首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 203 毫秒
1.
Activities of pepsin, trypsin, chymotrypsin, alpha‐amylase and lipase, as well as their optima and stability to pH and temperature, were determined in digestive extracts of thick‐lipped grey mullet, Chelon labrosus, of three different sizes: Group 1 (45.2 ± 3.0 g), Group 2 (180.9 ± 4.2 g), and Group 3 (328.5 ± 43.3 g). SDS‐PAGE zymograms were also used to assess the role of serine proteases in the digestive tract of C. labrosus. On the other hand, possible changes in the digestive enzyme profile of C. labrosus during development were observed, with a comparatively lower pepsin activity, higher activities of alkaline proteases and alpha‐amylase and no lipase activity recorded in pre‐adult specimens. It is suggested that these variations are linked to the changes in diet composition with age, moving from a partly carnivorous to a more herbivorous feeding habit.  相似文献   

2.
The brackish Baltic Sea is inhabited by several primary freshwater fish species. The pike (Esox lucius) is the largest of these species and acts as the top predator in the marine food web of the Baltic Sea. Prior studies have shown the importance of brackish bays as spawning grounds for the Baltic Sea pike. To identify the spawning habitat of the pike population around the island of Rügen (southern Baltic Sea)—either freshwater streams flowing into the Baltic or brackish lagoons of the Baltic—we used the ICPMS method to quantify the strontium to calcium (Sr:Ca) ratios in sagittal otoliths of 79 adult pike. In total, only six per cent (n = 5) of the analysed Baltic Sea individuals were classified as being of freshwater origin. Ninety‐four per cent (n = 74) of analysed pike were classified as having hatched in brackish water. Compared to previous studies on Baltic Sea pike, our sample shows a high proportion of pike that is of brackish origin: this highlights the adaptive capacity of this species with regard to its ability to reproduce in different salinities. Our data highlight the importance of brackish bays for pike reproduction in the southern Baltic Sea, even if pike live on the upper limit of their salinity tolerance in this area. This is an important finding considering decreases in commercial catches in the last 30 years indicating a population decline supposedly related to recruitment failures.  相似文献   

3.
This work describes the ontogeny of the digestive tract in thick lipped grey mullet (Chelon labrosus) larvae reared until day 36 post-hatching with the semi-extensive technology in mesocosms. Diet was constituted by live preys, rotifers, Artemia and wild zooplankton, then compound diet was added from day 20 (p. h.). Linear growth, weight growth and digestive enzymes specific activities were studied during larval ontogeny. Pancreatic enzymes (trypsin and amylase) and intestinal enzymes (leucine-alanine peptidase “Leu-ala”, aminopeptidase N “AN” and alkaline phosphatase “AP”) were assayed in larvae sampled throughout the rearing trial to evaluate gastrointestinal maturation along the development.The trypsin specific activities were very high during the first two weeks and then declined as observed in marine fish species. A following increase in trypsin specific activity from day 20 was attributed notably to ingestion of particle compound diet. In contrast to the pattern generally described in fish larvae, amylase specific activity showed a continuous increase. This could be attributed to the fact that C. labrosus is an omnivorous species and suggests that the fish might be able to use efficiently diets containing higher levels of starch or other carbohydrates since the end of larval development.Relative expression of intestinal brush border membrane enzymes (AP and AN) and cytosolic enzyme (Leu-ala), showed an abrupt increase of both AP/leu-ala and AN/leu-ala ratios at day 8 (p. h.), indicating that maturation of intestinal tract in C. labrosus larvae is particularly precocious. It is assumed that larvae of C. labrosus might support early co-feeding and weaning strategies, which could reasonably be initiated since mouth opening.  相似文献   

4.
More than 1,000 age-identified chum salmon Oncorhynchus keta collected at 23 stations in the Bering Sea and the North Pacific Ocean in June to July 2003 were used to estimate their origin of stocks using a DNA microarray developed for analyzing the mitochondrial (mt)DNA haplotypes. The observed haplotype distribution was nearly the same as that reported previously for fish collected in September 2002 and 2003 in the present surveyed areas. A conditional maximum-likelihood method for estimation of stock compositions indicated that the Japanese stocks mainly distributed in north central Bering Sea, whereas the Russian stocks were mainly in western Bering Sea. The North American stocks were abundant in eastern Bering Sea and around the Aleutian Islands. Such an area-specific stock composition was not significantly different between mature and immature fish. Thus, the combined results of 2 years suggest that the distribution of chum salmon is nonrandom in the surveyed areas in summer and autumn, and that fish of the same origin migrate together to the same area irrespective of age.  相似文献   

5.
Eels (Anguilla spp.) are in decline worldwide, and the signs of reduced recruitment have been observed in continental Europe since the early 1970s. To aid recovery of the European eel, stocking is used by many European countries as a management option. In this study, tagging experiments were conducted to follow eel migration from Lake Mälaren and four sites along the Swedish east coast in the Baltic Sea. The recaptured tagged eels were retrieved from fishermen, allowing for the opportunity to investigate their origin (brackish water, stocked in freshwater or a mix in between) by otolith microchemistry and to assess for morphological differences after tagging. Several changes took place; for example, eye index increased while weight and condition decreased with migrated distance and time until recapture. In Lake Mälaren, the majority of tagged eels did not migrate out of the outlets, irrespective of their origin. Most of them were caught in the opposite direction and continued to be caught in the lake 1–3 years after tagging, with significant weight losses. Overall, overwintering is suggested to be an inferior option, but it is uncertain whether this is a natural behaviour or a result of translocation and restocking. For coastal eels, origin had no effect on migratory behaviour; a majority of the tagged eels migrated towards the outlet of the Baltic Sea. Interestingly, a minority of the recaptured eels originated from stocked fish. Instead, recaptures were dominated by natural immigrants that had spent most of their lives in brackish waters.  相似文献   

6.
This paper examines the changes in the population ecology parameters and biomass of golden grey mullet (Liza aurata) in Iranian waters of the Caspian Sea from 1991 to 2005. For most years during this 14-year period, we estimated the age structure of the catch, length–weight relationship, von Bertalanffy growth parameters, condition factor, natural and fishing mortality and biomass. Growth parameters were estimated as L∞ = 62.7 cm, K = 0.15 year−1, t0 = −0.23 year−1. The instantaneous coefficient of natural mortality was estimated as 0.350 year−1 and the instantaneous coefficient of fishing mortality varied during the 14-year period between 0.111 to 0.539 year−1. Biomass estimates of golden grey mullet, from the biomass-based cohort analysis were increased from 13,527 mt in 1991–1992 to 23,992 mt in 2002–2003. In 2004–2005, it was estimated to be 23,658 mt. We concluded that at the present time, the stock of golden grey mullet is not being over-fished.  相似文献   

7.
The life history of North American Atlantic salmon (Salmo salar) is characterized by extensive round‐trip migrations between freshwater rearing habitats and marine feeding grounds off the coasts of Canada and Greenland. Growth is rapid during the marine migration, and growth rate and condition factor may be indicators of salmon health during this period. Growth data were evaluated from a tag‐recovery program conducted from 1969 to 1991 using hatchery‐reared Atlantic salmon smolts released in the Penobscot River, Maine, U.S.A. Information from recaptures of 3167 salmon that were at large in the marine environment for 1 month to 3 yr was analyzed. Length–weight measurements coupled with time‐at‐large data were used to estimate von Bertalanffy and allometric growth parameters specific to the marine phase. Variations in growth and condition factor in relation to smolt age, release date, and temperature conditions in the northwest Atlantic were also examined. The von Bertalanffy k parameter declined with ordinal release date, indicating faster growth rates during the first year of smolts released earlier in the spring. The 2‐yr‐old smolts had a larger k than 1‐yr‐old smolts, although 1‐yr‐old smolts grew to a larger asymptotic size. Sea surface temperature had variable effects on growth parameters and condition factor, with temperature at the beginning of the migration and in overwintering habitat during the first year at sea having the greatest influence on length–weight relationships. Determining the mechanisms that influence growth of individuals during the marine phase will help elucidate the factors responsible for historic growth trends, establishing a baseline for current research.  相似文献   

8.
Abstract

Until 1990 the western Baltic Sea spring herring has been extensively used as raw material for the processing industry of the former German Democratic Republic. Today North Sea herring and other Atlantic herring stocks are preferred and utilization of the Baltic Sea herring stock, which has been caught between January and May around the Island of Rügen and in the Greifswalder Bodden, has dropped down dramatically. The reduction in exploitation of this resource is connected to enhanced quality specification required by German herring processing companies after reunion of both states.

In this study the quality of Baltic Sea spring herring from ICES subdivisions 22 and 24 was assessed and following conclusions were obtained:

  • Processing possibilities of Baltic Sea spring herring are limited due to low fat content (5-8%), a slight dry and short fiber texture and a less typical flavour and taste.

  • Off-flavour and taste (tainting) which has been often observed until mid nineties disappeared within the last years.

  • Infestation rates and abundance of nematodes (Anisakisspp.) are comparable to North Sea herring stocks.

  • Contamination levels of organic and inorganic pollutants are far below legal limits.

Only gill net fishery and trap fishing are able to guarantee a continuous supply of desired size classes 2 and 3. Trial with pair trawl fishing did not show promising results.

Due to reorganization and reduction of local fishery activities during the past ten years, an increase of the annual landing capacity of more than 10,000 t is questionable in future.  相似文献   

9.
Satellite telemetry from 26 loggerhead (Caretta caretta) and 10 olive ridley (Lepidochelys olivacea) sea turtles captured and released from pelagic longline fishing gear provided information on the turtles’ position and movement in the central North Pacific. These data together with environmental data from satellite remote sensing are used to describe the oceanic habitat used by these turtles. The results indicate that loggerheads travel westward, move seasonally north and south primarily through the region 28–40°N, and occupy sea surface temperatures (SST) of 15–25°C. Their dive depth distribution indicated that they spend 40% of their time at the surface and 90% of their time at depths <40 m. Loggerheads are found in association with fronts, eddies, and geostrophic currents. Specifically, the Transition Zone Chlorophyll Front (TZCF) and the southern edge of the Kuroshio Extension Current (KEC) appear to be important forage and migration habitats for loggerheads. In contrast, olive ridleys were found primarily south of loggerhead habitat in the region 8–31°N latitude, occupying warmer water with SSTs of 23–28°C. They have a deeper dive pattern than loggerheads, spending only 20% of their time at the surface and 60% shallower than 40 m. However, the three olive ridleys identified from genetics to be of western Pacific origin spent some time associated with major ocean currents, specifically the southern edge of the KEC, the North Equatorial Current (NEC), and the Equatorial Counter Current (ECC). These habitats were not used by any olive ridleys of eastern Pacific origin suggesting that olive ridleys from different populations may occupy different oceanic habitats.  相似文献   

10.
The Mugilidae family is an important fish group representing a major source for fisheries and aquaculture. In the south Mediterranean bank, no data are available on this fauna, except for some morphological studies on Tunisian samples. In this study, 16 allozymic loci were used to investigate the phylogenetic relationships within Tunisian mugilids. The results obtained from Hergla lagoon samples highlight five operational taxonomic unit corresponding to the well‐known species (Liza aurata, Liza ramada, Liza saliens, Chelon labrosus, Mugil cephalus). Several loci appeared to be diagnostic of these species, but in contrast to Greek mugilid samples, we did not find any diagnostic locus fixed differently for the five species. These results can help aquaculture units to identify accurately the mullet species they subsequently use for stocking aquaculture ponds and inland waters. However, species identity represents very important information, as each species has a different growth rate and salinity tolerance. On the other hand, when compared with North Mediterranean Mugilidae analysed until now, Tunisian samples show a genetic differentiation that could be related to different physicochemical conditions between the North and South banks, similar to those recorded in the eastern and western two Mediterranean basins separated by the Siculo‐Tunisian strait. In addition, this study confirms the morphological taxonomy, except for the subdivision of the Liza genus into two sub‐genera. The phylogenetic tree is in agreement with that on Languedoc Mugilidae samples (France), indicating that the subdivision of the Liza genus into two sub‐genera appears to be without any genetic base.  相似文献   

11.
The Baltic Sea is a unique ecosystem and the largest body of brackish water in the world. It is inhabited by several originally freshwater fish species, one of them being pike (Esox lucius), which is adapted to the mesohaline conditions of the southern Baltic Sea and colonises its south‐western bays and lagoons. Using twelve microsatellite markers, we analysed the genetic structure of 407 Baltic Sea pike collected from ten locations in the coastal zone of the southern Baltic region and adjacent rivers and nearby lakes. We used traditional F‐statistics and a Bayesian approach implemented in STRUCTURE to investigate spatial structuring. Our results show an overall isolation by distance pattern with two distinct coastal clusters. The border area between the two clusters is characterised by a sharp salinity leap, indicating that the dispersal barrier is not physical, but physiological in nature. A third cluster was formed by three lake populations, presumably as a result of past stocking measures. Additional otolith microchemical studies demonstrate the brackish origin and residency of the majority of the pike from the coastal lagoons, supporting previous studies which suggest that the anadromous pike “ecotype” is scarce in this area of the Baltic Sea. Our results contribute to current knowledge on the population genetics of Baltic Sea pike in a previously unsampled area.  相似文献   

12.
Hatcheries release >4.5 billion juvenile Pacific salmon (Oncorhynchus spp.) into the North Pacific Ocean annually, raising concerns about competition with wild salmon populations. We used retrospective scale analysis to investigate how the growth of chum salmon (O. keta) from western Alaska is affected by the abundance of chum salmon from Japanese hatcheries and wild pink salmon (O. gorbuscha) from the Russian Far East. Over nearly five decades, the growth of Kuskokwim River chum salmon was negatively correlated with the abundance of Japanese hatchery chum salmon after accounting for the effects of sex and spring/summer sea‐surface temperature in the Bering Sea. An effect of wild eastern Kamchatka pink salmon abundance on the growth of Kuskokwim River salmon was detectable but modest compared to the intraspecific competitive effect. A decrease in Japanese hatchery chum salmon releases in 2011–2013 was not associated with increased growth of Bering Sea chum salmon. However, the abundance of wild chum salmon from the Russian Far East increased during that time, possibly obscuring reduced competition with hatchery chum salmon. Our results support previous evidence that chum salmon are affected by intraspecific competition, and to a lesser extent interspecific competition, in the North Pacific, underscoring that the effects of salmon hatchery production transcend national boundaries.  相似文献   

13.
Grey mullet ponds situated in Arcachon Bay on the western Atlantic coast of France, display contrasting mixohaline habitats.The pattern of osmoregulation of Chelon labrosus and Liza ramada exhibiting differential penetration of fish ponds has been investigated. Key variables of salinity and temperature have been considered. The tolerances to low salinities and to fresh water have been determined. The dynamics of variation in plasma osmotic pressure and major plasma electrolytes (Na+, Cl?, K+) were studied in terms of: (1) gradual adaptation to a decreasing salinity gradient; (2) effects of a long-term adaptation in fresh water; (3) effects of low temperatures on sea water adapted fish.Both species can adapt to a wide range of salinities; however, while L. ramada show a good hypoosmotic regulation, with no alteration in plasma concentration over a wide range of salinity and after a long stay (5 months) in fresh water, C. labrosus cannot live for long periods of time in a wholly fresh water habitat. Both field samples obtained from thick-lipped grey mullets forced to stay in a freshwater pond and experimentally adapted fish showed, after 3 months, an unequivoqual decrease in plasma sodium and chloride, and plasma osmolality decreased to the same extent; this pattern of no compensation is bound, sooner or later, to end in death. The inability of C. labrosus to develop a long-term hypoosmoregulation in fresh water is referred to salinity preferences which probably limit the upstream penetration of this species.Plasma osmolality and major electrolytes (sodium and chloride) increased in cold (4 °C) sea water. This response might be due to a reduced ability of grey mullets to osmoregulate in cold waters. In the poly-mesohaline ponds, Winter drop in temperature (4–6 °C) causes grey mullets to migrate to the meso-oligohaline ponds where the mean temperature is more elevated (8 °C) and temperature changes less rapid (6–9 °C).  相似文献   

14.
Allometric growth and ontogeny were studied in thick‐lipped grey mullet Chelon labrosus reared in mesocosms from 1 to 71 day post hatching (dph). Multivariate allometric analysis of morphometric growth distinguished three distinct developmental stanzas separated by two morphometric metamorphosis lengths (Lm1 = 4.46 ± 0.06 mm; Lm2 = 28.56 ± 1.04 mm). Body mass growth also showed three distinct episodes separated by two inflections, correlated with morpho‐functional changes. First episode concerned pre‐flexion larvae and ended around 4.5 mm‐LT (14‐dph), coinciding with estimated Lm1. It was distinguished by reduced growth, but intense morphogenesis and differentiation processes. Organogenesis and allometric changes indicated that development priorities concerned feeding efficiency, by improving detection ability (sensory system development), ingestion capacity (head growth) and assimilation performance (digestive system differentiation), together with respiration efficiency (gill development). Second episode concerned post‐flexion larvae and, ended around 8.6 mm‐LT (25‐dph). It was distinguished by fast growth of trunk and tail, acquisition of adult axial muscle distribution and completion of gill filament development, improving locomotion and oxygenation performances. It corresponded to transition towards metamorphosing stage as indicated by later isometric growth, musculature maturation and acquisition of juvenile phenotype. Metamorphosis seemed to end at Lm2, suggesting to avoid zootechnic handling before this size.  相似文献   

15.
    相似文献   

16.
  • 1. The question as to whether no‐take zones, as reference areas in the Wadden Sea (eastern North Sea), may develop within a few years or decades towards an ecological situation similar to the one which may have existed in earlier times is examined.
  • 2. It is argued that the driving forces behind changes in species and habitats in the Wadden Sea are natural long‐term variability of abiotic factors and area‐wide anthropogenic impact (coastal engineering). 3. Fisheries in the Wadden Sea are shown to be of minor importance, and it is proposed that establishment of no‐take zones here will not result in the recovery and recolonization of missing species and habitats. The examples of species include European oysters (Ostrea edulis), sabellarian reefs (Sabellaria spinulosa) and white weed (Sertularia cupressina, Hydrallmania falcata).
Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

17.
Results from an acoustic telemetry study revealed for the first time a northerly migration route for Atlantic salmon (Salmo salar L.) smolts leaving the east coast of Ireland. Atlantic salmon smolts were tagged in spring 2019 in the Castletown and Boyne rivers. Three tagged smolts registered on disparate deep‐water offshore marine receivers as they travelled northwards out of the Irish Sea through the North Channel. One fish had migrated an estimated 250 km in a period of 32 days. The remaining two individuals were detected on receivers located off the Northern Ireland coast, further corroborating the northward migration of salmon smolts through the Irish Sea.  相似文献   

18.
We examined the formation of annuli by marginal observations on otoliths of gunnel (Pholis fangi) in the Yellow Sea to validate the age determination method and to derive the growth equation covering from larval to adult stages. Gunnels, ranging from 46 to 173 mm in total length, were collected by a bag net fishery from the western coastal waters off Korea from November 1998 to October 1999. Marginal observations indicated that the translucent zone (annual mark) on adult otolith was formed during the winter, whereas the opaque zone was formed during the summer. However, a translucent zone was formed between May and June in juvenile otoliths. This false ring was formed when the fish transited from the inshore pelagic life of larvae to the offshore bottom life of juveniles. The observed maximum age was 58 months. Using observed length-at-monthly age, growth in length was expressed by von Bertalanffy growth curve; Lt = 144.0 (1 − e−0.11 (t+0.43)). P. fangi spawned in winter recruit to inshore, and grow quickly in the nursery habitats in spring. Gunnel inhabit the bottom offshore area during the summer season, and reappear inshore thereafter.  相似文献   

19.
Goldfish (Carassius auratus) was one of the first fishes to be domesticated and has been widely introduced across the globe, but is now considered one of the world's worst invasive aquatic species. Surprisingly, there is a dearth of information on its spatial and temporal movement patterns, which hampers the development of effective control programmes. We examined the movement patterns of an introduced population of C. auratus in a south‐western Australian river using passive acoustic telemetry. The study population had a high residency index within the array (i.e. proportion of all days at liberty that, on average, each fish was detected by a receiver) with fish being detected on 64% of days. The individuals were also reasonably mobile, travelling a mean of 0.30 km (linear river kilometres).day‐1 within the array, and one fish moved 231.3 km over the 365‐day study period (including 5.4 km in a 24 hr period). Importantly, C. auratus displayed significant seasonal movement patterns including a clear shift in habitats during its breeding period with most mature individuals being detected in an off‐channel wetland during that time. The results of this study strongly suggest that C. auratus undertook a spawning migration into a lentic habitat. These results have important implications for developing control programmes for the species, such as targeting connections to off‐channel lentic systems during its breeding period.  相似文献   

20.
We examined the element pattern in the otoliths of a migratory fish species that inhabit the coastal areas in the brackish of the Baltic Sea. The northern pike (Esox lucius) show migratory behaviour, spawning in streams and rivers and foraging in the sea. We examined spawning migration in four nearby streams in the south‐west part of the Baltic. Otolith analysis by microPIXE revealed unique elemental patterns (Sr, Zn, Br, Co and Mn) for the juveniles in each of the different streams. The strontium signal in the otolith of the juveniles was used as an indicator of freshwater origin and the time spent in the stream. Adult pike in their migrating spawning phase were caught in each of the streams. The elemental composition in otoliths in their freshwater phase (using juvenile pike in the streams as references) was determined. A principal component analysis showed that the elemental fingerprint during the freshwater phase several years back in time was similar for the adult fish and for juveniles inhabiting the stream today. The results indicated natal homing of the adults to a specific stream, a conclusion that was strengthened by the fact that marked fish returned to spawn over consecutive years. Anadromous pike in the Baltic Sea may thus be divided in subpopulations. The results of the study may have implications for fishery management, as pike in the Baltic Sea cannot be seen as homogenous population.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号