Cystidicola farionis as a swimbladder parasite of the whitefish in the Bothnian Bay

Material comprising 3167 specimens of the parasite Cystidicola farionis was assembled from 1741 individuals of the sea-spawning whitefish, Coregonus nasus in the shallow northeastern and deeper central areas of the Bothnian Bay. Occasional parasites were found in the immature fish (≦ 175 mm), but infection increased in the two larger classes as the fish aged, reaching 27% in the northeastern area, and as much as 67% in the southern area. This difference is explained partly by the more frequent feeding on Pontoporeia affinis , the intermediate host for the parasite, the deeper waters extending nearer the coast in the majority of the central and southern Bothnian Bay. The increased intensity of infection with age does not vary significantly between the areas studied. No clear seasonal fluctuations in the prevalence or intensity of infection could be found.     

Density and distribution of the ringed seal in the Bothnian Bay

A modified strip census of basking ringed seals in the Bothnian Bay was carried out during the last week of April and the first week of May 1988. Of the total ice covered area, 23174 km², 3236 km² (14%) was covered by the transects. The mean density in the area was 0.101 ringed seals km^-2, with substantial regional and local variation. Highest densities were found in the compact drift ice area. The estimated total population of ringed seals on the ice was 2093 in the Bothnian Bay proper and 248 in the North Quark. The 95% confidence limits of the estimates are ±24%.     

Vegetation development on the outer islands of the Bothnian Bay

This paper summarizes succession studies on the outer islands of the Bothnian Bay (Finland). The study area is characterized by consistent and relatively rapid uplift (vertical rise on average 75 cm per century). The spatial and temporal succession has been deduced from the sequence of the littoral and epilittoral vegetation as well as from the historical records of the island development.Four types of successional series are distinguished. The relationships between substrate type (boulder, gravel, sand and clay-silt shores) and 25 typical plant communities are outlined and treated as successional sequences.     

Spectrofluorimetric determination of biogenic amines (serotonin, dopamine) in Metechinorhynchus salmonis (Acanthocephala)

Identification of serotonin and dopamine in M. salmonis was conducted by means of some fluorometric methods. The presence of negligible amount of a serotonin-like component and substance close in its spectral characteristics to dopamine was shown.     

Vertebrate diets derived from trophically transmitted fish parasites in the Bothnian Bay

Parasites that are transmitted through predator–prey interactions may be used as indicators of trophic relationships between organisms. Yet, they are rarely used as such in the construction of topological (predator–prey) food webs. We constructed food webs of vertebrate trophic interactions using observed diet alone, trophically transmitted parasites alone, and the combination of the two based on data from 31 species of fish from the Bothnian Bay, Finland. The fish food web contained 530 links derived from observed diet, 724 links inferred from parasitism, and 1,058 links calculated from a combination of both stomach contents and parasites. This sub-web constructed from stomach contents had a mean of 17.1 links per fish species, while that using parasites had 23.4 links per fish. Combining the two diet indicators yielded 34.1 links per fish species, illustrating the complementarity of the two methods. Mean number of prey species per fish species was 12.5 using observed diet items, 15.8 using parasites, and 24.5 using both measures together. Mean number of predators per fish species was 7.4 using observed diet, 11.7 using parasites and 15.0 using both. A positive correlation was found between the mean number of parasites and the number of prey taxa in the diet among the fishes. Omnivorous fish had the highest diversity of both parasite species and prey items, while benthophagous fish had among the lowest. Mean total abundance and mean total prevalence of parasites correlated positively with fish size, with piscivores being the largest with the highest abundance and prevalence, while planktivores and benthivores had the lowest. Trophically transmitted parasites may be used to help construct vertebrate sub-webs and derive information about food web processes. Parasites alone provided equivalent if not more information than observed diet. However, resolution is improved by using parasites and observed diet together.     

Migratory behaviour of adult cisco, Coregonus albula L., in the Bothnian Bay

The population of adult cisco in the Bothnian Bay consists of a number of spawning populations. Each one of these returns to the same inshore area for spawning every autumn. In the summer these populations are mixed and occur mainly offshore. These are the main conclusions of an experiment in which cisco were marked with Carlin-type tags. The cisco were caught mainly in fyke nets both in the summer and in the autumn and released after tagging in the area where they had been caught. Fish tagged in the autumn and recaptured in the autumn one or more years later showed a strong affinity to the point of release, while fish from the same group recaptured in the summer had migrated far from the release site. The distribution of cisco that were tagged in the summer and caught in the autumn showed no correlation with the release site.     

Further observations on flagellates within sea ice in northern Bothnian Bay, the Baltic Sea

To improve our knowledge of flagellates inhabiting the Baltic Sea ice and water column during the winter, material was obtained from northern Bothnian Bay in March/April 1995. Light microscopical observations on live and fixed material and further transmission electron microscopy of whole mounts revealed 47 nanoflagellate taxa. In addition, detached scales of eight taxa were encountered. It is now evident that nearly all nanoflagellate classes are present within Bothnian Bay sea ice. The most common groups were cryptomonads, dinoflagellates, chrysophytes, prasinophytes, choanoflagellates and heterotrophic flagellates of unknown systematic position (Protista incertae sedis). Most flagellates in Baltic Sea ice biota apparently thrive in both the water column and the sea ice, while some, e.g. Paraphysomonas spp. (Chrysophyceae), heterotrophic euglenids, volvocalean chlorophytes, and some taxa of uncertain systematic affinity, are more frequently found within the sea ice. Received: 9 February 1997 / Accepted: 23 September 1997     

Shade-adapted Algae beneath Ice and Snow in the Northern Bothnian Sea

The winter-spring phytoplankton flora in the coastal waters of the northern Bothnian Sea consists mainly of marine cold water species even adapted to low light. These dinoflagellates and diatoms seem to be selectively promoted by the seven months of low light and water temperature. They are able to grow during this period of subsaturated light and have their abundance maxima around ice-break. Solar radiation measured under ice and snow cover was in the same order of magnitude as the compensation points of some of the species. In summer, these algae species vanish from the water, and surely survive in the form of inactive life stages.     

Seasonal changes in condition indices in adult mature and non-maturing burbot, Lota lota (L.), in the north-eastern Bothnian Bay, northern Finland

The population structure and seasonal changes in condition factors of the burbot in a shallow coastal region of the north-eastern Bothnian Bay are described. The significance of the so-called rest years is examined by comparing condition indices in immature or sterile and mature burbot. The somatic condition index ( K ₂), liver index ( K ₁), intestine index ( K ₁) and gonad index ( K_g ) are determined monthly in terms of organ weight in relation to body length. Approximately 30% of the whole catch of 1052 burbot were non-maturing but were 40 cm or more in length. K ₂, K ₁ and K ₁ were lowest in the autumn, when the first sign of gonad recrudescence was observed in mature burbot. The non-maturing burbot were never in poorer condition than mature ones. As mature and non-maturing burbot dissipated their energy stores during the warmest period of the summer, it is concluded that burbot spending a rest year do not accumulate and store energy reserves over the summer for the next year, and that such rest years, if they exist, do not occur for nutritional reasons.     

Feeding interactions and diet of carnivorous fishes in the Shelikhov Bay of the Sea of Okhotsk

The food spectra, trophic statuses, and feeding interrelations of three most abundant benthic carnivorous fish species inhabiting the Shelikhov Bay—the Pacific cod Gadus macrocephalus, the great sculpin Myoxocephalus polyacanthocephalus, and the Okhotsk sculpin M. ochotensis—are considered based on materials collected during the complex survey of the RV Professor Kaganovsky of the TINRO-Center, in September 2004. It was found that these species were facultative predators with wide food spectra. The significance of prey objects in the diet of the Okhotsk sculpin was as follows: crustaceans, fish, and mollusks. Great sculpin and Pacific cod preyed mostly on fish, then on crustaceans, and mollusks. Pacific cod ate equal proportions of fish and decapods. All the species had age-related variability of diet. The potential competition of great sculpin and Okhotsk sculpin for food was mitigated by the difference in the depths of their ranges, as well as by morphological (body size) and behavioral peculiarities in the areas where their habitats overlapped, and in microecosystems. The most probable competition was among Pacific cod 30–60 cm long and Okhotsk sculpin 20–50 cm in length, as well as among cod and great sculpins of all sizes.     

Denitrification and N2O effluxes in the Bothnian Bay (northern Baltic Sea) river sediments as affected by temperature under different oxygen concentrations

Denitrification rates and nitrous oxide (N₂O) effluxes were measured at different temperatures and for different oxygen concentrations in the sediments of a eutrophied river entering the Bothnian Bay. The experiments were made in a laboratory microcosm with intact sediment samples. ¹⁵N-labelling was used to measure denitrification rates (Dw). The rates were measured at four temperatures (5, 10, 15 and 20°C) and with three oxygen inputs (<0.2, 5, and 10 mg O₂ l⁻¹). The temperature response was highly affected by oxygen concentration. At higher O₂ concentrations (5 and 10 mg O₂ l⁻¹) a saturation over 10°C was observed, whereas the anoxic treatment (<0.2 mg O₂ l⁻¹) showed an exponential increase in the temperature interval with a Q ₁₀ value of 3.1. The result is described with a combined statistical model. In contrast with overall denitrification, the N₂O effluxes from sediments decreased with increasing temperature. The N₂O effluxes had a lower response to oxygen than denitrification rates. The N₂O/N₂ ratio was always below 0.02. Increased temperatures in the future could enhance denitrification rates in boreal river sediments but would not increase the amount of N₂O produced.     

Genetics of whitefish and vendace in England and Wales

Proportion of loci polymorphic ( P ) and mean heterozygosity per locus ( H _exp) were P = 0.130 and H _exp= 0.096 for C. albula from the English Lake District and P = 0.217 and H _exp= 0.046 for C. lavaretus from the English Lake District and Llyn Tegid, Wales in 1991–2. Significant deviation from the Hardy-Weinberg model was observed at the superoxide dismutase ( sSOD* ) locus in C. albula from Bassenthwaite Lake. This could have been due to chance, to the Wahlund effect or to selection. Genetic distances between the two species were consistent with their taxonomy and genetic differentiation was much greater for the C. lavaretus populations than for the two geographically close C. albula stocks. Llyn Tegid C. lavaretus showed unique alleles at two loci and conservation of fish in this lake is therefore of great importance. Red Tarn C. lavaretus differed most from other Lake District populations probably due to founder effects from early stocking events and/or from selection due to the high altitude of this lake.     

MHC-linked susceptibility to a bacterial infection, but no MHC-linked cryptic female choice in whitefish

Non-random gamete fusion is one of several potential cryptic female choice mechanisms that have been postulated and that may enhance the survival probability of the offspring. Previous studies have found that gamete fusion in mice is influenced by genes of the major histocompatibility complex (MHC) region. Here we test (i) whether there is MHC-dependent gamete fusion in whitefish (Coregonus sp.) and (ii) whether there is a link between the MHC and embryo susceptibility to an infection by the bacterium Pseudomonas fuorescens. We experimentally bred whitefish and reared sibships in several batches that either experienced or did not experience strong selection by P. fluorescens. We then determined the MHC class II B1 genotype of 1016 surviving larvae of several full sibships. We found no evidence for MHC-linked gamete fusion. However, in one of seven sibships we found a strong connection between the MHC class II genotype and embryo susceptibility to P. fluorescens. This connection was still significant after correcting for multiple testing. Hence, the MHC class II genotype can considerably influence embryo survival in whitefish, but gamete fusion seems to be random with respect to the MHC.     

Contribution of Ciliated Microprotozoans and Dinoflagellates to the diet of three Copepod species in the Bay of Biscay

Predation of three calanoid copepods (Calanus helgolandicus, Temora longicornis and Centropages chierchiae) on phytoplankton, dinoflagellates and ciliates was estimated in the Gironde estuarine plume (Bay of Biscay) during winter by means of in situ incubations. Both phytoplankton and ciliates were part of the diet of those three species, while only Centropages chierchiae also included a significant portion of dinoflagellates in its diet. The clearance rates of Calanus helgolandicus for ciliates and phytoplankton reached 2.8 and 4.0 ml copepod^–1 h^–1, respectively, those of Temora longicornis were 3.2 and 1.8 ml copepod^–1 h^–1, and those of Centropages chierchiae were 4.3 and 0.8 ml copepod^–1 h^–1.Neither Calanus helgolandicus nor Temora longicornis selected dinoflagellates, given the low clearance rates measured for this prey category (0.05 and 0.03 ml copepod^–1 h^–1, respectively). By contrast, Centropages chierchiae included dinoflagellates in its diet, with a clearance rate of 4.9 ml copepod^–1 h^–1. Within a given prey category (ciliates or dinoflagellates), all three copepods selected larger prey types (>40 m) over smaller ones (40 m). This implies a better detection and capture of larger motile prey compared to small ones. The results are discussed with regard to the omnivorous feeding behavior of these copepods observed here, during a late winter phytoplankton bloom.     

Experimental infection of coho salmon Oncorhynchus kisutch by exposure of skin, gills and intestine with Piscirickettsia salmonis

Piscirickettsiosis pathogenesis was examined using some tissues as entry portals of Piscirickettsia salmonis in coho salmon. Juvenile fish, weighing approximately 8.4 g, were used in this trial. Inocula were prepared using the strain SLGO-95 of P. salmonis. The micro-organism was cultured in the CHSE-214 cell line as described by Fryer et al. (1990) and doses containing 10(4.7) and 10(3.7) TCID50 were prepared. Each dose was used to infect the fish via skin, gills and intestine. Skin and gills were exposed by calibrated drops, and the intestine by an intubation through the anal opening. Some fish were injected intraperitoneally with the same P. salmonis doses, as positive virulence controls. Sham-inoculated fish for each of the tested routes were also included as negative controls. Piscirickettsiosis was experimentally reproduced with all the inoculation methods. Cumulative mortalities and survival analyses showed that the most effective entry portal was skin followed by intestinal intubation and finally by gill infection.