Observations on the occurrence of Allocreadium fasciatusi in Aplocheilus melastigma

Allocreadium fasciatusi is a common trematode occurring in the intestine of the fish Aplocheilus melastigma . The distribution of this fluke inside the fish host has been studied for a period of one year. The fluke occurred throughout the year, the incidence ranged from 20 to 88, and the number of parasites per infected host varied from 1 to 58. The fluke exhibited a seasonal cycle of occurrence with a peak both in incidence and intensity in the month of September. For the rest of the year the population remained constant and there was a balance between recruitment and loss from the trematode populations. The maturation cycle of A. fasciatusi also followed a seasonal pattern. Although the flukes were recruited in all the months, the peak invasion occurred in September. The large numbers of immature flukes received during this month became gravid by January. The availability of infective larvae was considered to be important in influencing the seasonal cycles.
The incidence and intensity of infection were found to be independent of the size of the fish but female fish were noted to be the more heavily infected.     

Population and seasonal distribution of Procamallanus daccai in Eutropiichthys vacha in Kaptai Lake, Chittagong, Bangladesh

The population and seasonal distribution of Procamallanus daccai (Nematoda: Procamallanidae) in Eutropiichthys vacha (Siluridae) from the Kaptai Lake were studied for a period of 20 months during 1986-1987. A total of 208 fish were necropsied and 5652 worms were recovered, of which 2392 were from 87 infected male fish and 3260 were from 89 infected female fish. Prevalence values varied from 50% to 95%. The intensity and abundance of nematodes fluctuated over the study period and are statistically significant (F=14.87, P<0.0001), and showed a seasonal preference for the summer period (F=33.39, P<0.05). The mean intensity was the highest in the smallest size group at 66.3+/-12.7 which gradually decreased to 4+/-1.89 in the largest size group. No significant differences were found between parasites from male and female hosts, except in the summer. Male parasites were less abundant in the population. Female worms were grouped into immature, maturing and gravid and all these stages were present throughout the year. The highest occurrence of both immature and gravid P. daccai was found during the months of February to April each year. Peak recruitment seems to occur during this period due to the presence of high quantities of immature worms.     

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.     

Field studies on the transmission of the human liver fluke, Opisthorchis viverrini, in northeast Thailand: population changes of the snail intermediate host

Field studies on the transmission of the human liver fluke, Opisthorchis viverrini, in northeast Thailand: population changes of the snail intermediate host. International Journal for Parasitology16: 545–552. A natural population of Bithynia siamensis goniomphalos, snail vector of the human liver fluke Opisthorchis viverrini was sampled for 3 years in a shallow reservoir in Khon Kaen Province, northeast Thailand. During the study period, the habitat experienced a 17-month drought followed by a surging flood. Snails suffered over 90% mortality during drying of the reservoir but died at an average rate of only 5% per month during aestivation. When water returned they migrated to new edge habitats, apparently on floating debris, and reproduced. Peaks in reproduction occurred following spring rains and after the fall monsoon flooding subsided. Normally, two generations are produced per year in seasonal habitats. The prevalence of O. viverrini infection averaged 0.11 % in adult snails over 8 mm in length; smaller snails were not infected.Control of opisthorchiasis through snail control does not appear practical because of the widespread distribution of the snails, their ability to survive in very unstable habitats, and for other reasons concerned with the existence of the fish host between snail and human hosts.     

The occurrence and life history of Asymphylodora kubanicum (Platyhelminthes: Digenea: Monorchidae) in the Worcester-Birmingham canal, with special reference to the feeding habits of the definitive host, Rutilus rutilus

Two hundred roach and over 400 molluscs were examined over a one year period to investigate the occurrence and life history of Asymphylodora kubanicum in the Worcester-Birmingham canal. Larval stages, infective to the fish definitive host, were present in molluscs throughout the year but did not show a seasonal fluctuation in numbers. Parasites in the intestine of the roach showed a marked annual cycle of occurrence and maturation: low winter infection levels preceded a dramatic increase in infection during the spring and summer. Maturation of the parasite population was rapid during the spring and summer and in late summer and early autumn the parasites laid their eggs and subsequently died. The death of parasites after egg-laying resulted in the low winter infection level during which time little recruitment occurred.
Roach became infected mainly in their third year when molluscs become a dominant component of their diet. Thereafter the older fishes (<2+) are all equally susceptible to infection, but the larger (older) fishes become more heavily infected because of the greater consumption of molluscs per fish. The sex of the fish made no difference to infection with the parasite.     

Seasonal studies of the biology of Achtheres percarum in perch, Perca fluviatilis, from four Finnish lakes over a 3-year period

Achtheres percarum infection on the gills of perch Perca fluviatilis was studied from four lakes in central Finland in monthly or bimonthly samples of fish during a 3-year period. The highest prevalence and intensity of infection (30%, 0.7 copepods/fish) were found in the oligotrophic, unpolluted Lake Peurunka and the lowest (6%, 0.1 copepods/fish) in the eutrophic and polluted Lake Vatia. According to hierarchical loglinear models the prevalence of A. percarum infection was related to the lake, but not to the year. However, when logit models were constructed such that two 'seasons' ('cold' and 'warm' periods) were included, it was apparent that the year also influenced the prevalence of A. percarum , but only during the 'warm' period of the year. Achtheres percarum had an age dependent relationship only in Lake Peurunka, where the infection increased with increasing age of the fish. Some developmental stages of A. percarum parasitizing the gills of perch are described. Data on the seasonal occurrence of A. percarum developmental stages are given and it is suggested that at least two generations are produced annually.     

The settlement, distribution and movements of O-group plaice Pleuronectes platessa (L.) in Filey Bay, Yorkshire

The pelagic larval stages and the demersal O-group stage of plaice were sampled in the immediate vicinity of Filey Bay, Yorkshire (54°12'N, 00°16'W), using a modified Gulf V high-speed plankton sampler and beam trawls. The distribution and movements of these fish were studied from the time of first settlement in May through the period of metamorphosis and the O-group stage. It was found that the larvae settled in water deeper than 5 m and moved into shallow water following metamorphosis. This established a typical distribution of larger fish in shallower water than the smaller fish. When the fish grew over 40 mm they moved out again into deeper water which leads to a reversal of the lengthdepth distribution. Further movements during the winter months and of the I-group fish were studied by tagging. It was found that emigration from the nursery ground did not occur until the I-group stage.     

Co-infection with Opisthorchis viverrini and Haplorchis taichui detected by human fecal examination in Chomtong district, Chiang Mai Province, Thailand

Diseases caused by the liver fluke, Opisthorchis viverrini and the minute intestinal fluke, Haplorchis taichui, are clinically important, especially in the Northeast and North regions of Thailand. It is often difficult to distinguish between these trematode species using morphological methods due to the similarity of their eggs and larval stages both in mixed and co-infections. A sensitive, accurate, and specific detection method of these flukes is required for an effective epidemiological control program. This study aimed to determine the prevalence of O. viverrini and H. taichui infections in human feces by using formalin-ether sedimentation and high annealing temperature random amplified polymorphic DNA (HAT-RAPD) PCR methods. Fecal specimens of people living along the Mae Ping River, Chomtong district were examined seasonally for trematode eggs using a compound microscope. Positive cases were analyzed in HAT-RAPD, DNA profiles were compared with adult stages to determine the actual species infected, and specific DNA markers of each fluke were also screened. Our results showed that out of 316 specimens, 62 were positive for fluke eggs which were pre-identified as O. viverrini and H. taichui. In addition, co-infection among these two fluke species was observed from only two specimens. The prevalence of H. taichui infections peaked in the hot-dry (19.62%), gradually decreased in the rainy (18.18%), and cool-dry seasons (14.54%), respectively. O. viverrini was found only in the hot-dry season (6.54%). For molecular studies, 5 arbitrary primers (Operon Technologies, USA) were individually performed in HAT-RAPD-PCR for the generation of polymorphic DNA profiles. The DNA profiles in all 62 positives cases were the same as those of the adult stage which confirmed our identifications. This study demonstrates the mixed infection of O. viverrini and H. taichui and confirms the extended distribution of O. viverrini in Northern Thailand.     

Species composition and seasonal variations of ichthyoplankton of the coastal zone of Vostok Bay (Peter the great bay,sea of Japan) collected at light stations

We summarize the results of a study of the taxonomic composition and seasonal variations of ichthyoplankton in Vostok Bay. Samples were collected during 2003–2008 at a stationary light station located on the mooring module of the experimental biological station Vostok (Institute of Marine Biology). Within the observation period, larval and juvenile fish of 67 species belonging to 11 orders and 30 families were found in 412 samples. The seasonal dynamics of species composition of ichthyoplankton were examined over the period from March to November. The number of species in the samples changed from 40–36 in April–May, respectively, to 6 species in October. The contribution of resident species and southern migrants to the ichthyoplankton samples was estimated. The light station sampling has proven to be most effective in studying the species diversity of the ichthyofauna in Vostok Bay. Using light station sampling, 18 fish species were found that were not recorded using other sampling techniques.     

Effects of the eye fluke Diplostomum spathaceum on the energetics and feeding of Arctic charr Salvelinus alpinus

In the present study, effects of the trematode eye fluke Diplostomum spathaceum infection and parasite‐induced cataract on energetic costs and feeding of hatchery‐bred one‐summer‐old Lake Saimaa Arctic charr Salvelinus alpinus were examined. The energetic effects (measured as oxygen uptake) of acute eye fluke infection on S. alpinus were negligible, but in the chronic infections mean oxygen consumption of infected fish was significantly higher than that of controls. Feeding capability of S. alpinus was studied in aquarium experiments, and uninfected healthy‐eyed fish reacted to zooplankton more rapidly and caught zooplankton with better success compared to individuals with cataracts in the same school. The results suggested that to compensate energetic costs and impaired feeding capability caused by eye fluke, cataract‐bearing fish spend more time foraging, which may result in increased predation risk.     

Distribution of common carp in a Spanish reservoir in relation to thermal loading from a nuclear power plant

Arrocampo Reservoir is used as a cooling basin for a nuclear power plant located in southern Europe. Its annual mean temperature is about 30 °C with maxims that achieved 41.5 °C near the hot water effluent. Common carp (Cyprinus carpio, Linnaeus 1758) is the dominant pelagic fish species in this reservoir. Hydroacoustic surveys were conducted bimonthly over 9 years to characterize common carp abundance and distribution in the reservoir on an annual and seasonal temporal scale. Mean fish density during the period was 0.029 fish m⁻³, varying from a maximum of 0.038 in 2003 to a minimum of 0.012 in 1998. There were no significant differences in the mean fish density among years. Each year, fish distribution showed significant seasonal variation. Carp were homogeneously distributed during autumn and spring; in winter carp occupied warmer outfall areas, whereas in summer, fish were distributed in the coldest area of the reservoir (dam area) but avoided the warm outfall area. These seasonal tendencies of carp distribution was repeated every years. Behavioural reaction appears to be particularly important in explain carp distribution in this reservoir.     

Reproductive biology of the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters

The reproductive activities of the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters were investigated from March 1996 to February 1998. Observations on the seasonal distribution of maturity stages and variations in seasonal fluctuations in the gonadosomatic index (GSI) confirmed recent findings that the spawning period begins in May. The species has a prolonged spawning period in the females extending from May to August, whereas the males mature in April and ripe specimens were encountered in monthly samples until September. The recruitment pattern confirmed the one breeding season. There are two spawning peaks, the first in May and the second in August. Variations in GSI relative to fish length indicated that females and males are most fecund at about 24.5–26.4 cm and 20.5–22.4 cm length classes, respectively. The males mature earlier than females, at a minimum size of 12.5–14.4 cm, while the females mature at 20.5–22.4 cm. The oocyte diameter‐frequency distribution suggests a serial rhythm of spawning. Fecundity ranged from 28 965 to 455 661 and correlated positively with: (a) standard length (P < 0.006); (b) ovary weight (P < 0.001); and (c) body weight (P < 0.001), and negatively with egg size (P < 0.003).     

Spatial and temporal patterns in fish assemblages of upper coastal plain streams, Mississippi, USA

We assessed spatial, seasonal, and annual variation in fish assemblages over 17 months in three small- to medium-sized, incised streams characteristic of northwestern Mississippi streams. We sampled 17 962 fish representing 52 species and compared assemblages within and among streams. Although annual and seasonal variability in assemblage structure was high, fish assemblages maintained characteristics unique to each stream. High variability in fish catch-per-unit-effort (CPUE) was exemplified in one site where total CPUE increased an order of magnitude from July 1993 to 1994. Species turnover and percent dissimilarity were often higher seasonally than annually, consistent with a period of change in spring to early summer and a return to similar species compositions between summers. Temporal variability was also high at the individual species level, and no species were classified as 'stable'. We found little evidence for correlation between changes in fish assemblage structure and measured habitat conditions. The fish characteristics fit the profile of 'colonizing assemblages', which probably resulted from both natural and anthropogenic causes. Flashy hydrographs , created in part by stream channelization and incision and watershed deforestation, may play a large role in structuring these fish assemblages. Extreme interannual variability in assemblages in the absence of detectable habitat change has important implications for the statistical power of fish monitoring programs designed to detect trends in fish assemblages over time.     

Ovarian aging in two species of long-lived rockfish, Sebastes aleutianus and S. alutus

Little is known about the ovary during aging in long-lived fish with respect to follicular stages and de novo oogenesis. We examined two species of rockfish, Sebastes aleutianus (rougheye rockfish) and Sebastes alutus (Pacific ocean perch). Fish were sampled offshore of British Columbia, age was estimated by otolith annuli, and the ovaries were examined histologically. In S. aleutianus, age up to 80 yr did not markedly alter the frequency distribution of oocytes, follicles, or their total numbers. Similarly, in a larger sample of S. alutus, the abundance of oocytes and follicles showed little age trend up through 77 yr. However, fish older than 50 yr lacked the largest and smallest oocyte size classes (40-60, >80 microm) and the smallest follicle size class (200-350 microm), which results from the later seasonal developmental state of these older fish. These data provide evidence that oogenesis continues at advanced ages in these two species, in contrast with long-held assumptions about mammals. These species represent an iteroparous extreme in the spectrum of life history strategies and merit investigation to determine the mechanisms for such an extended reproductive life span.     

Some observations on the food of the gwyniad Coregonus clupeoides pennantii Valenciennes of Llyn Tegid (Lake Bala), North Wales

The seasonal variations in the diet of adult gwyniad Coregonus clupeoides pennantii=C. lavaretus from Llyn Tegid, North Wales were studied. Stomachs were examined to determine fullness, volume and identity of contents.
A clear seasonal cycle in food intake was found. Feeding rates were low from January to April but increased during the summer (May-June) and remained at a high level until December. The period of low feeding intensity coincided with the time of spawning and the time of annulus formation of both scales and otoliths. The diet showed seasonal changes and two main periods were distinguished : December to July, when the fish fed mainly on bottom fauna, and August to November, when the diet included both bottom fauna and midwater and surface foods.
The gwyniad were shown to be opportunistic in feeding, the composition of the diet reflecting availability of food items rather than selective feeding on the part of the fish.     

Space-time organization of riverine fish communities in French Guiana

Synopsis A riverine fish assemblage in French Guiana was examined over several consecutive years. Fish distribution was highly structured on at least 3 different scales: between rivers, between the different zones of the rivers and between the different biotopes studied in sampling areas. A temporal organisation of fish communities was also found, superimposed on the spatial structure. The latter was due to the seasonal variations of the water level, and allowed temporary access to flooded areas. The different space-time factors of organisation of fish communities presented here are discussed in regard to their contribution to the maintenance of the observed high species diversity.     

Feeding habits and diet in two populations of spined loach, Cobitis taenia (L.)

SUMMARY. The feeding habits of Cobitis taenia were studied by means of monthly samples taken over a 2-year period, October 1972-October 1974, from two sites, one on the River Great Ouse at Newport Pagnell and the other at some neighbouring gravel pits. Dietury components, seasonal variation in these components, and seasonal and diurnal variation in feeding intensity were examined. The ecological niche of the food items and their size range are discussed, since both these factors appeared important in governing the micro-habitat of the fish.
The feeding activity followed a seasonal cycle with little or no feeding in the winter and a high level of feeding activity in mid-summer.
The diet showed a predominance of small food items, such as chydorids. copepods and rhizopods. These items varied in occurrence during the feeding period which appeared to be related to their own abundance, pointing to non-seleclive feeding by the fish. The small size and benthic habits of the food items, many of which are closely associated with surface layers of mud and weed, indicated a preference by Cobitis taenia (L.) for feeding in this type ot habitat and on this type of food, in contrast to the stone loach. Noemacheilus barbatulus (L.), which is believed to inhabit stony areas and take larger food items.     

Linking seasonal distribution patterns with prey availability in a central-place forager, the Steller sea lion

Aim We used a novel approach to infer foraging areas of a central‐place forager, the Steller sea lion (Eumetopias jubatus), by assessing changes in the temporal and spatial distribution patterns of sea lions at terrestrial sites. Specifically, our objectives were (1) to classify seasonal distribution patterns of Steller sea lions and (2) to determine to what extent the seasonal distribution of Steller sea lions is explained by seasonal concentrations of prey. Location Southeast Alaska, USA. Methods Steller sea lions of all age classes were counted monthly (2001–04) by aerial surveys at 28 terrestrial sites. Hierarchical cluster analysis and principal components analysis were used to classify seasonal distribution patterns of Steller sea lions at these terrestrial sites. We estimated the proportion of sea lions in the study area that were associated with each seasonal distribution pattern. Results Multivariate ordination techniques revealed four distinct seasonal distributional patterns. During December, 55% of the sea lions in the study area were found at Type 1 sites, located near over‐wintering herring aggregations. During May, 56% of sea lions were found at Type 2 sites, near aggregations of spring‐spawning forage fish. In July, 78% of sea lions were found at Type 3 sites, near summer migratory corridors of salmon. During September, 44% of sea lions were found at Type 4 sites, near autumn migratory corridors of salmon. Main conclusions Seasonal attendance patterns of sea lions were commonly associated with the seasonal availability of prey species near terrestrial sites and reflected seasonal foraging patterns of Steller sea lions in Southeast Alaska. A reasonable annual foraging strategy for Steller sea lions is to forage on herring (Clupea pallasii) aggregations in winter, spawning aggregations of forage fish in spring, salmon (Oncorhynchus spp.) in summer and autumn, and pollock (Theragra chalcogramma) and Pacific hake (Merluccius productus) throughout the year. The seasonal use of haulouts by sea lions and ultimately haulout‐specific foraging patterns of Steller sea lions depend in part upon seasonally available prey species in each region.     

Seasonal migrations and reproductive patterns in the lake sturgeon, Acipenser fulvescens, in the vicinity of hydroelectric stations in northern Ontario

This study was conducted in order to evaluate seasonal migratory behaviour and reproductive pattern of lake sturgeon in a confined region of the Mattagami River system in northern Ontario where river flow is regulated by hydroelectric works. Radio tracking and the systematic sampling of lake sturgeon using gill nets indicated that the distribution of fish throughout the study site varied on a seasonal basis. This distribution was related to the migration of individuals to potential spawning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River which is a tributary of the Mattagami River. There was a high proportion of fish (about 50%), within the size range of reproductively active fish, found in the vicinity of suitable spawning habitat during early May. Measurement of the gonadosomatic index (GSI) and plasma sex steroid hormone levels revealed a divergent pattern of reproductive development between the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17β-estradiol. In contrast, male lake sturgeon began testicular recrudescence within one month of spawning with the GSI reaching prespawning levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works has complex effects on sturgeon in the Mattagami system. The extensive migratory behaviour of lake sturgeon within the study area make it prone to impingement or entrainment whereas the altered river flow appears to enhance reproductive development. This revised version was published online in August 2006 with corrections to the Cover Date.     

Seasonality of recruitment and reproduction of Acanthocephalus tumescens (Acanthocephala) in fishes from Lake Moreno (Patagonia, Argentina)

The seasonality of recruitment and reproduction of Acanthocephalus tumescens at the component population level was investigated in Lake Moreno (Patagonia, Argentina). Seasonal samples of the principal fish host species were taken between spring 1999 and spring 2000. Prevalence, mean intensity, coefficient of dispersion, sex ratio, proportion of maturity stages of females, and percentages of the 2 sources of infection in the stomach of fishes were calculated. Overall prevalence, mean intensity, and coefficient of dispersion showed the same pattern of seasonal changes. The seasonal feeding patterns of fishes affect the occurrence of A. tumescens, producing 1 peak in spring and the other peak in autumn. The lower temperature in winter delay reproductive processes after the autumn period of recruitment.