摘要:

Dace lay adhesive eggs in fast‐flowing water which they attach to the gravel substratum. Artificial spates, similar in magnitude to those occurring naturally during the incubation period in early spring, produced transient peaks in egg drift. Even a severe spate caused the loss of only 2.4% of the estimated egg population. Dace eggs are negatively bouyant and, at a current speed of 50 cm S‐1and a depth of 26 cm, only 2.4% of dace eggs introduced at the surface failed to attach to a gravel substratum within 6 m of the point of rele

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05817.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The downstream movement of young trout and salmon in relation to water velocity was studied in simulated river channels. The results are interpreted as showing that these young salmonids pass through a short period when they are very vulnerable to downstream displacement by flow. Behavioural differences between the two species are considered with the influence on fish movement of changing rate of water velocity, light and temperature.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05818.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Sarotherodon mossambicus,Cyprinus carpioandSalmo gairdneriwere acclimatized at temperatures of 15, 20 and 25° C in order to study physiological responses of blood to temperature fluctuations in the laboratory.Cyprinus carpioexhibited the greater ability to survive at these temperatures.Sarotherodon mossambicusexperienced osmoregulatory collapse at 15° C which also occurred in trout at 25° C. This was associated with acid‐base malfunction in the t

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05819.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Starvation resulted in considerably increased deposition of melano‐macrophages within the spleen and kidney ofPleuronectes plalessa, Salmo gairdneri, Xiphophorus helleri, andTilapia zilliialso within the liver and spleen ofScyliorhinus canicula. These results suggest that catabolic tissue breakdown is a major factor contributing to the formation of the pigments within melano‐macropha

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05820.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The occurrence, size and maturity changes ofEubothrium fragilehave been studied in postlarvae, juveniles and adult twaìte shad,Alosa fallax, from several locations in the River Severn. Parasites were only found in adult shad and not in post‐larvae or juveniles. No juvenile or recently acquired cestodes were identified as such, but adults were present in shad throughout the whole period of their spawning migration. A large proportion of the parasites were gravid upon arrival in the river and, although eggs were subsequently released into fresh water, there was no loss of cestodes from the fish. It was concluded thatE. fragileis a marine species, that the parasites found in adult shad in fresh water were the residue of a marine life cycle and that the eggs released in fresh water were part of the parasite's natural reproductive wastage. The distribution and biology ofE. fragilewere discussed and it is considered that it is typical of the marine species of the gen

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05821.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Grey mullet,Mugil cephalus, collected from ponds were induced to spawn with carp pituitary homogenate and human chorionic gonadotropin (HCG) at 30%osalinity and 26° C. The spontaneously spawned and fertilized eggs were transferred to sea water of different salinities in the range of 5–70%o, either at the 2‐blastomere or the gastrula stage. Those eggs transferred at the gastrula stage were more tolerant to the salinity change than were those transferred at the 2‐blastomere stage. The eggs did develop to the embryonic stage within the salinity range from 5 to 60%o. Hatching occurred in all salinities between 10 and 55%o. However, no larvae survived at 10 or at 55%o. The optimal salinity range for eggs incubating at 22.0–25.5° C was from 30 to 40%osalinity, with the pea

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05822.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The reproduction of summer flounder,Paralichthys dentatus(L.), occurring in the Middle Atlantic Bight was studied from 1974–1979. Males dominated the length interval between 21–35 cmt.l.and were essentially absent in samples>55 cmt.l.Females were more abundant in all length intervals>45 cmt.l.Length at maturity ranged from 24–27 cmt.l.for males and from 30–33 cmt.l.for females which coincided with length at age two. Ovarian egg diamerter frequencies indicated summer flounders are serial spawners and the trend in mean and maximum maturity indexes (% ovary weight of total fish weight) indicated spawning began in September and continued through February in 1975 and probably into March in 1976. Annual condition cycle of males peaked in September and was lowest in April while females’ cycle reached a maximum in October which coincided with peak spawning time. Fecundity was related to length, weight and ovary weight for 1974–1977 and the length‐fecundity equationF= 0.0007975L3.402was found to be the best predictive relationship. The overall reproductive strategy of summer flounder was discussed and apparently tends to maximize reproductive potential through an extended spawning season, early maturation, high fecundity, serial spawning and extensive spawni

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05823.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The effect of various external concentrations of sodium and calcium on the survival and hatching of brown trout,Salmo trutta, eggs at pH 4.5 was tested. A calcium concentration of approximately 10 ppm (500 μE l−1) enables freshly fertilized eggs to survive whereas eyed ova are tolerant of deionized water acidified by sulphuric acid with no other ions added. Concentrations of sodium and calcium of 1 ppm (44 and 50 μE l−1, respectively) are sufficient to ensure the successful hatching of eyed ova and subsequent survival of the alevins. At pH 4.5 hatching is prolonged by the alevins passing through a temporary encapsulated

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05824.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Protein synthesis in liver, gill and muscle tissue was measuredin vivoby constant infusion of14C‐tyrosine in fed and fasted freshwater rainbow trout,Salmo gairdnerii, at 12° C. Synthesis rates (percentage of tissue protein synthesized per day) were 15‐17% in liver, 4–5% in gill and 0.38% in muscle of fed fish. Liver and gill synthesis rate showed no significant change in fish that had been without food for 15 days, whereas muscle protein synthesis fell to 0.09%. The greater susceptability of muscle protein synthesis to fasting, possibly results from the greater proportion of synthesis retained as growth in this tissue. Growth rates indicate little change in protein turnover in the muscle but increased protein degradation with fasting. The difference between fed and fasted synthesis rates in muscle may be used as a measurement of potential growth rate for a particular s

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05825.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Changes in the size of the infrapopulations of metacercariae ofDiplostomum gasterosteiandTylodelphys clavatawere studied in a small lake for a period of seven years in perchPerca fluviatilis.Tylodelphys clavataappeared in the lake at the commencement of the study and its subsequent population increase and changes were typical of those of a species recently established in a new habitat. Population size increased slowly at first, then rapidly, then declined again as population density approached equilibrium level. By contrast, the population size ofD. gasterosteideclined throughout the study. Two processes were responsible for the decline: a decrease in the proportion of fish carrying heavy infections which was continuous throughout the seven years and a dramatic decline in recruitment rate in young fish during the last two years. In earlier years recruitment rate had changed annually and changes in overall infrapopulation size had largely reflected the recruitment rate two years previously. It was concluded that these two processes were independent of each other and related to changes in the population density of other species of eyeflukes. The decline in the proportion of heavily infected fish was significantly negatively correlated with the increase in population density ofT. clavataand the decline in recruitment rate in young fish was coincident with the appearance and infrapopulation increase ofT. podicipinametacercariae in the eyes of young perch. It is suggested that these two species interact negatively withD. gasterosteiand are currently partitioning the perch habitat between themselves.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1981.tb05826.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY