainly of terrestrial insects. Reared fish chose prey items similar to those taken by wild fish, but consumed less food.     

Modelling Size-Dependent Cannibalism in Barramundi Lates calcarifer: Cannibalistic Polyphenism and Its Implication to Aquaculture

This study quantified size-dependent cannibalism in barramundi Lates calcarifer through coupling a range of prey-predator pairs in a different range of fish sizes. Predictive models were developed using morphological traits with the alterative assumption of cannibalistic polyphenism. Predictive models were validated with the data from trials where cannibals were challenged with progressing increments of prey sizes. The experimental observations showed that cannibals of 25–131 mm total length could ingest the conspecific prey of 78–72% cannibal length. In the validation test, all predictive models underestimate the maximum ingestible prey size for cannibals of a similar size range. However, the model based on the maximal mouth width at opening closely matched the empirical observations, suggesting a certain degree of phenotypic plasticity of mouth size among cannibalistic individuals. Mouth size showed allometric growth comparing with body depth, resulting in a decreasing trend on the maximum size of ingestible prey as cannibals grow larger, which in parts explains why cannibalism in barramundi is frequently observed in the early developmental stage. Any barramundi has the potential to become a cannibal when the initial prey size was <50% of the cannibal body length, but fish could never become a cannibal when prey were >58% of their size, suggesting that 50% of size difference can be the threshold to initiate intracohort cannibalism in a barramundi population. Cannibalistic polyphenism was likely to occur in barramundi that had a cannibalistic history. An experienced cannibal would have a greater ability to stretch its mouth size to capture a much larger prey than the models predict. The awareness of cannibalistic polyphenism has important application in fish farming management to reduce cannibalism.     

Species composition and dynamics of larval and juvenile fishes in the surf zone of Mauritius

The importance of the surf zone as a nursery ground for larval and juvenile fishes has been widely recognized, however the zone has yet to be studied in Mauritius. Recently, the coastal area of the island has been increasingly affected by human activities, especially by tourism. We collected fish samples with a hand pulled seine net during the period of August 2001 to March 2003 to clarify the fish fauna and the dynamics of fishes in the surf zone. Two sampling sites adjacent to river mouth areas and one sampling site adjacent to a mangrove area were selected for comparison of fish fauna in relation to environmental conditions. A total of 9,429 fish larvae and juveniles, representing at least 112 species from 48 families were collected. The abundant species were hardyhead silverside, Atherinomorus lacunosus, bluespot mullet, Valamugil seheli, and Ambassis spp., each contributing 16.2, 12.4, and 11.8% of the total number of individuals, respectively. Estuarine species dominated in the surf zone adjacent to the river mouth areas. Species composition and diversity changed seasonally. The number of fish increased during the rainy season. Species diversity increased at the turn of the seasons from the dry season to the rainy season. We conclude that species composition in each site was affected by environmental factors, such as the scale of the flux from the rivers, which is related to the precipitation. The results indicated that freshwater from the river is a trigger to aggregate larvae and juveniles in the surf zone.     

Occurrence of Larval and Early Juvenile Fishes in the Surf Zone Adjacent to two Intermittently Open Estuaries, South Africa

I monitored larval and early juvenile fishes in the surf zone adjacent to two warm temperate, intermittently open estuaries in South Africa. Mugilidae (59–67%) dominated fish assemblages in the surf zones adjacent to the Van Stadens and Kabeljous estuaries. Other dominant families included the Atherinidae, Sparidae and Soleidae. The most abundant species caught during the study were the catadromous mugilid Myxus capensis, in a postflexion or early juvenile stage of development, and the sparid Rhabdosargus holubi, in a postflexion stage of development. Species displaying a degree of dependence on estuaries during the early phase of their life cycle dominated (96–98%) surf zone catches. Most fish encountered were at the postflexion stage of larval development. Larval and early juvenile fishes were more abundant during the summer and autumn months with density peaking several-fold during natural estuary opening events, particularly in the surf zone adjacent to the Kabeljous Estuary. Decreases in salinity showed a significant relationship with increases in fish density during a March opening event in the surf adjacent to the Kabeljous Estuary where catches were concentrated along a current-driven estuarine plume. Catches adjacent to the Van Stadens Estuary also increased considerably during two smaller opening events in March and November although salinity played no statistically significant role in these increased catches. Results from the surf adjacent to the Van Stadens Estuary suggested that either very small amounts of estuarine water entering the surf zone can elicit an accumulation response by estuary-dependent larval and early juvenile fishes or that an additional characteristic of estuary/river water, other than salinity per se, is aiding the cueing process.     

On the biology of rockfishes Sebastes minor and S. taczanowskii (Sebastidae) from the coastal waters of northern Primorye

Based on the materials from 1998–2004, the distribution, size and weight composition, growth, dates of reproduction, and the quantitative composition of the food of rockfishes Sebastes minor and S. taczanowskii from the coastal waters of northern Proimorye are considered. It is shown that in the coastal biotopes Sebastes minor prefer sites at the boundaries between sand and reefs with algal vegetation, while S. taczanowskii prefers a rather deep part of the reefs. S. minor reaches the length of 18 cm, weight of 85 g, and the age of 10 years; S. taczanowskii reaches 21 cm, 160 g, and 8+, respectively. The rate of growth in both perches is at its maximum in the first three years of life. S. minor is a zooplanktophage (it feeds mainly on copepods and amphipods); S. taczanowskii is a polyphage (it more often eats amphipods, decapods, and juvenile fish).     

Biological and chemical responses in a temporarily open/closed estuary to variable freshwater inputs

In coastal lagoons with occasional connection to oceans, variations in physicochemical conditions and biological responses can be pronounced. To examine the influence of variable rainfall and tidal flushing, we measured, over a 4-year period, salinity, temperature and dissolved oxygen, and fish abundances, in Devereux Slough, a coastal lagoon occasionally connected to the Pacific Ocean along the California coast. We test the hypotheses that salinity is the primary influence on fish composition, and that fish density is affected by freshwater discharge and by berm breaches. During our sampled years, annual rainfall varied from 188 to 971 mm, and the sand berm separating the Slough from the ocean breached in each year except 2007, a drought period. Average yearly salinity ranged from 7.7 to 37.1 ppt. Hypoxic conditions in the near-bottom water were common each year. The best predictor of the fish composition was salinity, and an indirect correlation with fresh water discharge was responsible for much of the temporal variation in the fish assemblage. The interaction between salinity, state of the estuary mouth (open vs. closed), and precipitation significantly predicted densities of Fundulus parvipinnis (Girard 1984).     

Can stable isotopes be used to infer site fidelity of nekton in open coastal areas?

Stable isotope analysis has been applied to the investigation of movement in several species, including marine animals. However, its application to nekton living in open coastal areas is still very scarce. This study aims to test if stable isotope analysis can be used for this purpose over a much wider spatial scale than previously investigated. Stable isotope analysis was used to 1) investigate isotopic variation in shrimp and fish, in 11 sites, along a 160 km coastal stretch, to 2) determine the site fidelity of the individuals within each species, and to 3) test the relation between the body size of the individuals within each species, at each site and the percentage of isotopic deviants. Site fidelity was the highest for the intertidal fish Gobius paganellus and Coryphoblennius galerita, with 60% and 64% of individuals considered residents, respectively, and lowest for the demersal fish Diplodus vulgaris and Diplodus sargus with 23% and 33% of resident individuals, respectively. The percentage of isotopic deviants was not correlated with length in any species. Site fidelity was considerably higher than that previously found for other open coastal areas and similar to more structured environments, like coastal ponds. It was hypothesized that the complex tri-dimensional structure of the rocky reefs that occur in this area, often encompassing channels and tide pools, offers conditions favourable to high site fidelity. This study shows that stable isotopes can be used to infer nekton movement in wide open coastal areas.     

Distribution,population structure,and some biological distinctions of pikeperch <Emphasis Type="Italic">Sander lucioperca</Emphasis> of the channel part of the Akhtuba River (Volga-Akhtuba water system)

Biological traits (distribution, reproduction, age composition, body length and weight) of pikeperch Sander lucioperca from channel parts of the Akhtuba River, remote from the Volga Delta, are investigated. In the investigated stretch of the river, movements of most specimens of pikeperch are local and occur in the deep part (4?10 m) of the channel. Aggregations of fish are not confined to any definite points but move along the extensive stretch of broads. Pikeperch prefer near-bottom biotopes confined to the zone of stable hydrodynamic eddies in places of complicated bottom relief—transverse crests and longitudinal channel crests. For the first time, it is found that pikeperch in the under-ice period move to the shallow zone of submersed inshore shrubs. The age structure and body length and weight of pikeperch differ from those in the Volga Delta and correspond more to the populations from northern and northwestern parts of the species area. Pikeperch spawn only in temporary water bodies of the accessory system, within a short period at the temperature 11?17°С. The data on biology of pikeperch from the Akhtuba channel indicate the populational level of differences from the Volga Delta pikeperch.     

Distribution of frit flies (Chloropidae: Meromyza Mg.) in Vologda oblast and East Poland

Species diversity and abundance of frit flies from the genus Meromyza have been assessed in coastal biotopes, grasslands, and agro-ecosystems of Vologda oblast (Russia) and Warsaw province (Poland). The Jaccard quotient of similarity (IG) of frit fly abundance has shown a uniformity between coastal banks and grasslands along these banks, as well as between cultivated cereals (except for oats) and field boundaries, cultivated fields, and some reach-in-herbs grasslands, including hayfields. Considerable heterogeneity of species composition of the flies has been revealed in similar biotopes. The biotopes studied have been found to be dominated by one species of frit flies. It has been discovered that cereal rotation in agro-ecosystem results in change in the dominant species of frit fly. The cereal height has been found to influence the abundance and diversity of frit flies. No regularities have been observed in the correlation between the abundances of frit flies in different biotopes. It has been pointed out that M. nigriseta Fed. and M. variegata Mg. can feed on cultivated cereals.     

Ontogenetic shift in mouth opening mechanisms in a catfish (Clariidae, Siluriformes): a response to increasing functional demands

During ontogeny, larval fish have to deal with increasing nutritional and respiratory demands as they grow. As early ontogeny is characterized by an increasing complexity of moving structural elements composing a fish skull, some constraints will have to be met when developing mechanisms, which enable feeding and respiration, arise at a certain developmental stage. This article focuses on the presence/absence of a possible functional response in mouth opening during ontogeny in Clarias gariepinus. Some reflections are given, based on morphological data, as well as related function-analysis data from the literature. Starting shortly after hatching, a total of up to five different mouth opening mechanisms may become functional. Of these, three may remain functional in the adult. As could be expected, the apparatuses that enable these mechanisms show an increase in complexity, as well as a putative improvement in mouth opening capacity. Initially, two consecutive mechanisms may allow a restricted depression of the lower jaw (both passively and actively). Synchronously, two more mechanisms may arise, which involve the coupling of the hyoid depression to the mouth opening. At about 11 mm SL a fifth mechanism becomes established, better known as the opercular mouth opening mechanism. An overlapping chronology of functionality of the different mechanisms, as well as differences in efficiencies, could be an indication of the absence of a true critical period in C. gariepinus (at least in relation to mouth opening), as well as the possible presence of a shift in feeding type. Finally, the coupling of the chronology of the shift in mouth opening mechanisms and several morphological, behavioral, and physiological changes during ontogeny, related to feeding and respiration, make it possible to distinguish five important phases in the early life history of C. gariepinus.     

Changes in the abundance and diversity of coastal wetland fauna from the open water/macrophyte edge towards shore

Great Lakes coastal wetlands are widely recognized as areas of concentrated biodiversity and productivity, but the factors that influence diversity and productivity within these systems are largely unknown. Several recent studies have suggested that the abundance and diversity of flora and fauna in coastal wetlands may be related to distance from the open water/macrophyte edge. We examined this possibility for three faunal groups inhabiting a coastal wetland in Saginaw Bay, Lake Huron. We sampled crustacean zooplankton and benthic macro-invertebrates at five distances from open water in the summer 1994, and fish at three distances from open water in 1994 and 1995. We found significant spatial trends in the total abundance and diversity of zooplankton and fish, as well as the diversity of benthic macro-invertebrates. Zooplankton abundance and taxa richness were highest at intermediate distances from open water in a transition zone between the well-mixed bayward portion of the wetland, and the non-circulating nearshore area. Benthic macro-invertebrate taxa richness increased linearly with distance from open water. In contrast, fish abundance and species richness declined linearly and substantially (abundance by 78%, species richness by 40%) with distance from open water. Of the 40 taxa examined in this study, 21 had significant horizontal trends in abundance. This led to notable differences in community composition throughout the wetland. Our results suggest that distance from open water may be a primary determinant of the spatial distributions of numerous organismal groups inhabiting this coastal wetland. Several possible reasons for these distributions are discussed.