摘要:

The role of compensatory mechanisms in the population dynamics of lake trout in the Michigan waters of Lake Superior was explored during three time periods: the pre‐sea lamprey period, prior to 1950 when lake trout were at a relatively high abundance and the fishery was the primary source of lake trout mortality; the sea lamprey dominant period, from 1951 to 1961 when lake trout were at a very low abundance due to sea lamprey predation and overexploitation; and currently, from 1985 to 1993 when wild lake trout abundance was at a moderate level. The role of compensatory changes in growth and fecundity rates of lake trout in the Michigan waters of Lake Superior was evaluated using a life table approach. Individual growth and fecundity rates were calculated and compared between time periods. These rates were used to determine age‐specific fecundity which, along with age‐specific survival, were incorporated into a Leslie projection matrix to calculate the finite rate of population increase (λ). Individual growth rates and age‐specific fecundity rates changed in response to the different levels of lake trout abundance during each of the study periods. Lake trout during the sea lamprey dominant period, which experienced the lowest abundance and highest mortality levels, exhibited the fastest individual growth rates and the highest age‐specific fecundity. These high rates contributed to the relatively large compensatory scope exhibited by lake trout during the sea lamprey dominant period as compared to lake trout during the pre‐sea lamprey or the current periods which are associated with higher levels

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00077.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The average lethal concentration of un‐ionized ammonia (48‐h LC50NH3) has been determined by the static assay for larvae (0.48 mg l−1) and alevins (0.92 mg l−1) of ‘pacamã’Lophiosilurus alexandri.Studies by light and scanning electron microscopes at the greatest concentration of NH3(0.99 mg l−1for larvae and 1.5 mg l−1for alevins) have shown that the changes in the cells and branchial tissue were more intens

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00078.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Synbranchus marmoratus, the ‘swamp eel’, is a protogynous diandric fish. The primary and secondary males can be distinguished from each other easily by differences in gonadal morphology. Primary males have lobular, unrestricted testes with central efferent ducts. The secondary male has a ‘lamellar’ testis, efferent ducts are present in the ventral region (new formation), lateral supports and it is covered by the former ovarian capsule. The length of primary male varies from 13 to 88 cm while secondary males range from 56 to 91 cm. Transitional individuals vary between 45 and 60 cm in length. The swamp eel population studied is composed of 80% primary males and 20% secondary males. Although gonadosomatic indices are always higher in primary males, they increase in secondary ones as the newly acquired stage progresses. The lamellar organization of the gonad of secondary males, the absence of this kind of testis in individuals smaller than 56 cm, and the presence of hermaphroditic fish, is evidence for protogyny in this

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00079.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A non‐uniform distribution of cutaneous chloride cells was found in the early, pre‐feeding larval stages of herringClupea harengus. Chloride cells on the head, yolk‐sac and trunk regions were unevenly distributed, whereas more densely packed chloride cells were observed in the pericardial and prebranchial regions. The pattern of chloride cell distribution changed during development and two distinct changes are described. The density of choride cells on the ventral trunk increased substantially during the period of yolk absorption, presumably due to contraction of the yolk sac and selective retention of yolk‐sac chloride cells. Also during this period the cells on the lateral body wall increased in number and became distributed in segmental bands overlying the myosepta. Most chloride cells were found in association with the haemocoel or primordial blood vessels. Superficial segmental blood vessels were not found in the early larva, but the segmental bands of chloride cells overlay nerve tracts in the myosepta which were tentatively identified as the focal innervation of myotomes. It is concluded that both the circulatory system and the peripheral nervous system may play a role in determining chloride cell distribution in early

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00080.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Mitochondrial DNA (mtDNA) restriction analysis was used to examine the evolutionary and taxonomic relationships among 11 taxa of the subfamily Salmoninae. The generaBrachymystaxandHuchowere closely related, diverging by sequence divergence estimates of 3.1%. Because the mtDNA sequence divergence between blunt‐ and sharp‐snouted forms ofBrachymystax(2.24%) was similar to divergence level ofBrachymystaxandHucho, then taking into account the distinct morphological, ecological and allozyme differences between them, it is possible to recognize these forms as two separate species. The subgenusParahuchoformed a very distinct group differing by 6.35–7.08% (sequence divergence estimate) from bothBrachymystaxandHuchoand must be considered as a valid genus. The UPGMA and neighbour‐joined phenograms showed that the five genera studied are divided into two main groupings: (1)Hucho, BrachymystaxandSalvelinus; and (2)OncorhynchusandParahuchospecies. The mtDNA sequence divergence estimates between these groupings were about 8.1%. However, the subsequent bootstrap analysis of mtDNA RFLP data did not support the monophyly of the latter grouping. The concordance of morphological and mtDNA phylogenetic patterns is di

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00081.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Fed and 3‐day fasted inland (average mass: 6.97 g) and anadromous (average mass: 6.54 g) striped bassMorone saxatilisfingerlings were held in dipnets above water for 5 min in groups of six. Severity of the response to this handling was measured by whole‐body glucose, glycogen, and lactic acid in non‐handled bass (considered control level), and then at 30 min, 1, 6, 12, 24 and 48 h recovery. At resting levels, both fed and fasted inland bass showed significantly higher concentrations of the whole body variables than anadromous bass. All four groups of bass showed an increase in lactic acid and glucose immediately after handling, with a concomitant decrease in glycogen. Peak levels of glucose and lactic acid were similar in the four groups. Fasting did not have an effect on the glucose and lactic acid responses, but did affect the glycogen response. The two fasted groups did not return to control glycogen concentrations during the 48‐h recovery period. By 48 h, both glucose and lactic acid had returned to control levels. It is concluded that inland and anadromous strains of fingerling striped bass do not differ in their sensitivity to an acute handling stress. Recovery of glycogen energy stores following handling is much better if fish are not fasted before h

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00082.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Eggs of the tambaquiColossoma macropomumwere incubated at 28 and 31) C. Somitogenesis started shortly after the formation of the neural plate and notochord. New somites were added at the rate of one every 13 min at 28) C and one every 11 min at 31) C. Myogenesis started in the most rostral myotomes at the 9‐somite stage and proceeded in a caudal direction. Mononuclear myotubes with the morphological characteristic of muscle pioneer cells were observed lateral to the notochord. The majority of myotubes were formed from the fusion of 3–6 spindle‐shaped myoblasts. Myofibril synthesis started soon after cell fusion at the periphery of myotubes. Close membrane contacts and ‘gap’‐type junctions were observed between myotubes, immature muscle fibres and at the inter‐somite boundary, suggesting that the cells were electrically coupled. Embryos exhibited rhythmic movements at the 20‐somite stage, and hatched at the 29–30‐somite stage 15–18 h post‐fertilisation (PFT) at 28° C and 11 h PFT at 31° C. Larvae hatched at a comparatively early stage of development prior to the completion of somitogenesis and the formation of eye pigment, pectoral fins and jaws. The myotomes comprised a single superficial layer of well‐differentiated muscle fibres which contained abundant mitochondria, overlying an inner core of myotubes (presumptive white muscle layer). Differentiation and growth during the larval stages was extremely rapid, and the juvenile stage was reached after littl

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00083.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Oxygen consumption rates were measured in a school of 56 horse mackerelTrachurus trachuruswhile at rest and while swimming at steady sustained speeds. Resting values of 38.76 and 42.10mg O2kg−1h−1were measured in a sealed cylindrical tank (535 l) while observing that the fish school remained neutrally buoyant and inactive with only gentle pectoral fin movements and no swimming motion. The same school was trained to swim with projected light patterns within a 10‐m diameter annular doughnut respirometer. The oxygen consumption increased from the resting level through 51 mg O2kg−1h−1at the slowest swimming speeds of 0.29 m s−1(0.95 L s−1) to around 259 mg O2kg−1h−1at the higher measured swimming speed of 0.87 m s−1(2.82 L s−1). The data fitted a curve where oxygen consumption rose in proportion to velocity to the power of 2.56 with the intercept at the resting level. The maximum sustained speed (80 min) of 1.12 m s−1(3.63 Ls−1) was not achieved within the respirometer but corresponded to an estimated oxygen consumption of 458.33 mg O2kg−1h−1giving a scope for aerobic activity of 419.02 mg O2kg−1h−1. At a speed of 0.87 m s−1, there was a lower bound on the aerobic efficiency of at least 38% and at 1.12 m s−1, the highest aerobic speed, of 40%. Sustained speeds swum in a curved path as here should be increased by 5% for a straight path giving a maximum

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00084.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Growth and energy budget were measured for three sizes (2.4, 11.1 and 22.5 g) of juvenile white sturgeonAcipenser transmontanusheld at 18.5° C and fed tubificid worms at different levels ranging from starvation toad libitum. For each size‐class, specific growth rate increased linearly with increasing ration, and conversion efficiency was highest at the maximum ration. Growth rate decreased with increasing fish size at the maximum ration, but increased with size at each restricted ration. Conversion efficiency increased with increasing ration for each size‐class and was usually highest at the maximum ration. Faecal production accounted for 3.2–5.2% of food energy. The proportion of food energy lost in nitrogenous excretion decreased with increasing ration. With increases in ration, the allocation of metabolizable energy to metabolism decreased, while that to growth increased. Fish size had no significant effect on the allocation of metabolizable energy to metabolism or growth. At the maximum ration, on average 64.9% of metabolizable energy was spent on metabolism, and 35.1% on

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00085.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A method is described for determining the expected reproductive success (gonadal mass of a returning fish times the probability of surviving to return) and expected fecundity of salmonids as a function of smolt size. Application of the method requires data relating (i) return weight and smolt size; (ii) probability of survival and smolt size; (iii) probability of return after one or two sea winters and smolt size; and (iv) gonads and return weight. Although there exists no published data set that contains all of this information, it is possible to piece together enough information from published sources on female Atlantic salmon to demonstrate the feasibility of the method, with the goal of encouraging the publication of datasets that will allow meaningful calculations for a single river. Thus, one should not expect general predictions about Atlantic salmon, but once local conditions are taken into account, it will be possible to predict the relationships between smolt size and expected fecundity or expected reproductive success.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb00086.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY