Sensory cues for the gradual frequency fall responses of the gymnotiform electric fish, Rhamphichthys rostratus

The sensory cues for a less known form of frequency shifting behavior, gradual frequency falls, of electric organ discharges (EODs) in a pulse-type gymnotiform electric fish, Rhamphichthys rostratus, were identified. We found that the gradual frequency fall occurs independently of more commonly observed momentary phase shifting behavior, and is due to perturbation of sensory feedback of the fish's own EODs by EODs of neighboring fish. The following components were identified as essential features in the signal mixture of the fish's own and the neighbor's EOD pulses: (1) the neighbor's pulses must be placed within a few millisecond of the fish's own pulses, (2) the neighbor's pulses, presented singly at low frequencies (0.2–4 Hz), were sufficient, (3) the frequency of individual pulse presentation must be below 4 Hz, (4) amplitude modulation of the sensory feedback of the fish's own pulses induced by such insertions of the neighbor's pulses must contain a high frequency component: sinusoidal amplitude modulation of the fish's own EOD feedback at these low frequencies does not induce gradual frequency falls. Differential stimulation across body surfaces, which is required for the jamming avoidance response (JAR) of wave-type gymnotiform electric fish, was not necessary for this behavior. We propose a cascade of high-pass and low-pass frequency filters within the amplitude processing pathway in the central nervous system as the mechanism of the gradual frequency fall response.Abbreviations EOD electric organ discharge - f frequency of EOD or pacemaker command signal - JAR jamming avoidance response - S ₁ stimulus mimicking fish's own EOD - f ₁ frequency of S₁ - S ₂ stimulus mimicking neighbor's EOD - f ₂ frequency of S₂     

Sex‐specific distribution and diet of Platichthys flesus at the end of spawning in the northern Baltic Sea

This study examined the relationship of seascape structure, prey availability and sex on the post‐spawning distribution and diet of European flounder Platichthys flesus in the northern Baltic Sea. The objectives were to determine whether: (1) wave exposure and substratum affect abundance and distribution of P. flesus, (2) diet reflects the benthic prey composition and (3) sex affects the distribution or diet of P. flesus. The results showed that P. flesus was evenly spread in the archipelago with no correlation to wave exposure. The distribution was, however, sex specific; reproductive males dominated the exposed zone and mainly post‐reproductive females dominated the intermediate and sheltered zones. Platichthys flesus fed mainly on two bivalve prey species: blue mussels Mytilus edulis and Baltic tellins Macoma balthica. Hard substratum invertebrates dominated the diet in all habitats and apart from some typical soft substratum species, there was no clear link between fish feeding and the dominance structure of benthic prey. Diet was further sex specific, with females showing a broader range of diet than males. Results suggest that P. flesus is a specialist molluscivore found commonly and equally in soft‐ and hard‐substratum habitats throughout the archipelago area. Previous studies on P. flesus in the Baltic Sea have yielded inconsistent results regarding diet and it has commonly been believed that the distribution of Baltic Sea P. flesus is linked to sand and soft substrata. The present findings emphasize the importance of including the entire range of habitats when diet and regional species distributions are assessed.     

Ecological assessment of finfish as indicators of habitats in the Gulf of Nicoya,Costa Rica

Trawl samples of demersal fish populations within the Gulf of Nicoya, Costa Rica were conducted during February and July, 1979 and April, 1980 in an attempt to define basic abundance, diversity and distributional patterns. Seventeen day and three night samples produced 6 441 fishes of 107 species during the February cruise. Twenty day and two night samples produced 9 220 individuals of 131 species during the July cruise. Twenty day samples produced 14 151 individuals representing 125 species taken during the April cruise. A total of 214 species were collected during this study.The Gulf may be divided into three zones on the basis of the physical characteristics of the stations (water temperature, dissolved oxygen, salinity, depth and distance from the mouth of the Gulf). Few changes in the position of these zones occurred during the study period indicating a relatively stable estuarine configuration from a biological perspective.The Gulf of Nicoya area is under the influence of a wet and a dry season. No significant seasonal changes in the number, biomass, percent occurrence, diversity of partitioning by size class of fishes were observed.Two major types of fish distributional patterns were observed. Several species were ubiquitous and were found throughout the Gulf in varying abundances. Other species were restricted to either the upper or lower Gulf. Dominant groups in the upper Gulf include the sciaenids, sea catfishes (Ariidae) and flatfishes (Soleidae, Cynoglossidae andSyacium ovale). These fishes tend to inhabit the warmer, shallower, less saline waters of the upper Gulf. Flounders (bothidae), gobies (Bollmannia spp.), morays and congers (Hildebrandia nitens, Priodonophus equatorialis andMuraenesox coniceps) and several other species dominated the deeper, cooler, more saline lower Gulf.     

Habitat use of the European mudminnow Umbra krameri and association with other fish species in a disconnected Danube side arm

Fish assemblages along the longitudinal course of an old, disconnected and modified side arm of the Danube floodplain downstream of Vienna, Austria, as well as habitat structure, hydro‐morphological and hydro‐chemical factors, were investigated in order to analyse the key environmental determinants of the European mudminnow Umbra krameri. Generally, U. krameri was the most abundant species in the system. It occurred in disconnected ditches, ponds and pools with dense reed belts and comparatively low nutrient content, indicating its natural association with marsh habitats. At infrequently disturbed sites it was associated with a small group of stagnophilious and highly specialized species with adaptations to strong oxygen fluctuations. At frequently flooded sites, the species was absent or occurred in low abundances, indicating its adaptation to water bodies in older successional stages and its low competitive power in permanently connected floodplain habitats.     

Fish cell lines: Two new cell lines derived from explants of trunk musculature ofCynoscion arenarius

Summary Two cell lines were established from explants of trunk musculature of healthy, males sand seatrout,Cynoscion arenarius. One of the lines, designated CyA-1, has been carried through 150 subcultures during 6 yr. The other, designated CyA-2, has been carried through 100 subcultures during 2 yr. Both lines grow well in L15 medium adjusted to 0.150M NaCl and supplemented with 10% fetal bovine serum. Optimal growth occurs at temperatures between 24 and 30°C. The species of origin of both lines was confirmed by a cytotoxic antibody dye exclusion test. The karyotype of CyA-1 has not yet stabilized, showing a modal chromosome number of 120 at Passage 9, 89 at Passage 63, and 79 at Passage 100. The karyotype of CyA-2 is rather stable, with a modal chromosome number of 47 at Passage 1 and 49 at Passage 100. Chromosome morphology of CyA-2 is homogeneous (small, acrocentric), whereas the chromosomes of CyA-1 show considerable size variation (with small chromosomes possibly formed from fragmentation of original structures). Both lines were found to be free of bacterial or fungal contamination. Both lines supported replication of lymphocystis virus strains isolated fromBairdiella chrysura (the silver perch) and fromMicropogon undulatus (the Atlantic croaker) but were refractory to 11 other viruses (4 from fish, 1 from amphibians, and 6 from mammals). This study was supported in part by the National Oceanographic and Atmospheric Administration, Office of Sea Grant No. 04-3-158-58.     

A mass mortality of fishes caused by receding water levels in the vegetated littoral zone of the West Kleinemonde Estuary,South Africa

On 15 November 2017 the mouth of the West Kleinemonde Estuary breached following heavy catchment rains and increased river flow. The water level in the estuary following mouth opening decreased by 1.65 m within 24 h, resulting in an almost complete draining of the littoral zone where large beds of the aquatic macrophyte Ruppia cirrhosa and mats of the associated filamentous algae were present. As the water depth within the plant beds decreased, the macrophytes, together with the algal filaments, created an increasingly dense mat, trapping fish that were resident, foraging or passing through the littoral zone. By 16 November 2017 large numbers of fishes belonging to at least 20 species were trapped in pools and depressions within the littoral, as well as within the R. cirrhosa beds and filamentous algal mats in the lower reaches of this system. Other affected taxa included crustaceans, especially isopods, and large numbers of small bivalves attached to macrophyte vegetation. Beneficiaries of the fish kill, in terms of unexpected food availability, included a variety of piscivorous bird species and the Cape clawless otter Aonyx capensis. This is the first documented account of a diverse species fish kill associated with estuary mouth breaching.     

Five new records of Luvarus imperialis (Acanthuroidei: Luvaridae) in the south‐west Atlantic Ocean

Five new records of louvars Luvarus imperialis are documented for the south‐west Atlantic Ocean, extending its distribution range in this ocean. The presence of one ripe specimen, associated with the previous records of larvae and juveniles, suggests that L. imperialis spawn in this region. The possible association of juveniles with shoals of skipjack tuna Katsuwonus pelamis is discussed.     

Effect of fish length and nutritional condition on the fecundity of distressed Atlantic cod Gadus morhua from the Baltic Sea

The disappearance of larger individuals and the decrease in individual body condition suffered by Atlantic cod Gadus morhua in the eastern Baltic during the past two decades can be expected to affect the stock reproductive output. To investigate this, female G. morhua were collected during the spawning and pre‐spawning period in 2015?2016. The current individual potential fecundity (F_P) of eastern Baltic G. morhua was estimated and analysed in relation to total length (L_T) and indices of nutritional status such as body condition (K) and hepato‐somatic index (I_H) using generalized linear models. In addition, the current prevalence of atresia and its potential relation to K were investigated. Moreover, a calibration curve to estimate F_P from oocyte diameter, based on the autodiametric oocyte counting method, was established for the first time for eastern Baltic G. morhua and can be used for future fecundity studies on this stock. The results showed that F_P was mainly positively related to fish length, but K and I_H also contributed significantly to the variation in F_P. The model predicted that fish with K = 1·2 have a F_P 51% higher than fish of the same L_T with K = 0·8. The prevalence of fecundity regulation by atresia was 5·8%, but it was found only in fish in the pre‐spawning maturity stage and with low K. Temporal changes in biological features such as the length composition and individual body condition of eastern Baltic G. morhua, should be accounted for when estimating stock reproductive potential.     

Fish parasitism in a new impoundment and differences upstream and downstream

The parasitic fish fauna in Guelph Lake, a four-year old impoundment, were compared with those in upstream and downstream localities. The lacustrine assemblage of the young mesotrophic to eutrophic impoundment was dominated by the cestodes, Ligula intestinalis and Proteocephalus ambloplites, and the nematode, Philometra sp. The acanthocephalan, Neoechinorhynchus saginatus, and the nematode, Rhabdacona cascadilla dominated the rheophilous assemblage of fish parasites, but the prevalence rate and intensity of R. cascadilla was significantly reduced downstream.     

长江安庆段江豚主要栖息地鱼类群落结构

长江皖河交汇处(皖河口)是安庆江段江豚主要的栖息地之一。为了解江豚主要栖息地鱼类群落结构,于2013年9月—2014年8月对皖河口及其附近4个断面逐月进行了鱼类调查。研究结果表明,共采集鱼类35种,与历史资料相比,鱼类物种多样性已经严重下降,并且小型化趋势明显。5个断面当中,皖河口鱼类种数最多,为27种,且以中上层鱼类餐和油餐为主要优势种;其余4个断面分别为16、20、19和14种,且多数断面以底层鱼类黄颡鱼和长须黄颡鱼为主要优势种。方差分析结果表明,皖河口渔获物的总数量和总重量与其他断面无显著差异,但总种数却显著高于断面1和5。对中上层、中下层和底层鱼类的进一步分析发现,5个断面的显著差异仅存在于中上层鱼类,且皖河口中上层渔获物的数量和重量均显著高于其他断面。由此推断,江豚选择皖河口作为主要栖息地可能主要由于其更加丰富的中上层鱼类资源。研究结果不仅有助于了解鱼类资源的变化,还对江豚的原地和迁地保护具有重要意义。     

Eco-morphological patterns of the sagitta of Antarctic fish

Morphology and morphometry of the sagittae otolith were studied in pelagic and mesopelagic fish. The shape, margins and rostrum of four groups of otoliths from several species were analyzed: group 1 (pelagic fish associated with the under ice cover N = 42), group 2 (pelagic fish associated with water offshore N = 9), group 3 (mesopelagic fish associated with extensive vertical migration N = 57) and group 4 (mesopelagic fish associated with short vertical migration N = 54). E (maximum width of the sagitta /maximum length of the sagitta %), R (rostrum length (RL)/maximum length of the sagitta %) and S (sulcus area (SS)/otolith area (OS) %) indexes were calculated for each species. Sagittae of pelagic groups (1 and 2) showed the smallest sagitta dimensions in relation to the total length of the fish, in this group the sagitta shape is variable. Sagittae of mesopelagic fish (groups 3 and 4) showed variable shape and edges. The shape in group 4 was polygonal and these species have more width than length. Statistical analysis showed significant differences in the E, R and S indexes. These results were compared with other 19 species, belonging to six families, taken from a publisher-edited literature. E, R and S-values could be used to characterize the sagittae of the Antarctic fish and could be considered as a useful tool for fish ecology studies.     

Timing and size of blooms of the ctenophore Mnemiopsis leidyi in relation to temperature in Narragansett Bay, RI

The ctenophore Mnemiopsis leidyi is at the northern extreme of its geographic range in Narragansett Bay, an estuary on the northeast coast of the United States. Blooms have typically been observed in late summer and fall according to records from 1950 to 1979. We document an expansion of the seasonal range of this important planktonic predator to include springtime blooms during the 1980s and 1990s. This shift to an earlier seasonal maximum is associated with increasing water temperature in Narragansett Bay. Temperatures in spring have risen, on average, 2 °C from 1950 to 1999 with warm years being associated with the positive phase of the North Atlantic Oscillation. During 1999, M. leidyi appeared earlier in spring and was more abundant than during any previous year for which records are available. Changes in the seasonal pattern and abundance of this predator are likely to have important effects on planktonic ecosystem dynamics of Narragansett Bay. These include reduction of zooplankton abundance in spring followed by increases in size and frequency of summer phytoplankton blooms. Earlier blooms of M. leidyi may also reduce survival of eggs and larvae of fish because, as in 1999, they coincide with the period of peak spawning.     

Arms as areas for larval development of migratory fish species in a Neotropical reservoir and the influence of rainfall over abundances

The aim of the present study was to verify the use of the arms of the Itaipu Reservoir as areas of initial development for migratory fish species and to assess the relationship between rainfall and the spawning of migratory fish. Accordingly, fish larvae were collected from five arms of the reservoir from 2009 to 2016 using 0.5 mm plankton nets. Density was standardized as the number of larvae per 10 m³ filtered water, and the captured larval and juvenile specimens were identified at the lowest-possible taxonomic level. The larvae were also classified according to the degree of development and notochord flexion stage: larval vitelline, pre-flexion, flexion and post-flexion. To evaluate the distribution of larval abundance and the developmental stage along the longitudinal gradients of the arms, the data were evaluated using a set of nested linear models, following the AIC and Bayesian information criteria. In addition, an analysis of covariance was performed to investigate the influence of rainfall on the larval abundance of migratory species. During sampling, several species of economic and conservation interest such as Salminus brasiliensis and Pseudoplatystoma corruscans were collected. The larvae of the migratory fish taxa were captured from all sampled arms, which indicate them as areas of initial development. Nevertheless, it was observed that larval density increases from fluvial towards lacustrine zones inside the arms. Also, the present study verified that species, even in lentic environments, respond positively to rainfall stimuli in a manner similar to that exhibited by conspecifics in lotic environments. Such results reinforce the necessity of the protection of arms aiming at the conservation of this main group of species impaired by the construction of dams.     

Purification and characterization of interferon-like antiviral protein derived from flatfish (Paralichthys olivaceus) lymphocytes immortalized by oncogenes

Flatfish leukocytes were transfected with the expression plasmids of the v-myc, c-myc, c-fos, v-myb and c-Ha-ras oncogenes. Only cotransfection of c-Ha-ras with c-myc or c-fos resulted in complete immortalization of the cells. Interferon-like anti-viral protein was found in the cultured medium of the immortalized lymphocytes. The protein was purified by DEAE-Toyopearl 650 M ion exchange chromatography and WGA agarose affinity chromatography. The protein was a glycoprotein of about 16 kDa. The antiviral activity of the protein was trypsin-sensitive and was fairly stable at pH values from 4 to 8. The protein retained about 60% of the activity even at 60°C and showed a broad antiviral activity for various fish cells and viruses.     

Antigen profiles of the fish pathogen Moritella viscosa and protection in fish

Aims: Moritella viscosa is a Gram‐negative bacterium that causes winter ulcer disease in salmonid fish cultured in sea water below 8°C. The aim of this study was to study the antigen profiles of these bacteria and to reveal the protection which the antigens induce in fish. Methods and Results: Lipooligosaccharides (LOS) and an approximately 17–19 kDa outer membrane antigen were shown to be the major specific antigens of M. viscosa. The size of the wall antigen differed between strain groups and even between strains reacting positively in the same sera. Four different serotypes of M. viscosa were determined by producing polyclonal sera. Western blot analysis revealed that sera from vaccinated fish groups that had good or fair protection reacted against the LOS and the 17/19 kDa antigen, while no antibody response was observed with sera from groups that showed no efficacy. Conclusions: The study provides evidence that LOS and an approximately 17–19 kDa outer membrane antigen are the major specific protective antigens of M. viscosa, and that the M. viscosa species consists of many different serotypes. Significance and Impact of the Study: The results are important for the production of vaccines against winter ulcers and should also lead to better methods of verifying the bacteria and monitoring winter ulcers.     

A comparison of passage efficiency for native and exotic fish species over an artificial baffled ramp

This study used an experimental approach to compare the passage success of native and exotic fish species from the temperate Southern Hemisphere over an artificial baffled fish ramp designed for overcoming low-head (≤1.0 m) fish migration barriers. Passage efficiency was, on average, lower for the exotic species [koi carp (Cyprinus carpio), rudd (Scardinius erythrophthalmus) and rainbow trout (Oncorhynchus mykiss)] compared to the native species [inanga (Galaxias maculatus), redfin bully (Gobiomorphus huttoni) and common bully (Gobiomorphus cotidianus)]. Nonetheless, there was considerable variation between individual species, with rainbow trout outperforming common bully and juvenile inanga, but koi carp and rudd failing to pass any of the ramps. The differences in predicted probability of passage success between the native and exotic fish species in this study were sufficient in some cases to indicate the potential for the baffled fish ramps to operate as a selective migration barrier. Nonetheless, further testing is required to validate these results across a broader range of conditions before deployment.     

Patterns of Local Distribution of Labroides Dimidiatus in French Polynesian Atolls

Cleaning behaviour by fishes has been described to be either facultative or specialised. If being specialised in cleaning is more advantageous than to be a facultative cleaner, cleaner fishes would prefer to settle on reefs were ecological conditions promote specialisation. To test this hypothesis, we looked at the influence of physical and ecological factors on cleaner wrasse abundance, studying variations in L. dimidiatus density between 10 atolls of French Polynesia. We used a multiple regression method based on permutations of distance matrices. Our study reveals that L. dimidiatus are significantly more numerous at sites where ecological factors, such as the species richness of the fish community, may promote their cleaning activity. Moreover, they were significantly more abundant in atolls presenting a large number of sedentary fish species, few predators and few fishes living in large groups. Finally, physical factors, such as the distance between atolls, the lagoon surface, the mean percentage of hard substrate, the mean current index, and the mean depth, play a minor role in the occurrence of L. dimidiatus.     

Feeding and locomotor rhythm of the ornamental cichlid fish Amatitlania sp. in different social groups

The aim of this study was to evaluate the feeding activity and the rhythm of daily locomotor activity of the convict cichlid (Amatitlania sp.) kept in different social groups under a self-feeding system. A total of 120 animals was distributed among six repetitions of four social groups, as follows: group 1 with one male and one female per tank; group 2 with three males and three females per tank; group 3 with six males per tank; and group 4 with six females per tank. Feeding activity (FA) and locomotor activity (LA) were evaluated using photoelectric presence-sensors connected to automatic feeders. The fish were fed a commercial extruded diet (46% crude protein and 3600 kcal kg⁻¹ of digestible energy). Animal growth was evaluated for all groups. After 30 days of experimentation, the fish stabilized their demands by adjusting their consumption. Amatitlania sp. showed predominantly diurnal FA and LA. All groups showed a peak of activity when the light was turned on and when it was turned off. In summary, FA and LA of Amatitlania sp. are predominantly diurnal and independent of social group. Pairs and groups of males and females together consume less food in relation to groups of one sex or the other due to reproductive behaviour. On the other hand, groups of only males or females consume more food because they lack reproductive stimuli and thus prioritize growth. These results may support good feeding management practices for this ornamental cichlid. Studies relating feeding behaviour with different social groups are of great importance for determining effective feeding strategies for this species in captivity. Thus, such a study assists in a more efficient production of Amatitlania sp.     

The fish community of the Loosdrecht Lakes and the perspective for biomanipulation

In a two-year-study, the fish community of the Loosdrecht Lakes area was characterized with regard to the professional fishery and the forage base. The lakes are shallow (mean depth 2 m) and eutrophic to hypertrophic. The bream,Abramis brama, dominates the fish biomass. The pikeperch,Stizostedion lucioperca, is the main predator.Bream up to 30 cm have a slow growth rate and are in a bad condition. A faster growth rate and a better condition are shown by bream of 30 cm and more. The small bream feeds on chironomid larvae, benthic cladocerans and zooplankton. The better condition of bream over 30 cm is explained by the more efficient feeding of larger bream onChironomus plumosus larvae. Pikeperch show a fast growth rate and a good condition. Recruitment is limited by the low densities of smelt,Osmerus eperlanus, leaving cannibalism as the most important way for the 0+ pikeperch to become piscivorous and to manifest a fast growth.The impact of the professional gillnet fishery on bream and pikeperch is small because the mesh sizes in use are as large as 75–100 mm bar mesh.The planktivorous 0+ pikeperch consumes mainly the carnivorous zooplanktersLeptodora kindtii and cyclopoids. The zooplankton community lacks large herbivorous species likeDaphnia hyalina, capable of consuming bluegreens. A possible experiment in biomanipulation with a view to find out whether the development ofD.hyalina is depressed by the small planktivorous cyprinids, is predator enhancement with the aid of a stocking programme for indoor-raised 0+ pikeperch in early summer.     

The inshore marine fishes of the Vestfold Hills region,Antarctica

Thirteen species of fish have so far been caught in the inshore waters around the Vestfold Hills, including the Rauer Islands, in depths down to approximately 100 m. Species caught depend markedly on the type of fishing gear used, but three species are clearly dominant numerically. Pagothenia bernacchii is most abundant in the shallower (< 20 m deep) weedy and rocky habitats, while Chionodraco hamatus is dominant in the deeper (> 20 m deep) nearshore troughs and further offshore. Pagothenia borchgrevinki occupies the specialized habitat associated with sea ice and close-inshore areas, including fjords and Burton Lake.The species list from the Vestfold Hills area is similar to lists from comparable locations in East Antarctica except for the major difference that C. hamatus has not yet been recorded from such shallow waters at the other locations, while P. bernacchii and P. hansoni are much more abundant in water deeper than 20 m at those sites than at Davis.