摘要:

Electron microscopic analysis of U V‐irradiated tilapia sperm showed that with irradiation dose of 1800 J m−2min−1, an irradiation duration of 0.5 min caused decondensation of sperm chromatin. This phenomenon of chromatin decondensation reached a peak after l.5min of irradiation, where ∼ 15% of the sperm showed total decondensation, and was less apparent after 3 min of irradiation or more. Damage to the cytoplasmic membrane and nuclear envelope could be seen in cells that underwent total decondensation. As the duration of irradiation increased, cytoplasmic membrane and nuclear envelope defects appeared more severe, the mitochondria were affected and appeared as empty capsules, and sperm cells tended to lose their tails. Based on these results and others reported in the literature, we propose an explanation for the ‘Hertwig curve’ obtained in tilapia using UV irradiation. Sperm cells with decondensed chromatin and damaged cytoplasmic membrane and nuclear envelope, activate the ‘developmental switch’ when they penetrate the egg, but their pronuclei are subjected to cytoplasmic nuclease digestion. Consequently, the maternal pronucleus is the only functional pronucleus in the zygote, and therefore, only haploid embryos with the exclusive maternal genome are formed. If the paternal pronucleus is not digested, these embryos will die due to improper expression of the

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00301.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Daily lapillus growth increments were used to determine age and growth parameters forScarus rivulatus(Valenciennes) andCtenochaetus binotatus(Randall) from reefs off Lizard Island in ihe northern Great Barrier Reef. The growth ofS. rivulatusincreased after settlement whilst growth ofC. binotatusdecreased after settlement. A check found in the otoliths of both species, and attributed to settlement, was estimated to be from 28 to 47 days forS. rivulatusand from 47 to 74 days forC. binotatus.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00302.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Mitochondrial DNA (mtDNA) variation was examined in 209 Atlantic salmon from two river systems, the R. Itchen in Hampshire (Southern England) and the R. Conwy (North Wales). Within each system, five spawning sites were sampled. Four enzymes (AVA II, HAE III, HINF I and MBO I) revealed restriction fragment polymorphisms that were informative. Ten clonal lines were observed. These clones were differentially distributed between the two river systems and single clonal types were found to predominate at several spawning sites. MBO I variants were found in salmon from the R. Itchen but not the R. Conwy. A significant heterogeneity in frequency distribution of clonal lines between parr and smolt assemblages of the same year class within the R. Itchen was detected. This heterogeneity suggests that differences in survival or migratory behaviour may be identified by changes in mtDNA clonal frequencies.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00303.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Eggs of the whitefin gudgeon,Gobio albipinnatusLukasch, were artificially obtained from adults caught in the Danube River near Vienna, Austria. Average diameter of hydrated eggs was 1.5 mm (S.D.=0.05). Incubation times decreased exponentially from 8 to 24° C. Mortality of embryos was lowest at 16° C and highest at 8° C. Total length at hatching ranged from 4 to 5.7 mm. First feeding occurred 3 days after hatching. Growth with excess food was observed for 3 months in the laboratory at 16 and 20° C. Highest growth rates obtained were 11 % fresh weight day‘. Field samples of 0+G. albipinnatusindicated four cohorts occurring in a Danube backwater. Growth in the backwater was comparable to juveniles growing at 20° C in the laboratory. From information on growth and incubation we estimate that spawning starts in the middle of May and proceeds at 2‐weekly intervals until the end of June. Incubation time and growth of 0+G. albipinnatusclosely resembles that ofGobio g

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00304.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The diet, prey selection, and growth of larval and juvenile Oneida Lake burbot,Lota lota(L.), was investigated from the time of first hatch in mid‐April until their disappearance from the pelagic zone at the beginning of June. Mean length increased exponentially from 3–20 mm on 18 April to 15–00 mm on 29 May. The number and size of prey in burbot stomachs, and the prey size most selected by burbot increased as they grew. Prey width, not prey length, limited the size of prey ingested. The smallest burbot ate and selected highly for the largest prey they could ingest, but older burbot did not. As burbot grew, prey selection was highest first for the rotiferAsplanchna, followed by copepod nauplii, then cyclopoid copepods.Daphniaand calanoid copepods and cyclopoid copepods were selected to similar degrees by 29 May. For a given size, however, cyciopoid copepods were selected more strongly than any other prey type from 18 to 29 May. There were no significant differences in prey selection among offshore, nearshore, and onshore habitats, nor among depths in the offshore ha

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00305.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Daily increment formation was demonstrated in the sagittae of the three‐spined stickleback,Gasterosieus aculeatusL., under both laboratory and field conditions. The onset of daily increment formation coincided with the day of hatching. The main sources of inaccuracy in age determination resulted from difficulties in resolving narrow increments in the sagittae of fish held at low temperatures and the increasing incidence of checks with age. The advantage of daily increments for investigating growth in this species was demonstrated from a comparison between increment‐derived age‐at‐length data and length‐at‐capture data, since the latter significantly under‐estimated early growth rate within

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00306.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Using light and electron microscopy, enzyme‐histochemistry thin‐layer chromatrography and photometry the functions of the spermatic ducts in salmonid fishes (rainbow trout,Oncorhynchus mykiss, Arctic charr,Salvelinus alpinus; grayling,Thymallus thymallus; whitefish,Coregonussp.) were investigated. During spawning the spermatic duct of the Salmonidae has a high secretory activity: it synthesizes steroids, lipids (triglycerides, fatty acids, cholesterol esters, phosphatidylcholine), monosaccharides (glucose, fructose), proteins and enzymes (acid and alkaline phosphatase, glucuronidase and proteases). It is important for storage and resorption of spermatozoa. Interspecific differences exist in the storage capacity for se

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00307.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The stomach contents of samples of the mugilidLiza ramada(Risso, 1826), captured at Alcochete (brackish water zone of the Tagus Estuary) differed from those from Vala Nova (freshwater zone of the same estuary).In the freshwater zone of the estuary the mullet ingested preferentially planktonic micro‐algae, while in the brackish water they ate benthic micro‐algae.The stomach contents from Vala Nova showed a higher diversity of food items, compared with those from Alcochete. At Alcochete the Naviculales (numerical frequency, 82%) was the most representative order, while at Vala Nova it was the Coscinodiscales (61%) and the Chlorococcales (16%).In fresh water, the stomach contents contained about 25–4% organic matter, while at Alcochete only 8.7% was found.In the brackish water zone the ingestion rhythm was related to the tidal cycle, attaining a maximum during the high tide and a minimum at low tide.At Vala Nova the mullet ate regularly throughout the day. showing a slight increase at dawn and dusk. Apparently, the fish remained inactive by night, at both loca

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00308.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The present study was carried out on the Catalan coast, the northern limit of the geographic distribution ofPomatomus saltatrix(Linnaeus, 1766) in the Mediterranean. Within the area studied, both larvae and adults were more abundant in the southern part, where surface temperature was slightly higher than in the north. Spawning ofP. saltatrixwas limited to the warmest months, from July to September, when the surface temperature was about 25° C, The most common larval sizes, between 2.25 and 2.75 mms.l., were distributed over the continental shelf, and the greatest concentrations were found between 20 and 100 m, suggesting an inshore spawning. Larvae, including the smallest sizes, were found in the most superficial layers and no evidence of vertical migration was observed. The species was regularly fished in the southern zone, maximum monthly catches ranging between 10–20 tonnes. The presence of adults in the coastal zone showed a marked seasonality closely related to temperatur, the lowest catches corresponding to the coldest mont

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00309.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Atlantic salmon (Salmo salarL.) alevins hatched from eggs transferred from high‐ to low‐Na water at 250° days, before the onset of the phase of increasing whole egg sodium content (at ∼380°days), showed a significantly reducedKmfor Na+transport, whereas transfer at 400° days did not produce any change inKm. Alevins hatched from eggs given acid shocks of 1, 3, 7 or 14 days duration initiated at 250 or 400° days showed no significant changes in Na+transporterKm. Extended acid exposure (38 days) from 250°days to hatching resulted in a slight lowering ofKm(P<0.05). A 24‐day acid exposure from 400°days to hatching had no effect on Na+transporterKm. Alevins hatched from eggs incubated throughout in acidified water had a significantly reducedKmcompared to controls (P<0.01).The timing and duration of periods of Na depletion of eggs is considered with respect to environmental induction of increased Na transporter affinity in teleost embryos as a mechanism of long‐term physiological adaptation to the gradual acidification of

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1993.tb00310.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY