摘要:

This study presents a cytogenetic analysis of the genusDicentrarchus, represented by two species,D. labraxandD. punctatus. The karyotypes are very similar, even after staining with different techniques. Both species show 48 subtelocentric and acrocentric chromosomes, gradually decreasing in size. One pair of small size chromosomes has heteropycnotic and heteromorphtc short arms of longer size. These short arms are C‐ and Ag‐positive, i.e. nucleolar organizer regions, NORs, are located there. Constitutive heterochromatin is also evident as a subcentromeric band on the long arms of a large chromosome pair. CMA3‐staining confirms the location and the heteromorphism of NORs. DAPI and quinacrine produce homogeneous staining of chromosomes. A review of cytogenetic studies on ‘serranid’ species is also

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00567.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Data gathered between 1988 and 1992 document the spread of the parasitic nematodeAnguillicola crassusamong eels in the tidal Thames catchment. Eel samples revealed a parasite prevalence ranging between 12 and 32% with a variation in intensity of infection of between one and five nematodes per infected host. Differences in the salinity regime between sampling points may be linked to the range of levels of infection in eels because of the saline tolerance limits of parasite developmental stages. The euryhaline teleost, the smelt (Osmerus eperlanus) found throughout the tidal river has been shown by others to be able to transfer nematode larval stages experimentally to large eels. Smelt found in the tidal Thames thus could possibly act as a further intermediate host to the eel population. The results support the theories proposed by previous workers that the parasite originally entered the tidal Thames via the commercial trade in live eels.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00568.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Measurements of embryonic volume revealed regulation capability before hatch. Water diffusion permeability, determined as tritiated water efflux, was found to be low, but within the range for fish eggs. The perivitelline fluid is readily interchangeable with the external medium due to a high chorion permeability to both water and salt.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00569.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

A large number of sterile burbot (Lota lota) have been recorded on the northern coast of the Bothnian Bay (29–93%) and in Lake Kemijärvi in northern Finland (44%). A suggested hypothesis is that the burbot needs one or more rest years between spawning seasons to restore the fat reserves in its liver. A comparison made here between the three burbot populations (brackish water, lake and river), did not confirm this hypothesis. The somatic condition index, liver index and intestine index of the normally‐spawning river burbot, in which the percentage of non‐spawning fish was 14%, were considerably lower than those in spawned or sterile coastal or lake burbot, so that poor nutrition state did not result in sterility or rest

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00570.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Livers of juvenile cabrilla sea basses (Serranus cabrilla) were subjected to light and electron transmission microscopy following different periods of maintenance in an aquarium. Since this fish is easy to feed in captivity and the hepatic structure was found to be comparable at the four periods tested (0, 5, 10 and 20 days), both at the histological and ultrastructural level, the liver ofS. cabrillacould be an available model for marine contamination experimental studies. As in other fish species, it is not possible to distinguish the portal lobules and the triads. The Melano‐Macrophage Centres contain tipofuscins, ceroids and haemosiderin, but they do not contain any melanin. The hepatocytes are arranged in cords (two cells thick), and, at the ultrastructural level, they show numerous microvilli in the perisinusoidal and canalicular areas. The hyaloplasm includes a considerable amount of glycogen and some lipid droplets are occasionally observed. Mitochondria, rough endoplasmic reticulum and the Golgi apparatus are relatively scarc

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00571.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The diel timing of displacement of emerging brown trout (Salmo trutta) was studied by trapping the alevins at the downstream end of three experimental channels. The presence of phosphorescent landmarks on the substrate delayed the catches during the first hours of complete darkness, but increased them during twilight. During daylight, the presence of the landmarks was associated with greatly increased numbers of free‐swimming fishe

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00572.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

A quantitative comparison of the grazing behaviour of youngOreochromis niloticusfeeding on the planktonic cyanobacteriumMicrocystis aeruginosaand a periphytic community dominated by the cyanobacteriumOscillatoriasp., determined that biomass ingestion rates of fish filter‐feeding on planktonic cyanobacteria were significantly lower than those surface‐grazing on periphyton. Comparisons of published laboratory data on filter‐feeding with field data on algal ingestion rates suggest that filter‐feeding may be a relatively unimportant method of ingestin

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00573.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

When male hybrids of Atlantic salmon × brown trout were backcrossed to female Atlantic salmon, approximately 1% of diploid progeny hatched. These were shown to exhibit recombinant genotypes when examined electrophoreticalty at five enzyme loci. This is the first confirmation of genie recombination in backcrosses of these species. Triploidization greatly increases the proportion of backcross progeny which hatch

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00574.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The effect of starvation‐refeeding on protein mobilization in the lateral line, lateral (midway between lateral line and dorsum) and dorsal parts of white sturgeon (Acipenser transmonlanus) white epaxial muscle (type IIB) were compared by measuring muscle cross‐sectional fibre areas. Effects on red (type I) and pink (type IIA) muscle were also studied. Fish starved throughout the experiment (5 weeks) showed a uniform response, i.e. the cross‐sectional fibre area decreased at all sampled locations in the white muscle as well as in red and pink muscle. Fibre size in fish refed for 3 weeks after 2 weeks of fasting (S/F) was reduced mainly in the dorsal regionofthe white muscle. Starvation for 3 weeks after 2 weeks of initial feeding (F/S) also reduced fibre size mainly in the dorsal regions of the white muscle and in the pink muscle. The results indicate that in sturgeon exposed to short periods of low food availability, protein is utilized preferentially from trie more dorsal regions of the white epaxial muscle and from pink muscle. Protein in white muscle located closer to the lateral line and in red muscle seems to be spared. With the onset of refeeding, protein deposition occurred rapidly in pink muscle, but was delayed significantly in the dorsal part of the white m

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00575.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Alternating periods of food deprivation with those of unlimited provision of food depressed the growth of Arctic charr,Salvelinus alpinus, below that of controls. Fish that were deprived of food and then fed on alternate weeks (1:1) were larger than those that were exposed to periods of 1 5‐ or 3‐week deprivation and feeding (1·5:1·5 or 3:3). On receiving excess food supplies following 24 weeks on the restricted feeding regimes the previously‐restricted fish grew more rapidly than the controls. The greatest compensatory growth was displayed after the 3:3 regime, followed by the 1·5:1·5and then the 1:1 feeding regime. At the termination of the experiment there were no significant differences in body weight between fish fed according to the different regimes during the period that food restriction was imposed. Growth patterns of the immature males and females were similar, but mature males were significantly lighter than the immature fish by the end of the experiment. Both immature and maturing fish displayed a compensatory growth response on return to adequate feeding. Beginning food restriction in May did not influence the proportions of male fish (c. 60%) which were mature in t

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00576.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY