摘要:

Mirogrex terraesanctae(Steinitz), is an endemic, open water, zooplanktivorous fish. It spawns in the shallow littoral (0–50 cm) of Lake Kinneret, from November to May with a peak in mid winter (January‐February). Spawning begins shortly after nightfall, when schools of the fish move along the shoreline in rocky regions, and release their milt and eggs. The adhesive eggs are attached to the surface of recently inundated, algae‐free stones. A negative relationship exists between epilithic growth and egg density and survival. Algal growth may play a key role in the determination of the spawning depth. Breeding success ofM. terraesanctaedepends on the rate and extent of rise in lake level which, in turn, determines the availability of a suitable spawning subst

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02715.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Muscle proteins were investigated in two large European barbels,Barbus barbusandB. meridionalis, and in four small tropical barbels native to SE Asia:B. conchonius,B. tetrazona,B. sachsiandB. titteya. Polyacrylamide gel electrophoresis was used to analyse myosin heavy and light chains and parvalbumin isotypes from white trunk muscle. Each species could be biochemically identified. The myosin subunit and parvalbumin isotype patterns obtained for the two European barbels were similar. The Asian barbels, on the other hand, not only differed from the European species but displayed a greater diversity within their group. These biochemical results are largely in agreement with morphological and genetic data, but fail to substantiate suggested close relationships between Asian barbel species.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02716.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Egg size forFundulus heteroclitus(L.) populations is concordant with the distribution of the twoF.heteroclitussubspecies, i.e.F. h. heteroclituseggs are considerably larger thanF. h. macrolepidotuseggs. The influence of egg size on survival of embryos during incubation and survival and growth of newly‐hatched larvae was estimated for four populations representing both subspecies along the Atlantic coast of the United States and in Delaware Bay. Survival of embryos was determined for incubation periods of 14, 21 and 28 days. Greatest differences in survival were detected following the longest incubation period where less than 50 per cent of the smallerF. h. macrolepidotuseggs survived while little or no mortality was detected among the largerF. h. heteroclitus eggs. Influence of egg size on larval survival was also greatest among those larvae hatched after 28 days whereF. h. macrolepidotuslarvae survived without food, for an average of 6 days, whileF. h. heteroclituslarvae survived 11–12 days.F. h. heteroclituslarvae were significantly larger at hatching thanF. h. macrolepidotuslarvae. Larval growth rates were the same (0.4 mm day−1) in both subspecies. As a result, size differences at hatching were still maintained after 42 days of growth. The differences in egg size along with other morphological and reproductive characteristics ofF. heteroclituspopulations probably represent genetically based adaptations to environmental conditions, of which the length of the spawning season is one of the major components stimulating the coevolution of these t

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02717.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A standard method comprising multi‐mesh monofilament nylon gillnets and depth stratification, the Drottningholm method, was employed in test fishing of a small Zambian reservoir (32 ha) on eight occasions over 1 year. The catch per unit effort (cpue) from the 0–3 and 3–6 m zone was timated with benthic and pelagic nets, while in the 6–12 m zone only benthic nets were used. Results include species caught and cpue with coefficients of variation and confidence intervals, for net types and depth zones. A total of 11 species were caught, of whichBurbus paludinosus,B. marequensis,Laheo cylindricus, andOreochromissp. dominated. Coefficients of variation did not indicate a preferable season for test fishing. During the cold season some species were not caught. The applicability of the method in estimation of species composition and cpue is di

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02718.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The trophic and spatial interrelationships between a native (Galaxias vulgurisStokell, Galaxiidae) and an exotic (Salmo truttaL., Salmonidae) fish species were investigated over a 24‐h period in a New Zealand stream. Interspecific overlap in feeding was greatest at dusk and dawn, as G.vulgarisfed primarily from dusk to post‐dawn andS. truttafed primarily from pre‐dawn to post‐dusk. Both species fed mainly on benthic and drifting aquatic invertebrates, with larvalDeleatidium(Ephemeroptera).Hydora(Coleoptera) and Chironomidae (Diptera) being their preferred prey, although Trichoptera imagos were also preferred byS. trutta. Both species were found primarily in runs and riffles withG. vulgarisoccupying slightly shallower (≤0.3 m) and faster (0.3–0.7 m s1) waters than didS. trutta(≤0.5 m deep and 0.2–0.4 m s−1water velocity). We suggest that these rather subtle interspecifc differences in die1 feeding periodicities, diets and microdistributions play a part in lessening the interaction between co‐occurring populations ofG.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02719.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The behavioural thermoregulation of Atlantic codGadus morhuaL. was investigated in a shuttlebox at normoxia and at three levels of hypoxia: 30, 20 and 15% oxygen saturation.The preferred temperatures at normoxia, 30, 20 and 15% oxygen saturation were 13·9, 13·1. 10·0 and 8·8° C, respectively.A decrease in metabolism and an increased blood oxygen affinity are among the physiological advantages of selecting a lower temperature during hypoxia. Furthermore the chances of surviving low oxygen saturations are better at low temperatures.In natural environments, this behaviour may result in habitat shifts of fish living in heterothermal environments with changing oxygen saturations, especially in coastal areas with eutrophication, as for example the Baltic

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02720.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Fish eggs and larvae were collected monthly between September 1987 and April 1989 from sites throughout the main basin and within the saline regions of the two main tributary rivers of Wilson Inlet, a seasonally closed estuary in south‐western Australia. Of the eggs, 43.7% belonged toEngraulis australis(Shaw) and the rest to unidentified teleosts. The larval fish assemblage comprised 17 families represented by 25 species. The Gobiidae contained the highest number of species (four) and contributed approximately 57% of all larvae caught.Pseudogobius olorum(Sauvage) andE. australiswere the most abundant species, contributing 43.9 and 27.9% to the total larval catch, respectively. The larvae of species which breed within Wilson Inlet dominated the assemblage, both in terms of number of species (64%) and contribution to total catch (99.9%). The numbers of the eight marine species and one freshwater species represented in the ichthyoplankton were very low. Classification and multi‐dimensional scaling ordination showed that the composition of the larval fish fauna at the various sites during a period when the estuary remained open to the sea (December 1988‐April 1989) was similar to that of the corresponding sites during the same period in the previous year when the estuary had become closed (December 1987‐April 1988). This can be attributed to the spatial distribution, time of occurrence and abundance of estuarine‐spawned larvae being similar in the two periods and to the rarity of marine‐spawned larvae, even in the spring and summer of 1988/1989 when the estuary was open for the whole time when most marine teleosts spawn in south‐western Australia. The low occurrence of marine‐spawned larvae in Wilson Inlet reflects the fact that tidal water movement within the basin of the system is so small that it is unable to facilitate the transport and dispersion of larvae. The ichthyoplankton of Wilson Inlet resembles that of other poorly‐flushed estuaries in that it is low in species richness and dominated by estuari

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02721.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Recent studies have demonstrated that Arctic charr (Salvelinus alpinus) exhibit higher growth rates when held at high stocking densities. It has been argued that these increased growth rates are a result of decreased social interactions at the increased densities. The current study was designed to test this hypothesis by examining: (1) the frequency of agonistic interactions, (2) the proportion of time spent swimming and (3) growth rates among groups of young of the year Arctic charr held at different stocking densities. It was found that charr reared at higher densities exhibited significantly higher mean weights and lengths than those at the lower densities. The behavioural observations revealed that charr initiated significantly fewer agonistic interactions and spent a significantly greater amount of time shoaling at high densities than charr held at the medium or low densities. It is argued that these behavioural responses may serve to lower energy expenditures, resulting in the increased growth rates.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02722.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The cyclic pattern of oocyte development in the sea bass,Dicentrarchus labraxL., was studied after induction of spawning by two injections, 24 h apart, of a luteinizing hormone releasing‐hormone analog (LHRHa) administered at the end of vitellogenesis. The first difference in the developmental stage of the ovary and in the size‐frequency distribution of oocytes between the LHRHa treated group and the control group, was detected 32 h after the first injection, the LHRHa group showing a higher proportion of the 900 μm diameter oocyte class (maturing oocytes) (P<0.01). At 48 h LHRHa‐treated females showed an increase in the 1000 and 1100 μm classes (maturing oocyte and ovulated eggs) (P<0.01) and at 72 h these females exhibited a bimodal pattern, reaching the highest proportions in the 1100 (27.4%) and the 600 (14.7%) μm classes (ovulated eggs and advanced vitellogenic oocytes, respectively). Bimodal distributions were present in 80% of the LHRHa‐treated females. Once oocyte final maturation was triggered by LHRHa the time needed for ovulation was about 48 h and the interval between consecutive ovulations and spawnings seemed to

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02723.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Characteristics of the reproductive cycle ofBasilichthys microlepidotus(Jenyns), an atherinid fish living in a South American Mediterranean arid zone, are analysed. Specimens 9‐170 mm in total length were captured from August 1982 to April 1984 in the Rio Choapa, in northern Chile (31%%45′ S, 71°15′ W). Analysis of gonadosomatic index fluctuations, and determination of the proportion of mature males and females captured during the study period, allowed the estimation of the duration of the reproductive cycle.Females 70–170 mm in total length contained 2000–9000 intraovarian oocytes, of which approximately 80% were vitellogenic (100–1300 μm in diameter) and exhibited a polymodal distribution. A further 4 to 15% of the total oocytes, measured 1700–2000 μm in diameter and appeared ready to be spawned. In 30% of the examined ovaries some of the largest oocytes exhibited signs of degeneration, or atresia. Juveniles approximately 30 mm in total length were captured over most of the study period. Results strongly suggest thatB. microlepidotushas mu

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1992.tb02724.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY