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1.
From examination of the ratios of strontium to calcium laid down as a lifetime record in the otoliths of sea trout Salmo trutta from Gotland, Baltic Sea, it was found that: (1) the shortest stream was used mostly by precociously emigrant or coastally hatched spawners; (2) longer streams had more fish that underwent normal smoltification; (3) sea-caught fish were predominantly coastally hatched (presumably near stream mouths). Furthermore, some otoliths showed no evidence of a freshwater history at all, raising the possibility of a contingent of the coastal population that does not depend on riverine spawning. The results emphasize the importance of the coastal zone as natal and early life habitat for sea trout in the Baltic, particularly with respect to a potential change to a warmer climate which may exacerbate conditions within small, ephemeral trout streams.  相似文献
2.
Anadromous and resident forms of pond smelt, Hypomesus nipponensis, were found to occur in sympatry in Lake Ogawara, Japan. Profiles of Sr: Ca ratios from individuals could be grouped to two patterns (1) a resident pattern with low Sr: Ca ratios from core to edge and (2) an anadromous pattern with relatively low Sr: Ca ratios near the core with abrupt increases in ratios at a location approximately 0.3mm from the core. Spawners smaller than 60mm standard length (SL) were resident, between 60 to 80mm were mixed resident and anadromous, and larger than 80mm were anadromous. Anadromous individuals first migrated after 40 to 82 days from hatching (mean±sd, 59.1±13.5d) and 14.6 to 30.9mm SL (22.2±5.3mm). There was no difference in SL between resident and anadromous individuals during age at first migration, suggesting that size may not be the mechanism for divergence of alternative life history styles.  相似文献
3.
Otoliths of male (1+ year old) Terubok, tropical shad Tenualosa toli from the Lupar River, Sarawak, were treated in different ways to assess the effect of post-capture storage on element concentrations in the otolith core and edge detected by laser-ablation inductively coupled plasma mass spectrometry (ICPMS). Five treatments were compared: rapid removal and dry storage; fish kept 5 h after capture then otoliths removed; rapid removal and stored in alcohol; fish rozen for 24 h then otoliths removed; and storage of intact head in alcohol for several weeks. Seven elements were detected at the core and edge of otoliths (Li, Na, Mg, Mn, Co, Sr, Ba). Of these, Na, Mg, Co and Ba differed among treatments, being highest in treatments where the otolith remained in the head. Variation in element measurements due to treatment effects was similar to within-otolith variation for the other elements and was least variable in the fresh treatment. The variation in concentration between the core and edge was more significant than other sources of variation (up to 100 times) for some elements. These differences were probably due to physiological factors (ontogenetic) or to yearly changes in water chemistry. The results indicate that the method of otolith storage, especially freezing whole fish, can have a small, but measurable, effect on the concentrations of Na, Mg, Co and Ba.  相似文献
4.
Otolith Sr:Ca ratios were examined to evaluate the contribution of the stocked eel Anguilla anguilla elvers, which have been stocked in Lithuanian waters and mixed with naturally recruited eels for several decades, to the native eel population. Stocked eels were identified by the freshwater signature (Sr:Ca ratios <2·24 × 10−3) on the otolith after the glass eel stage. Naturally recruited eels, that had migrated through the North and Baltic Seas, were characterized by an extended seawater and brackish-water signature (Sr:Ca ratios >3·23 × 10−3) after the glass eel stage. Of 108 eels analysed, 21 eels had otolith Sr:Ca ratio profiles consistent with stocking while 87 showed patterns of natural recruitment. The ages of naturally recruited eels arriving in Lithuanian fresh waters varied from 1 to 10 years, with a mean ±  s.d . age of 5·2 ± 2·1 years. Eels from the inland Lake Baluošai were all freshwater residents of stocked origin. Stocked eels, however, accounted for only 20% of the eels from the Curonian Lagoon and 2% of eels sampled in Baltic coastal waters. This finding does not support the hypothesis that the eel fishery in the Curonian Lagoon depends mostly on stocking.  相似文献
5.
Sr : Ca ratios measured in the otoliths of sea‐caged Atlantic salmon Salmo salar showed distinct seasonal peaks that were unrelated to water temperature and somatic growth, suggesting other factors have a greater influence on strontium deposition. Atlantic salmon remained in the sea‐cages for two seasons, or equivalent to two‐seawinter fish in the wild and were subjected to seasonally varying temperatures. Water temperature appeared to be inversely related to the Sr : Ca ratios, but this relationship was statistically not significant. Furthermore, water temperature could not explain the distinct increase in the strontium during the second year. The intensity of the Sr peaks increased in the second season while average winter water temperatures were consistent between years. Additionally, strontium deposition in the otoliths was unrelated to somatic growth. Somatic growth, as evidenced by circuli spacings on the scales, was largely invariant and therefore could not explain the observed peaks. Though not explicitly measured, the data are consistent with the notion that strontium deposition is a function of maturity state in Atlantic salmon.  相似文献
6.
The timing of catches of anguillid glass eels and their otolith microstructure and microchemistry were studied in southwest Iceland, where the European eel, Anguilla anguilla and American eel, A. rostrata have been thought to live sympatrically, to learn about their early life history and the possible mechanism of the separation between these two species ranges. Catches at the site studied suggest that glass eels may have started upstream migration as the river temperature warmed in late June and early July. The glass eels were mitochondrially identified into two species, A. anguilla and A. rostrata, although the latter were likely hybrids between the two species based on a different study. Otolith analyses showed no sharp increases in otolith increment width or sharp decrease of otolith Sr:Ca ratio in either species, which are the characteristic changes corresponding to the onset of metamorphosis in many anguillid species including A. rostrata collected in North America and A. anguilla in Europe. The mean age at recruitment determined for the glass eels in Iceland were similar between the two species (336.6 ± 41.7 and 319.3 ± 36.0 days for A. anguilla and A. rostrata, respectively), as were their total lengths (range 58.0–78.5 mm and 58.5–73.0 mm). In addition, mean age at metamorphosis (278.0 ± 36.8 and 254.0 ± 47.7 days) and total age (372.3 ± 50.8 and 352.9 ± 42.6 days) were also similar between the two species. However, these ages of A. rostrata in Iceland were older than those in North America, and those of A. anguilla collected in Iceland were roughly intermediate between the rest of Europe and North Africa. These findings support the hypothesis that the timing of metamorphosis is a key factor for determining the place of recruitment of glass eels and maintaining the geographic separation between the two species.  相似文献
7.
This study examined the toxicological and physiological responses of a commercially important coral-reef grouper, Plectropomus leopardus (Serranidae), to injection of enriched stable-isotope barium chloride (BaCl2) solution. Thirty adult P. leopardus were subject to one of two 138BaCl2 injection treatment groups (corresponding to dosage rates of 2 and 4 mg 138Ba kg−1 body mass), and a control group in which fish were injected with 0·9% sodium chloride (NaCl) solution. Fish from each group were sampled at post-injection intervals of 48 h and 1, 3, 5 and 8 weeks, at which time blood and tissue samples were removed from each fish. Residual concentrations of Ba and 138Ba:137Ba ratios were measured in muscle, gonad, liver and bone tissues of each experimental fish. Elevated Ba concentrations were detected in all treatment fish tissue samples within 48 h post injection. Residual Ba concentrations decreased throughout the remainder of the 8 week experimental period in all tissues except bone. The BaCl2 injection had no significant effects on measured whole blood variables or on the plasma concentrations of steroid hormones. Enriched Ba stable isotopes can therefore be used at low dosages to mark larvae of commercially important marine fishes, without adverse effects on the health of the fishes or on humans who may consume them.  相似文献
8.
Temperate-zone anguillid eels use both saline (marine or brackish) and fresh waters during their continental phase, but use of fresh waters is paradoxical because on average these fishes grow more rapidly in saline than in fresh waters. Based on data from anguillid eels whose habitat-residency histories had been determined by Sr:Ca otolithometry, superiority of growth rates in saline water is much greater in American eels Anguilla rostrata in north-eastern North America (mean saline:fresh growth rate ratio 2·07) than in European Anguilla anguilla , Japanese Anguilla japonica and shortfinned Anguilla australis eels (range of mean ratios 1·12–1·14). Data from A. rostrata in the Hudson Estuary, U.S.A., and Prince Edward Island, Canada, were used to test adaptive explanations of catadromous migrations. The hypothesis that lower mortality in fresh water offsets faster growth in saline water was not supported because loss (mortality + emigration ) rates did not vary between saline and fresh zones of the Hudson Estuary. Hypotheses that anguillid eels move to fresh water to escape from larger anguillid eels in saline water or to evaluate habitat quality were not supported by size and age distributions. Catadromy in temperate-zone anguillid eels increases the diversity of occupied habitats and therefore lowers fitness variance caused by environmental fluctuations. Catadromy in temperate-zone anguillid eels could be due to natural selection for maximum geometric mean fitness which is sensitive to fitness variance. Temperate-zone catadromy might also be maladaptive, at least in local areas, due to shifts over time in selective pressures or to inability of panmictic genetic systems to adapt to local conditions.  相似文献
9.
Otolith chemical composition differed between juveniles of five fish species ( Solea solea , Solea senegalensis , Platichthys flesus , Diplodus vulgaris and Dicentrarchus labrax ) in nursery areas of six estuaries along the Portuguese coast (Douro, Ria de Aveiro, Mondego, Tejo, Sado and Mira). Spatially consistent patterns in the concentration of some elements were responsible for differences between species. Discrimination of estuaries using data from all species simultaneously averaged 44·7% of correctly classified cases, whilst discrimination of species averaged 76·2%. Moreover, species-related patterns in otolith fingerprints were highlighted when comparing species for each estuarine nursery area, with intra estuarine species discrimination averages ranging from 86·2 to 100·0%. Similarities in the otolith elemental fingerprints were larger between species with close phylogeny and ecology, particularly between flatfish and perciform species. In addition to the differences in physiological regulation of species, specific microhabitat use in a common environment was suggested as a relevant factor for the differentiation of otolith chemistry among species occurring in the same locations. Despite positive results in specific estuaries, variation in otolith composition limited the use of species as proxies to classify others to their system of origin.  相似文献
10.
The relationship between the strontium content of the outer layers of otoliths (an indication of recent marine, estuarine or riverine habitat use) and the strontium content of roe in ripe female brown trout Salmo trutta was examined in fish collected from the Pomahaka River and the lower reaches of the Clutha River, South Island, New Zealand. A close relationship was found between the strontium content of roe and the outer layers of otoliths. This finding suggests that spawned eggs collected from redds could potentially be used to track the extent of upstream spawning migrations by anadromous brown trout.  相似文献
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