Survival, growth and feeding of vendace, Coregonus albula (L.), larvae in net enclosures

Vendace, Coregonus albula (L.), larvae reared in net enclosures anchored in the littoral zone of Lake Ylä-Enonvesi, eastern Finland, were observed for a period of 44 days in order to determine the effects of density on mortality, growth and feeding of the larvae. The ratio of newly-hatched fish to their food was regulated by controlling the number of fish stocked into the enclosures. Prey animals were expected to move freely in and out of the enclosures. The effect of nylon mesh (500 μm) on the penetration of zooplankters into the enclosures was negligible. The influence of possible starvation was determined by analysing the growth of the larvae, their Fulton condition factor, the instantaneous amount of food ingested, and the food composition in their guts. All these indicators were inversely correlated with larval density. Vendace larvae were found to be resistant to mortality from direct starvation. At all densities the survival rate was over 60%. At the time of complete yolk absorption, there was no increase in mortality.     

Evidence for independent origin of two spring‐spawning ciscoes (Salmoniformes: Coregonidae) in Germany

Combined analyses of mitochondrial DNA (mtDNA) and microsatellite loci were performed to assess the genetic differentiation of two spring‐spawning ciscoes from each other and from sympatric Coregonus albula in two German lakes. Polymorphism was screened at six microsatellite loci and mtDNA for a total of 247 and 94 ciscoes, respectively. Microsatellite data showed a weak differentiation between spring‐spawning Coregonus fontanae and sympatric C. albula in Lake Stechlin ( F _ST = 0–0·008), whereas a significant differentiation was observed between spring‐spawning Coregonus lucinensis and sympatric C. albula in Lake Breiter Luzin ( F _ST = 0·013–0·039). A more pronounced genetic difference was observed between both spring‐spawning species ( F _ST = 0·05–0·128). Shared mtDNA haplotypes among sympatric species within both Lake Stechlin and Lake Breiter Luzin were observed, whereas no haplotype was shared between C. fontanae and C. lucinensis . These results suggest an independent origin for spring‐spawning ciscoes in each lake. Evidence is also provided for mtDNA introgression of Coregonus sardinella into C. lucinensis and C. albula in Lake Breiter Luzin. Postglacially, this species or at least a population which showed mtDNA introgression has colonized the Baltic Sea basin up to the glacial margin that was located between Lakes Stechlin and Breiter Luzin.     

Predation of perch on vendace larvae: diet composition in an oligotrophic lake and digestion time of the larvae

The diet of perch Perca fluviatilis was studied to reveal possible predation on vendace Coregonus albula larvae in an oligotrophic lake. Perch diet changed with the size of the fish: small perch ate mainly zooplankton and the diet shifted more to benthic invertebrates and fishes in larger perch. There were also annual and spatial differences in the diet, probably reflecting differences in the availability of prey animals. Perch predation on vendace larvae was only observed in the area with high availability of the larvae. The result suggested strengthened predation when the density of the larvae increases. According to bioenergetics modelling, the perch population increased natural mortality of vendace larvae only marginally. Food intake of spawning female perch was slightly reduced, whereas spawning males fed similarly to non-spawning males. Hence, the spawning period of perch was only a minor refuge for vendace larvae. Laboratory experiments of perch digestion rate demonstrated that, due to rapid digestion of the small fish larvae, diet sampling interval should not be >2 h in the field.     

不同脊椎动物消化道内5-羟色胺免疫染色细胞的分布

用过氧化物酶——抗过氧化物酶（PAP）法,对乌鳢（Ophiccephalus argus）、中华大蟾蜍（Bufo bufo garaaarizans）、黄喉水龟（Clemmys mutica）、虎皮鹦鹉（Melopsittacus undulatus）和小白鼠（Mus musculus albula）五种脊椎动物消化道内的5-羟色胺（5-hydroxytryptamine,简称5-HT）免疫染色细胞的分布进行了研究。发现各种动物胃肠道（虎皮鹦鹉胃、乌鳢肠及胃贲门除外）均含有5-HT免疫染色细胞,并首次发现黄喉水龟和中华大蟾蜍食道内含有5-HT免疫染色细胞。一般地,各种动物胃内5-HT免疫染色细胞密度最高,十二指肠和大肠次之,小肠最低。5-HT免疫染色细胞位于粘膜上皮或腺上皮细胞间,常有一个或一个以上的细胞突起伸入固有层或肠腔面（或腺腔面）,有些细胞的一端突起伸入固有层,另一端突起伸入肠腔面,表明5-HT免疫染色细胞兼具内分泌或分泌功能。     

Temperature requirements for growth and survival of larval vendace, Coregonus albula (L.)

Water temperatures from 15.0 to 20.0° C are recommended as the most suitable for sustained production of larval vendace, as indicated by the developmental rates, the instantaneous rates of growth, mortality, and the net biomass gain of larvae reared at eight constant temperatures from 4.8 to 22.1° C. The recommended temperatures are optimal when the available food and photoperiod are not the limiting factors. Temperatures higher than 22.0° C will cause increased mortality, whereas temperatures lower than 15.0° C, although advisable when food is limited, will retard larval growth and development.     

Quantification of alizarin red S uptake in coregonid eggs after mass-marking

An easy method to measure the uptake rate of the persistent dye alizarin red S (ARS) during marking of whitefish eggs was established and used to measure the ARS content in three different whitefish species during and at the end of the marking procedure. Those values show that only 6–10% of the ARS in the marking solution will be absorbed by the eggs (0.0061–0.0119 mg per egg). Additional analyses 6, 15 and 36 months after marking showed ARS levels below the response level (<6.9 μg kg^–1).     

Nemerteans of the Great Barrier Reef 4. Anopla Heteronemertea (Valenciniidae)

A new valenciniid heteronemertean, Valencinina albula , gen. et sp. nov. from the Great Barrier Reef province of Australia, is described and illustrated. This is the first record of a valenciniid from Australasian waters.     

Night,day, sunrise,sunset: do fish under snow and ice recognize the difference?

1. Although boreal lakes are ice‐covered for several months annually, little is known about the behaviour of fish under ice. To consider the reasons for diel vertical migrations (DVM) it is important to compare periods under ice as opposed to under open water. Echosounding provides a tool for non‐intrusive continuous monitoring of fish, even in winter. 2. Changes in the vertical distribution of fish through six 48‐h periods were monitored using a stationary, mounted echosounder that beamed vertically either from the bottom up or from the surface down from February to April, 2003. The up‐beaming and down‐beaming transducers were run alternately for 24 h each over the 48‐h period. Standard echo analysis software was used to detect fish traces and estimate the vertical and temporal distribution of fish abundance. Fish were sampled with a winter seine. 3. Prominent diel vertical migration in response to changing light level was detected throughout the study period (late winter to spring). Fish were highest in the water column at sunset and sunrise. In daylight, most detected fish were well below 10‐m depth. The number of fish detected was greatest during the night when they occurred throughout almost the whole water column, sometimes with a considerable number very close to the ice. Fish were mostly vendace and whitefish. 4. It became evident from data from the up‐beaming transducer that at night fish may occupy the layer closest to the surface. These fish would not have been detected if we had only used the down‐beaming transducer. The overall pattern of DVM in winter was very similar to that in summer. The results support the suggestion that DVM is a genetically fixed behavioural trait responding to the contemporary level of illumination.     

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.