摘要:

In order to better understand the basis for the acquisition of euryhalinity by juvenile salmon and the role of endogeneous stimuli, experiments have been carried out to examine the dynamics of ionic and acid‐base adjustments in fresh water (FW) and after direct transfer to full salinity (32 g l−1) sea water (SW) (1) on Atlantic salmon smolt during the natural period of smoltification in spring, (2) on presmolt salmon in autumn, after intraperitoneal implantation of pellets containing ovine growth hormone (oGH). During parr‐smolt transformation in FW, gill Na+/K+ATPase activity gradually rises, the plasma osmolality (Posm) is unaffected and the total CO2of the plasma decreases significantly while whole blood pH fluctuates slightly. Direct transfer of smolt from FW to SW provokes only a slight increase in Posm and emphasizes the acid‐base balance disruptions shown in FW. An oGHimplant in a presmolt stimulates gill Na+/K+ATPase activity in FW, and affects the acid‐base balance. After SW transfer (12 days after implantation), oGH treatment prevents the increase of osmotic pressure and the restoration of the acid‐base, ionic equilibrium was faster for oGH‐implanted fish than for sham‐operated fish. These observations show that in FW smelting salmon develop most of the systems they need for migration and growth in SW and that oGH implants induce the development of physiological characteristics of smolts in a non‐natural p

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01097.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Twenty‐one metazoan parasite species were found in Arctic charr at three coastal sites in west Greenland, includingNeascussp. and the nematodePseudoterranova decipiens, new records for Arctic charr. Twelve species are new records for Arctic charr in Greenland. The quantitative composition of the parasite communities varied, but the freshwater species (Diphyllobothrium ditremwn, Eubothriutn salvelini, Proteocephalus longicollis, Crepidostotnutn farianis) were usually numerically dominant, even in anadromous fish. The absence from Greenland of Mysidacea, Amphipoda, Ephemeroptera and Odonata excludes parasites requiring such organisms as intermediate hosts, including the cestodeCyathocephalus truncatus, nematodes of the genusCystidicola, and freshwater acanthocephalan

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01098.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Between‐population gene flow was estimated in neighbouring freshwater and anadromousSalmo truttapopulations from Asturias, Northern Spain. Populations from the same drainage showed a high mean level of gene flow. Gene flow was also found between populations from different drainages and was negatively related to the distance between river mouths. The strength of the homing orientation of migratory individuals (sea trout) is discusse

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01099.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A new method is described to estimate the survival of salmonids in streams from fertilization of the eggs to the emergence of the fry. The method is compared to other techniques generally used to estimate the egg‐to‐fry survival: fry traps, excavation of redds, construction of artificial redds and laboratory experiments. Especially designed boxes filled with substratum and freshly fertilized eggs are buried in the stream bed. Survival is determined at three different embryological development stages: eyed stage, hatching and emergence. Boxes are planted inside the stream bed using a special injector, so that substratum alterations are minimal around the boxes. This method was tested successfully in two different studies, one in Switzerland on the brown trout, the other one in Sweden on the sea tr

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01100.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The present paper studies the possibly different feeding strategies ofDiplodus sargusto crustaceans, molluscs, worms, and small fish. The buccal jaws are built strongly and bound together by numerous ligaments. The dentition is heterodont: incisors in front and molars in the middle and hind parts. The principal originality of the musculature of this species is the forward insertion of the adductores mandibulae. These are very thick and insert on both the upper and lower jaws, so that contraction of any individual muscle acts on the buccal pieces as a whole, which thus constitute a remarkable crushing device. The pharyngeal jaws are frail as in primitive perciforms: the lower ones are well separated, being bound only anteriorly, while the upper ones consist of the second and third pharyngobranchials and a posterior toothed plate. When feeding on crabs,Diplodus sargusalways sucks in the prey and seizes it with the buccal jaws. Mouth opening is accompanied by extensive protrusion of the mouth, with or without neurocranial elevation. Mouth sucking and seizing movements vary little. Once seized, the prey is usually moved to the molars and crushed. The crushing movements may be fast and ample or slow. In the latter case, deformation of the prey is observable. Crushing usually results in the crab being broken into pieces. The pharyngeal jaws grip one part of the prey and shift it to the oesophagus, then seize the second part.Diplodus sargusadapts its feeding behaviour to the type of prey. A snail, for instance, is crushed by the buccal or pharyngeal teeth, the pieces of shell are ejected, and the soft parts conveyed with difficulty to the oesophagus by the pharyngeal jaws. A fish on the other hand, is sucked tail first into the mouth cavity and quickly shifted to the digestive tract by the pharyngeal bones. Behaviour toward different prey differs by the presence or absence of parts of the sequence of feeding movements (for example crushing) or by the fact that certain movements or parts of the sequence are repeated. The variability of any movement in the sequence is the same whatever the sort of prey. Crushing occurs between the buccal incisors and molars and was observed twice between the pharyngeal teeth. Usually, it seems, the latter are involved in transport only. In transport, the left and right pharyngeal jaws may perform different functions: their movements, unlike the symmetrical movements of the buccal jaws, sometimes differ.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01101.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The response of female three‐spined sticklebacks (Gasterosteus aculeatus) to differences in food ration during the breeding season was quantified for several variables related to reproductive performance. The measured protein and lipid contents (mg g−1) of eggs were unaffected by ration. Egg size increased with an increase in both ration and female size, but the proportional increase in egg size was much smaller than the proportional increase in ration. The best predictor of mean batch (clutch) fecundity and weight was female size. There was a small but significant increase in batch fecundity with ration, but the increase was not directly proportional to the increase in ration. The rate of spawning, total breeding season fecundity and total weight of eggs spawned over the breeding season were sensitive to ration with breeding season fecundity and weight increasing in direct proportion to ration. Thus, in female sticklebacks, there is a hierarchy of sensitivity to ration in the response of variables related to reproduct

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01102.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The abundance, growth, spatial distribution, and feeding habits of five allopatric brook charr,Salvelinus fontinalis, populations (young‐of‐the‐year, 0+ juveniles; YOY) were compared with five other populations living sympatrically with white sucker,Catostomus commersoni. The study was made in oligotrophic lakes of the Laurentian Shield (Québec, Canada) during three sampling periods in 1989 (July, August and September). The abundance of YOY charr was significantly higher in allopatric than in sympatric populations (45·3 ± 3·8vs3·4 ± 3·8 fish/lake caught in 1773 m2of gillnets; P<0·005). The mean length of YOY charr did not differ among allopatric and sympatric populations at each sampling period; July: 60·2 ± 3·0vs60·0 ± 4·5 mm; August: 61·9 ± 4·5vs63·2 ± 4·1 mm; September: 77·9 ± 8·7vs77·3 ± 7·8 mm respectively. Horizontal distribution of allopatric YOY charr did not differ from that of sympatric charr, 65% of the fish being captured within the first 2 m depth and the rest between 2 and 7 m depth. In contrast, the vertical distribution of allopatric YOY charr from both communities was significantly different; 81% of allopatric charr were captured within 0·5 m from the substrate compared to 64% for sympatric charr (P<0·001). Differences in vertical distribution of the fish were related to differences in diet; allopatric charr fed mainly on benthic and large planktonic organisms whereas sympatric charr fed less on these organisms and more on terrestrial organisms. In the lake where YOY charr were most abundant, individuals were spatially segregated into two groups; one ‘littoral’, found in 0–2m depth, and one ‘profundal’, found in 3–6 m depth. Growth, condition, and feeding habits of charr from the two groups were differen

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01103.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Of 35 species collected from the shores of the Suez Canal and its lakes, five were abundant year round.Sihouettea aegyptiaandAphanius disparare of Red Sea (warm water) origin, whereasPomatoschistus marmoratus, Aphanius fasciatusandAtherina boyeriare Mediterranean species.S. aegyptiaandA. disparare distributed throughout the Suez system whereasA. fasciatusis restricted to the northern canal.P. marmoratusandA. boyerihave not spread southward beyond the Bitter Lakes. Salinity is the main limiting factor for the distribution of Mediterranean species.S. aegyptiaandA. disparare dominant in the Bitter Lakes (salinity 44‰), whereasP. marmoratusand A.boyeriare abundant in Timsah Lake (salinity 7·8–41·6‰). There was considerable interannual and monthly variation in the relative abundance of each species. The populations were dominated by a single age group, and life spans were no more than 2 years. Rapid growth was evident during the first spring inP. marmoratusandA. boyeriand during the first summer, early autumn inS. aegyptiaand A.dispar. The relative abundance of each food item in the diet varied with fish size and season.S. aegyptia, P. marmoratusand A.disparfed mostly on harpacticoid copepods, polychaetes, demersal eggs, diatoms and blue‐green algae whereas A.boyeri fedmostly on planktonic copepods. The warm water species are summer spawners, whereas the temperate species are autumn‐wint

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01104.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Data are presented from a 10‐year (1984 to 1993) study of aSalmo truttapopulation in the Afon Cwm, a small tributary of the Afon Dyfi, mid‐Wales. The stream is a spawning and nursery area for sea trout. Growth of trout within the stream can be summarized by a von Bertalanffy growth coefficient (K) of 0·310, with asymptotic length (1∞) 21·6 cm and with length at age 1 of 7·6 cm. Mean population density in the whole stream varied from year to year between 0·05 and 0·60 0‐group trout m−2and between 0·05 and 0·70 older trout m−2. Mean biomass varied, between years, from 0·1 to 3·5 g m−2for 0‐group and from 1·3 to 10·4g m−2for older trout. Loss between 3 and 5 months of age appeared to be proportionate at about 50 to 60% and instantaneous loss rate from 5 to 53 months of age varied from 0·04 to 0·10 month−1and was positively correlated with cohort number at 3 months of age. Production between 3 and 53 months of age varied between coho

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01105.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The distribution of vertebral fusions along the spinal column differed significantly among crosses from two hatchery stocks of coho salmon, indicating a genetic basis for this character.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1995.tb01106.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY