摘要:

Atlantic cod (Gadus morhua) were forced to swim in a swim tunnel respirometer until fatigued; oxygen consumption rate (ṀO2) was measured during swimming at incremental speeds until the fish was exhausted and during recovery from exhaustion. Maximal oxygen consumption (ṀO2max) occurred during maximal activity as has been found for other fish species, but at odds with the current paradigm for Atlantic cod. Earlier experiments had drawn the conclusion thatṀO2maxin Atlantic cod occurs during recovery from exhaustive exercise. We found no support for this paradigm in our experiments and we propose that the respiratory physiology of Atlantic cod is not unlike that of other fish

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01580.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The age, growth and reproduction ofChondrostoma polylepis willkommi, an endemic cyprinid from the Iberian Peninsula, was studied for 2 years in a seasonal stream in the Guadalquivir River basin. Annual growth was low. Maximum ages observed were 5+ in males and 7+ in females. There was no significant difference in growth between sexes. Seasonal growth period started in May and continued for 2 to 6 months depending on age. The mean lengths of 1 + and 2+ age‐groups decreased once the growth period had finished, probably related to reproductive stress and adverse ecological conditions, and this could explain the occurrence of Rosa Lee's phenomenon. Both sexes matured at the end of their second year of life (1+). There was a significant difference from 1: 1 in the overall sex ratio of 334 males to 464 females. Reproductive period started in March and lasted until May.Ch. p. willkommiwas a multiple spawner that released two batches of eggs per female each year. The regression between fecundity (F) and fork length (l., mm) was:F=6.20 103L.2.78. In females from age 2 + onwards, relative annual investment in somatic growth and reproduction was equivalent, implying that the same energy was allocated to reproduction as to maintenance/growth. Compared with otherCh. polylepispopulations, the life‐history patterns of this population, located in a small and seasonal stream in a southern latitude, were characterized by a low annual growth, a trade‐off between reproduction and growth/maintenance, early maturity, low number of age‐groups and high fecundity from multiple sp

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01581.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Predation encounters were staged in the laboratory to compare prey responsiveness, predator error rate, and predator capture success for juvenile codGadus morhua(a suction feeder) and herringClupea harengus(a biting predator) preying on herring and plaicePleuronectes platessalarvae. Trials were conducted at near natural temperature extremes for the larvae (8 and 13°C) to assess the importance of water temperature to the interaction. Herring larvae were significantly more responsive to attacks by herring than were plaice larvae (5·7 vs 0′0%). The two prey species were equally responsive to attacks by cod (2–6vs10%). Cod caught 91% of herring larvae attacked and juvenile herring caught 87%. Cod were successful in 96% of attacks on plaice, but juvenile herring caught significantly fewer (83%) plaice larvae. For each predator species, capture success did not vary significantly with prey species. Overall capture success for herring was significantly lower than that for cod. Responsiveness of herring larvae to attacks by juvenile herring increased with temperature, but predator error rate and capture success were not altered by water temper

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01582.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Variation in beach seine catches was examined in two juvenile flatfish populations (Port Erin, Isle of Man and Porto Pirn, Azores) to determine the importance of diel cycles while controlling for tidal rhythmicity. At Port Erin sampling was undertaken at each low water on consecutive days over a 2‐week period in May/June and September 1991. There was no periodicity in the catches of plaice (Pleuronectes platessa) in May/June, but in September catches were higher at night. Other flatfish species (Limanda limanda, Pleuronectes flesus, Scophthalmus maximusandS. rhombus) sampled at Port Erin were nocturnal. At Porto Pirn, Azores, fish were sampled over 24 h each month from July 1989 to June 1990 and at each low water over a 2‐week period in July 1991. The only flatfish species present wasBothuspodas, which had a diurnal pattern in catches over a 1‐year period. Sampling at low water in July gave high catches at both midnight and m

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01583.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Mitochondrial (ml) DNA genotypes of grey mullet (Mugil cephalus) from ocean basins around the world were analysed to estimate the amount of genetic differentiation in this cosmopolitan but mostly coastally‐restricted species. Extensive genetic diversity was observed. Among 115 specimens from nine locales, 26 different haplotypes were detected using a battery of 13 restriction endonucleases. In phenetic analyses, these haplotypes grouped into seven distinct clusters whose members were in almost perfect accord with the geographic sources of the samples. Thus contemporary gene flow between the widespread collection locales must be absent or nearly so. Results contrast with the relative uniformity in mtDNA composition previously reported for populations of some circumglobally distributed pelagic fishes, and demonstrate that certain marine fishes with cosmopolitan distributions can exhibit pronounced population genetic structure even in the face of morphological conservatis

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01584.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Resistance to experimental infections ofIchthyophthirius multifiliiswas investigated in the poeciliid fishXiphophorus maculatus, X. variatusand their two reciprocal hybrids. A third species, the goodeidAmeca splendens, was infected for comparative purposes. Infection data were analysed using a generalized linear interactive modelling package (GLIM). Infection levels were not significantly influenced by the sex of the fish, temperature, or speciestemperature interactions, but body area and time of infection did affect susceptibility. After accounting for variation due to these factors, it was shown that the two reciprocal hybrids ofX. maculatusandX. variatushad significantly lower infection levels than either parental stock. Heterosis,H, was calculated from both raw data (16.2%) and from modelled values (31.3%) after removal of environmental factors. This confirms the existence of genetic factors determining resistance to /.multifiliisinfection and has shown that gains in resistance can be made through hybridization.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01585.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Several hundred recently‐metamorphosedPetromyzon marinuswere caught during heavy freshwater discharge in the River Severn on the night of 30 November/1 December 1988. The total lengths of a subsample of 42 males and 82 females ranged from 155 to 218 mm, with a mean of 182 mm in both sexes. The buccal funnel, eyes, fins and the teeth on the suctorial disc and tongue‐like piston were very well‐developed. When placed in full‐strength sea water, the lampreys fed on bass (Dicentrarchus labrax), leaving prominent scars on these hosts. The morphology, body size and time of capture of the River Severn sea lampreys provide very strong circumstantial evidence that these lampreys had been feeding for some weeks. Since they were caught when moving downstream and were capable of feeding in sea water, they were presumably about to begin their parasitic mari

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01586.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Anatomic and cytological studies of some 110 species of deep‐sea eels of among others the families Congridae, Colocongridae, Heterenchelyidae, Synaphobranchidae, Nettastomatidae, Nemichthyidae, Serrivomeridae, revealed a very high diversity in the visceral organs, especially gonads, guts and kidneys and their relation to the anal opening.The ovaries of various species were either monocyclic, producing eggs periodically, or polycyclic with frequent egg production. Some testes showed synchronous and others asynchronous sperm production. In some of the families, such as Heterenchelyidae, all the gonads are situated post‐anally, in the tail, whereas in Congridae the extent of penetration varies in the different genera, indicating that this family is an artificial one. As some gonads of a few species were found to harbour gametes of the two sexes, the possible occurrence of hermaphroditism is discussed. Melanization of gut was observed in numerous species produced by the penetration of pigmented tissue between the muscle layers of the gut wall or between these and the gut epithelium, this differing between various taxa and in young and adult specimens. The melanization of gut or parts of gut prevent slight (emitted by the swallowed bioluminescent prey) from being seen outside, and in this way protects the eel from predation. Pigmentation also occurs in the kidneys and other explanations for melanization are therefore discussed. In numerous species the gut, kidney and gas chamber partially penetrate into the tail, and as with the gonads, these characters can also be used on eel taxon

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01587.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The efficiencies of water absorption from the guts of the larvae of herring (Clupea harengusL.) and turbot (Scophthalmus maximusL.) were estimated by two methods, The first method was based on the differences in the rates of accumulation, by drinking, and clearance from the gut of radiolabelled inert markers. The second method used the equilibrium level of radioactivity in the larvae to measure the concentration of the markers in the gut above background as water is absorbed from the gut. Water absorption efficiencies for herring larvae drinking sea water were estimated to be 77% using both methods. When external salinity was reduced to 50% sea water, drinking rates and water absorption efficiency in herring larvae fell substantially.Estimates of water absorption efficiency of seawater‐adapted turbot larvae were similar (71–84%) to that of herring using both methods. Although temperature had a marked effect on both the rate of drinking and water absorption, there was no significant thermal effect on the efficiency of absorption from the guts of turbot larvae. The limitations of the techniques and the implications of the estimates in terms of water balance in fish larvae are discus

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01588.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Levels of sulphated 17α20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β‐P; the oocyte maturation inducing steroid) in blood plasmas of sexually mature male and female rainbow troutOncorhynchus mykiss, were very low in comparison to those of the free steroid. However, relatively large amounts were found in urine of both sexes.Catheters were inserted into the urinary bladders of unovulated and ovulated females and of ripe‐running males, and the fish then placed in spawning channels. Three‐hourly urine samples were collected between 09.00 and 18.00 hours and then a 15‐h sample between 18.00 and 09.00 hours the next morning. Measurements were made of 17,20β‐P‐sulphale, testosterone glucuronide (T‐G) and 17β‐oestradiol glucuronide (E2‐G). In females, the highest rates of excretion of E2‐G, T‐G and 17,20β‐P‐sulphate were found in unovulated, ovulating and ovulated females, respectively. The rates of excretion of 17,20β‐P‐sulphate, T‐G and E2‐G in ovulated females were unaffected by the presence of a male. id males, however, there was a sharp increase in the rate of excretion of 17,20β‐P‐suiphate and T‐G in fish which were paired with an ovutated (nesting) female. A similar increase was

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1994.tb01589.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY