Estuarine fish behavior around slotted water control structures in a managed salt marsh

Estuaries are composed of multiple interconnected habitat types used by transient fish species during their period of estuarine residency. Structural marsh management restricts habitat connectivity and impedes the movement of fishes among these habitat types by limiting access via water control structures (WCSs) between the managed area and the rest of the estuary. While some general information on fish passage rates is available, species-specific information on passage through WCSs is lacking for salt marsh fishes. We monitored tagged fishes from March 2012 through November 2013 using passive integrated transponder antenna arrays at two identical WCSs in the Calcasieu Lake estuary, Louisiana, USA, to assess the effect of slotted WCSs on fish behavior. A total of 420 individuals of 15 species was tagged and released at the WCSs; of these, 145 individuals representing 11 species were later detected at the WCSs. Five species comprised most (93%) of the detected individuals: Elops saurus (n = 60), Mugil cephalus (n = 43), Sciaenops ocellatus (n = 20), Pogonias cromis (n = 7), and Ariopsis felis (n = 5). Passage rates were low, with most of the observed fishes (n = 80) passing only once through the structures. Other than E. saurus, which was only observed migrating out of the managed marsh, no clear pattern in swimming direction was observed for the other species. Detected species were all present primarily during the summer and fall, however, diel activity at the structures varied by species. The WCSs in our study area appeared to attract and congregate fishes, functioning more like ecological hotspots, rather than simply facilitating fish passage.     

Fish production in estuaries of Primorye

Production of fish communities in 15 different-types estuaries was assessed based on the data collected as a result of 90 surveys (860 seine stations) conducted in Primorye in 2002–2015. The main contribution to production was made by semi-anadromous species (the so-iuy mullet Liza haematocheilus, Far Eastern redfins Tribolodon spp., and Japanese smelt Hypomesus nipponensis, etc.). In both external (EP _ext) and internal (EP _int) polyhaline estuaries (EP) a substantial portion of the production was provided by resident marine species (mainly by the saffron cod Eleginus gracilis, Far Eastern smooth flounder Liopsetta pinnifasciata, and tidepool gunnel Pholis nebulosa) and southern immigrants (flathead grey mullet Mugil cephalus, dotted gizzard shad Konosirus punctatus, Japanese halfbeak Hyporhamphus sajori, and Pacific needlefish Strongylura anastomella). In mesohaline (EM) and oligohaline (EO) estuaries, the proportion of marine residents and southern immigrants was reduced to a minimum, while that of freshwater species (bighead gudgeon Gobio macrocephalus, Prussian carp Carassius gibelio, minnow Phoxinus spp., Amur bitterling Rhodeus sericeus, spiny bitterlings Acanthorhodeus spp., etc.) substantially added to the production of semi-anadromous fish. The mean fish biomass for the vegetation season varied in the 143–1463 mgC/m² range; the mean annual production was 174–4267 mgC/m² and the mean P/B ratio was 0.2–3.2. In 2007, the high annual production in the Artemovka River estuary, 9356 mgC/m², was formed by the juvenile so-iuy mullet of the strong yearclass that hatched in 2006. The lowest mean production and P/B values were typical mainly for the water bodies with a salinity more often close to that of the barrier zones (5–8‰ for α-horohalinicum and 22–26‰ for β-horohalinicum), i.e., for EM and EP _ext. This relationship is explained by the features of the osmotic regulation in fish of various origins and its ontogenetic variations. In particularly, the salinity in EM is more frequently close to the critical salinity (5–8‰, α-horohalinicum); thus, the proportion of juveniles of most of the species in the catches decreases (as their resistance to salinity variations is lower). This results in higher mean values of the specific and absolute production of fish communities in EP _int and EO as compared to those in EM. The conclusion was made that the estimates of fish production in the estuaries of Primorye are similar to those in the well-studied estuaries of the temperate, subtropical, and tropical zones. Moreover, they are comparable to the fish production estimates for mesotrophic and eutrophic lakes in northwestern Russia, substantially lower than those for large lowland rivers, and higher than those for small rivers. The fish production in seas, including the Japan/East Sea (0.20 gC/m²) and, particularly, Peter the Great Bay (0.28 gC/m²), is mostly lower than that in Primorye estuaries.     

Morphological and behavioral ontogeny in larval and early juvenile discus fish <Emphasis Type="Italic">Symphysodon aequifasciatus</Emphasis>

We observed the growth, morphological changes, and behavior of larvae and juveniles of the Amazonian substrate-brooding cichlid discus fish Symphysodon aequifasciatus under laboratory conditions. The mean body length (BL) of newly hatched larvae was 3.4–3.5 mm, and the yolksac extended to approximately 42 % of their BL. Larvae detached from the substrate on day 4 began swimming and immediately displayed biting behavior on the body surface of the parents. Larvae had completely consumed their yolksacs by day 7. They began swimming at an earlier developmental stage compared with other cichlid species. Their thick lips may be advantageous for removing mucus from the bodies of the parent fish. Juveniles actively fed on Artemia spp. by day 30, and the frequency of biting behavior toward the parents decreased between days 20 and 35. Bone ossification was essentially complete in juveniles by day 32. Juveniles reached 16.0 ± 1.1 mm BL by day 35. These results indicate that the morphology and behavior of larval and early juvenile S. aequifasciatus exhibit adaptations for mucus provisioning.     

Habitat partitioning in juvenile fishes associated with three vegetation types in selected warm temperate estuaries,South Africa

Three common vegetation types were studied to assess habitat partitioning in juvenile fishes in select warm temperate estuaries of South Africa. Vegetated habitat types are known as productive and important areas for predator avoidance and feeding and are often preferred by juvenile fishes. Habitat partitioning is not well understood, with previous studies mostly focusing on seagrass (Zostera capensis). This study aimed to assess three common vegetated fish nursery areas in estuaries to aid conservation planning. Fishes were collected by means of double-winged, six-hooped fyke nets, 1 mm mesh size secured in placed on the nocturnal flood tide at each inundated vegetation type (Phragmites australis, Zostera capensis, Spartina maritima) and at an adjacent unvegetated site for three consecutive months in 2014 and 2015 during the summer recruitment period for juvenile fishes. Higher catches were frequently recorded in vegetated areas for solely estuarine and marine estuarine dependent species. In general, the previously unstudied reed, P. australis showed the highest species richness and abundance of juvenile fishes overall, followed by, Z. capensis and the intertidal salt marsh species, S. maritima. Results from this study supports international trends on the value of vegetated areas as refugia for young fishes in estuaries.     

Organic matter sources for fish larvae and juveniles in a marine-estuarine interface (Mar Chiquita lagoon,Argentina)

The aim of this study was to analyze the organic matter (OM) origin in the nearshore and the surf zones adjacent to Mar Chiquita lagoon, in order to determine the importance of allochthonous estuarine detritus and in situ marine phytoplankton as carbon (C) sources for young fishes prior to entering the lagoon. Water samples from both the nearshore and the surf zones were collected for estimation of Chlorophyll a concentration, and δ¹³C and δ¹⁵N values of the particulate organic matter (POM). Isotopic composition of the zooplankton and fish larvae from both zones and fish juveniles from the surf zone were also estimated. The contribution of potential OM sources was quantified by Bayesian stable isotope mixing models (SIAR). SIAR models revealed that the POM composition in the coastal area close to Mar Chiquita lagoon comprised a mix of primary producers (terrestrial and marine). The cordgrass Spartina densiflora that develops in the saltmarshes bounding the lagoon, contributed most to the POM of the surf zone, being important as a C source for zooplankton from the same zone. Towards deeper waters (10–12 m, ~2.5 km offshore) with higher chlorophyll a concentrations, phytoplankton contributed most to the POM. Spartina densiflora was not relevant as a C source for larval and juvenile fishes. However, it was of importance to the group of primary consumers, which apparently sustain other zooplankton organisms that fish fed on. In this sense, the OM derived from S. densiflora and exported to the coastal area contributes to sustaining the prey for young fishes outside Mar Chiquita.     

Locomotor synergies in fish

The kinematic characteristics {f(v), A(v), w(v)} allow a first-approximation representation of locomotor synergies in the swimming of fish: f is the frequency of the transverse oscillations, A is the amplitude of the caudal fin sweep, w is the velocity of the locomotor wave, and v is the locomotion speed. The additional compared characteristics included the step length L(v) and the wavelength λ(v), where L ≡ vT is the distance covered by the fish during the period T ≡ 1/f, and λ ≡ wT. These kinematic characteristics were derived from video recordings of swimming in six fish species. Three of the species investigated belonged to the anguilliform type, while the three others belonged to the carangiform type. The constant value of the wavelength λ at all speeds v was the common feature of the two types. The anguilliform fish performed a oneparameter version of locomotion control: the locomotion speed v changed due to the change of the wave velocity w and the undulatory amplitude remained constant. The carangioid fish used a two-parameter version of control, with changes in both the wave velocity w and the amplitude of undulations of the body and tail fin.     

Alterations in Digestive Enzymes of Three Freshwater Teleostean Fishes by Almix Herbicide: A Comparative Study

Three freshwater teleostean fishes viz., Anabas testudineus (Bloch), Heteropneustes fossilis (Bloch) and Oreochromis niloticus (Linnaeus) were exposed to almix (66.67 mg/l) herbicide for 30 days to investigate the activity of digestive enzymes (amylase, lipase and protease) in stomach, intestine and liver. Amylase activity showed significantly high (p < 0.05) in all the fishes compared to control value and highest activity was observed in liver of A. testudineus (721.99 %) and minimum in intestine of H. fossilis (195.37 %). Lipase activity was also significantly increased (p < 0.05) in all the tissues; but highest in intestine of O. niloticus (235.51 %) and minimum in intestine of A. testudineus (130.51 %). Protease activity also showed similar trends of enhancement; it was maximum in stomach of O. niloticus (362.69 %), whereas in liver of H. fossilis it was rather less (173.72 %). Increased activity of digestive enzymes resulting from tissue damage ultimately affected the fish health due to impairment of digestive physiology confirming the herbicidal contamination on fish species. The sensitivity to the almix herbicide was pronounced in the order of O. niloticus > A. testudineus > H. fossilis.     

Abundance,distribution, and territory areas of rock-dwelling Lake Tanganyika cichlid fish species

Lake Tanganyika, the second-oldest and second-deepest lake in the world, harbors an impressive cichlid fish fauna counting about 250 endemic species that are characterized by a great level of ecological, morphological, and behavioral specialization. This study describes and compares cichlid fish communities at two rocky shores with differential human impact in the south of Lake Tanganyika. Species inventories and depth-dependent abundances were elaborated. About 41 and 46 sympatric cichlid species were recorded in the two study sites, respectively. Variabilichromis moorii was the most abundant species (29–60% of total number of fishes), followed by Aulonocranus dewindti (3–19%), Tropheus moorii (12%), Ophthalmotilapia ventralis (4–10%), Eretmodus cyanostictus (6–11%), and Cyathopharynx furcifer (0.01–9%). All other species had abundances below 5%. It further emerged that large cichlids such as Petrochromis species, Cyathopharynx furcifer, and Lobochilotes labiatus were very rare at one location, with frequencies of 0.55% or less. Territorial sizes of three particularly abundant species, Variabilichromis moorii, Aulonocranus dewindti, and Tropheus moorii, were assessed by behavioral observations. We distinguished between territorial core areas and total defended area, yielding average core areas between 0.4 (V. moorii) and 1.6 m² (T. moorii), and total defended areas averaging for each species between 1.6 (V. moorii) and 5.0 m² (A. dewindti) with no significant differences between the two study sites. The data on individual densities are also relevant for evolutionary studies, in that they allow more accurate calculations of effective population sizes.     

Patterns of distribution and movement of fishes, <Emphasis Type="Italic">Ophthalmolepis lineolatus</Emphasis> and <Emphasis Type="Italic">Hypoplectrodes maccullochi</Emphasis>, on temperate rocky reefs of south eastern Australia

Current ecological models predict that reef fish assemblages will be strongly influenced by habitat type. Here we test hypotheses about habitat types and abundance patterns of temperate reef fishes from broad spatial scales (100 s of km) to small spatial scales of metres to tens of metres. Habitat preferences are also described over long periods of time (22 years) for two abundant taxa. Patterns of distribution and abundance varied over ～ eight degrees of latitude (29.9–37.5°S) along the coast of New South Wales, Australia. Ophthalmolepis lineolatus (Labridae) preferred kelp and Barrens habitats and juveniles were most abundant in habitats rich in algae. This species also increased in abundance from North to South. In contrast, Hypoplectrodes maccullochi (Serranidae) were usually only found in the Barrens habitat and great variation was found among locations. Both taxa were most abundant on urchin grazed deep reefs (over 10 m deep). Habitat preferences of O. lineolatus and H. maccullochi appeared resistant to major environmental perturbations that included large El Niño events in 1991, 1998 and 2002. Home ranges of O. lineolatus varied from 52 m² to 1,660 m² and often overlapped; fish of all sizes were most abundant in algal dominated habitat. Limited movements and small home ranges (2.1–11.6 m²) combined with a strong affiliation for shelter indicated that most H. maccullochi are strongly site-attached. Habitat type is important to these taxonomically different fishes, but to varying degrees where H. maccullochi was more of a habitat specialist than O. lineolatus and would be more vulnerable to perturbations that alter Barrens. Changes in reef habitats will have a great influence on fish assemblages and this should also be considered in coastal planning (e.g. for Marine Protected Areas, MPAs) and the assessments of resistance and resilience of fishes to climate change.     

Fish assemblage structure in an estuary of the Atlantic Forest biodiversity hotspot (southern Brazil)

We described the fish assemblage in the estuary of the Guaraguaçu River (one of the largest tributaries of the Paranaguá Bay Estuary, located within Brazil’s Atlantic Forest Biosphere Reserve) from June 2005 to May 2006, and assessed the seasonal and spatial effects of abiotic environmental attributes on the fish assemblage structure. Despite some oscillations in salinity, the upper and lower estuaries had year-round persistent oligohaline and polyhaline conditions, respectively. Despite high species richness (55 species), the Guaraguaçu River Estuary fish community contains a few dominant taxa; 11% of the richness accounts for >60% of its density and biomass. The most abundant species (in terms of both biomass and density) was Atherinella brasiliensis. Species whose densities were most strongly associated with the upper estuary were Centropomus parallelus, Ctenogobius schufeldti, Eucinostomus melanopterus, Platanichthys platana, Trinectes paulistanus, and Eugerres brasilianus. Those whose densities were most strongly associated with the lower estuary were A. brasiliensis, Sphoeroides greeleyi, Eucinostomus argenteus, Sphoeroides testudineus, Diapterus rhombeus, and Harengula clupeola. Throughout the year, canonical correspondence analysis identified: (1) the pattern of horizontal stratification of salinity along the river as being the most important variable for explaining most of the fish fauna structure; and (2) a strong relationship between the fish fauna and the salinity gradient along the estuary. Analysis of similarity further confirmed that each estuarine zone supports a year-round persistent and relatively homogeneous fish species assemblage. Total mean density and biomass remained constant over time in each estuarine habitat, but density shifted in the most abundant species, which appears related to recruitment patterns. Such species and abundance persistence likely occurs because seasonal rainfall-induced changes in river discharge are not sufficient to significantly shift runoff and salinity and thus fish assemblage structure (species composition, density and biomass) along the estuary. Such a lack of seasonal fish fauna movement as a response to changes in river flow contrasts with other estuarine systems around the world.     

Strategies of resource partitioning between two sympatric puffer fishes in a tropical hypersaline estuary,Brazil

The strategies of food partitioning among two abundant estuarine puffer fishes, Sphoeroides greeleyi (Gilbert, 1900) and Sphoeroides testudineus (Linnaeus, 1758), were investigated in a tropical hypersaline estuary. We examined the stomachs of 946 fishes collected with a beach seine across three zones (upper, middle and lower estuary) along with a salinity gradient. The highest abundances of species were recorded in the upper and middle estuary. The diet was comprised mostly by benthic organisms, mainly Bivalvia, Gastropoda, and Brachyura. However, in a hypersaline estuary, these species develop strategies of resource partitioning in three ways: 1) asymmetry effects; 2) habitat selection; and 3) trade-offs among age classes. Diet variations according to fish age classes indicated that the largest individuals showed a decrease in their consumption of small preys (Amphipods, Copepods, and Ceratopogonidae) and an increase in their consumption of larger preys (Bivalvia and Decapoda). This behavior of switching diet towards larger prey was related to the functional trade-offs in swimming capacity, and feeding mode used to capture prey. The middle and upper estuary are important feeding grounds for puffer fishes, as demonstrated by their influence on prey distributions and habitat type. Diet breadth indicated that S. greeleyi tended to be a generalist, whereas S. testudineus tended to be a specialist. Thus, the strategies of partitioning seem to have importance for puffer fish populations in this hypersaline environment.     

Biological features of the common fish species in Olyutorsky-Navarin region and the adjacent waters of the Bering Sea: 4. family sculpins (Cottidae)

Based on the materials of investigations conducted for 20 years (1995?2015), the features of biology of the common fish species of the family Cottidae from the northwestern Bering Sea are studied. These species are found during summer and fall in the waters of the Olyutorsky-Navarin region. The size–age parameters of the fishes collected with different fishing gears, as well as the features of their body length and body weight dynamics, spawning time, and spawning conditions, are described. The largest exemplars of shorthorn sculpin Myoxocephalus verrucosus and staghorn sculpins, armorhead sculpin Gymnocanthus galeatus and G. detrisus, are recorded in the catches of snurrevads, while the fishes caught in trawls are characterized by smaller size. Interannual variability of the size composition of the fish is related to the abundance of certain generations or to the fishery directed to different associations of sculpins. In the coastal waters, comparatively low average body size is usual for the majority of common sculpin species (with the exception of lords, yellow Irish lord H. jordani and Gilbert’s Irish lord H. gilberti) because of the dominance of juveniles.     

Findings of new and rare fish species in the coastal zone of the Crimea (the Black Sea)

Characteristics of seven Atlantic-Mediterranean fish species are provided. Of them, four (gobies—yellow-headed Gobius xanthocephalus and red-mouthed G. cruentatus, incognito blenny Parablennius incognitus, and greater pipefish Syngnathus acus) were either first found in the Black Sea coastal zone of the Crimea, or their findings were doubted, and three species (thin-lipped grey mullet Liza ramada, European barracuda Sphyraena sphyraena, and Black Sea salmon Salmo trutta labrax) are very rare. Over the last decade, the authors recorded 15 fish species; of them, seven Atlantic-Mediterranean species have dispersed along the Crimean coasts by now, one endemic of the far eastern seas (chameleon goby Tridentiger trigonocephalus) has naturalized in Sevastopol Bay, four invading species, freshwater by origin, permanently occur in the estuary zones of the peninsula; the remaining three species are known from single findings and apparently belong to the category of accidental fish. An increase in the species composition of ichthyofauna off the Black Sea coasts of the Crimea results from the on-going process of mediterranization—the invasion in the estuary of freshwater tolerant species at the expense of accidental species that penetrated here either independently or with ballast waters.     

The effect of size on juvenile green sturgeon (<Emphasis Type="Italic">Acipenser medirostris</Emphasis>) behavior near water-diversion fish screens

Anthropogenic water management projects and facilities that alter the local and regional hydrology of riverine environments greatly influence the behavior, physiology, and survival of native fishes. To mitigate for losses of native fishes at these structures, many are outfitted with fish-exclusion screens to reduce entrainment. The effect of fish size and age on behavior near fish screens, however, is largely unknown. Therefore, we tested two size classes of juvenile green sturgeon (Acipenser medirostris; small, early juveniles: 9.2 ± 0.2 cm fork length [FL], 6.9 ± 0.3 g; intermediate juveniles: 18.8 ± 0.2 cm FL, 36.9 ± 0.8 g) near fish-exclusion screens in a laboratory swimming flume. Although size was a significant factor influencing the way in which fish contacted the screens (i.e., proportion of body contacts, p = 2.5 × 10^?9), it did not significantly influence the number of times fish contacted screens or the amount of time fish spent near screens. We also compared the performance of these two size classes to that of older and larger sturgeon that were tested previously (29.6 ± 0.2 cm FL, 147.1 ± 3.1 g), and documented a clear difference in the behavior of the fish that resulted in disparities in how the large fish contacted screens relative to small- or intermediate-sized juveniles (p = 0.005, 5.4 × 10^?4, respectively). Our results further our understanding of how ontogeny affects fish behavior near anthropogenic devices, and are informative for managers seeking to identify the most susceptible size and age class of juvenile green sturgeon to water-diversion structures to potentially develop size-specific conservation strategies.     

Distribution and abundance of fish in the southwest of Caspian Sea coastal waters

This study was carried out in southwestern Caspian Sea coastal area to elucidate demersal bony fishes distribution and abundance. Twenty two species were found in shore line, which belong to 6 families. In deeper waters down to 7 meters only 5 species of Gobiidae and 1 species of Syngnathidae were identified. Two species Neogobius caspius and N. pallasi were the main components of demersal fishes; however in some regions Rutilus caspicus, Rutilus kutum and Liza spp. were dominated. Most places were dominantly occupied by Atherina boyeri, which had the highest abundance among the pelagic fishes. Conversely, the Ponticola gorlap, N. melanostomus and Proterorhinus nasalis showed the lowest abundances (less than 1 ind./100 m²). Benthophilus stellatus and P. nasali had the lowest niche overlaps with other species. Both of these two species and P. gorlap are suggested to be classified as endangered or vulnerable species based on their low abundance. The distribution of Syngnathus abaster depends on algae, while algae grow up into the stony construction of the coastal line. A negative insignificant correlation was observed between pelagic and demersal fish abundances. The commercial fisheries data of 76 beach seines in our study area during 2002–2013 was compared with our results on fish abundance and species composition. More than 93% of total fish catch constituted Liza spp. and Rutilus kutum. The relationship between the abundance and distribution of the studied species, and the restocking activities performed by Iranian fisheries organization are discussed. The high abundance and distribution of small size fish in tidal zone could be related to the distribution of crustacean, which provide a good source of food for these fish species.     

Mass immigration of juvenile fishes into a small,once-dried tributary demonstrates the importance of remnant tributaries as wintering habitats

The winter ecology of stream fishes is still poorly understood, especially in non-salmonid species. A small tributary (<4 m in width, <1 km in length) of the Otofuke River (central Hokkaido, northern Japan) dewatered in the summer of 2013, which allowed us to evaluate immigration after the summer draught. More than 10000 juveniles of Siberian stone loach Barbatula toni, Japanese dace Tribolodon spp., and non-native rainbow trout Oncorhynchus mykiss immigrated to the tributary in the four months following the summer dewatering. This suggests that even remnant tributaries may be critical wintering habitats for some juvenile fishes.     

Comparison of the methods applicable for the pathogenicity assessment of entomopathogenic nematodes

Single infective juveniles of Heterorhabditis bacteriophora, H. megidis (Nematoda: Heterorhabditidae), Steinernema arenarium, S. carpocapsae and S. feltiae (Nematoda: Steinernematidae) were used to infect single Galleria mellonella (Lepidoptera: Pyralidae) larvae. Four parameters of entomopathogenic nematodes pathogenicity were assessed: the mortality of insects, infectivity of nematodes, number of nematodes established per single G. mellonella, and degree of infective juveniles colonization (percent of infective juveniles which intestine was colonized by symbiotic bacteria). The accuracy, repeatability, and versatility for different species of EPNs in bioassay arenas were compared. Our modifications of the original methods yielded ~ 50% higher efficiency of infective juveniles in cell culture plates and > 20% higher efficiency in centrifuge test tubes. The efficiency of nematodes in cell culture plates (39–77%) was relatively low, especially in the case of Heterorhabditis spp. In the bioassay arena, infective juveniles migrated between cells. The results of our studies indicate that the pathogenicity of EPNs should be assessed in centrifuge test tubes. In these arenas, the infectivity of single IJs was ~ 90% for Heterorhabditis spp. and ~ 95% for Steinernema spp. The degree of colonization of the EPN isolates by symbiotic bacteria was in the range of 96–98%.     

Climate-driven coral reorganisation influences aggressive behaviour in juvenile coral-reef fishes

Globally, habitat degradation is altering the abundance and diversity of species in a variety of ecosystems. This study aimed to determine how habitat degradation, in terms of changing coral composition under climate change, affected abundance, species richness and aggressive behaviour of juveniles of three damselfishes (Pomacentrus moluccensis, P. amboinensis and Dischistodus perspicillatus, in order of decreasing reliance on coral). Patch reefs were constructed to simulate two types of reefs: present-day reefs that are vulnerable to climate-induced coral bleaching, and reefs with more bleaching-robust coral taxa, thereby simulating the likely future of coral reefs under a warming climate. Fish communities were allowed to establish naturally on the reefs during the summer recruitment period. Climate-robust reefs had lower total species richness of coral-reef fishes than climate-vulnerable reefs, but total fish abundance was not significantly different between reef types (pooled across all species and life-history stages). The nature of aggressive interactions, measured as the number of aggressive chases, varied according to coral composition; on climate-robust reefs, juveniles used the substratum less often to avoid aggression from competitors, and interspecific aggression became relatively more frequent than intraspecific aggression for juveniles of the coral-obligate P. moluccensis. This study highlights the importance of coral composition as a determinant of behaviour and diversity of coral-reef fishes.     

Study on properties and regulation peculiarities of glycogenolysis enzymes in fish skeletal muscles depending on peculiarities of the species motor activity

The activity values, properties and peculiarities of activation of glycogen phosphorylase (GP, EC 2.4.1.1) and glycogen phosphorylase kinase (GPK, EC 2.7.138) were studied in the white skeletal muscle of fishes differing in motor behavior. No differences in the GP and GPK activity levels were revealed in porgy Diplodus annularis (L.), horse mackerel Trachurus mediterraneus ponticus, trout Salmo trutta morphario, scorpionfish Scorpaena porcus, flounder Scophtalnus maeoticus maeoticus, and carp Cyprinus carpio; however, properties of the isolated enzymes and peculiarities of formation of their activated forms during swimming in a hydrodynamic tube are determined by functional peculiarities of the muscle tissue and are associated with the motor activity character of the species. The more rapid ion regulation prevails in fishes capable for the burst swimming type (scorpionfish, trout). The glycogenolysis hormonal regulation leading to a change of the GPK activity index has been found in other species.     

Feeding capability of black scraper <Emphasis Type="Italic">Thamnaconus modestus</Emphasis> on giant jellyfish <Emphasis Type="Italic">Nemopilema nomurai</Emphasis> evaluated through field observations and tank experiments

Although many fish species are known to feed on jellyfish, only a few quantitative studies on this subject have been conducted in the field or laboratory. We combined field observations and feeding experiments to quantitatively evaluate the potential feeding capability of the black scraper Thamnaconus modestus on giant jellyfish Nemopilema nomurai in a jellyfish-abundant area. Underwater observations revealed that shoals of T. modestus fed voraciously on jellyfish when the jellyfish were close to the fish’s seaweed habitat. Gut contents of field-collected T. modestus almost exclusively consisted of jellyfish. In tank trials, feeding activity of black scraper was high when light intensity was between about 1.1 lx and 50 × 10³ lx. The estimated feeding speed of T. modestus on the jellyfish in the Sea of Japan when the jellyfish bloom occurred was 10.0 ± 2.0 times fish body weight per day. The results support the prediction that T. modestus and probably other coastal medusivorous fishes have a substantial capability to eliminate jellyfish blooms. Considering that they are highly dependent on seaweed bed, protection of such habitats for these medusivores may be the most cost-efficient control method for jellyfish blooms.