bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prey preferences of a riverine population of juvenile chinook salmon, Oncorhynchus tshawytscha
Authors: Sagar P. M. , Glova G. J. 
Published: January 2006

The diet of juvenile chinook salmon and the foods available to them were studied during spring and summer in a large, braided, New Zealand river. During both sampling periods fish and potential prey were collected at dawn and dusk. Analysis showed that in spring the feeding rate increased at dawn, when aquatic taxa comprised the majority of their prey. Prey of terrestrial origin dominated the diet at dusk in summer but formed only about 1% of the diet during spring, when few such prey were available.During spring the fish selectively preyed upon larger nymphs of the mayflies Deleatidium spp. However, in summer chironomids, other dipterans, and trichopterans were consumed to the exclusion of Deleatidium. Most of the chironomids and trichopterans taken were pupae or emerging adults and it is suggested that this may reflect differences in vulnerability during the diurnal emergence period.
Impact of acidification and eutrophication on the distribution of fish species in shallow and lentic soft waters of The Netherlands: an historical perspective
Authors: Leuven R. S. E. W. , Oyen F. G. F. 
Published: January 2006

The species richness and composition of fish assemblages were examined in lentic soft waters in The Netherlands. The selected bodies of water reflected a large variation in geomorphological and limnological factors. In total, 24 fish species were encountered in Dutch soft waters. During 1983–1984 Esox lucius, Perca fluviatilis, Rutilus rutilus, Scardinius erythrophthalmus, Tinca tinca and Umbra pygmaea were quite common. In slightly acid and alkaline waters (pH≥5) Rutilus rutilus, Scardinius erythrophthalmus, Perca fluviatilis, Ictalurus nebulosus and Cyprinus carpio accounted for about 90% of the total number of specimens in the catches. Strongly acid waters (pH < 5) generally were fishless. If fish were present in these waters, however, the catches mainly consisted of Umbra pygmaea. Only in a few strongly acid systems were other species collected. The lowest pH at which certain fish species occurred varied from 3.1 to 7.0. In particular, Umbra pygmaea was extremely acid‐tolerant. The percentage of waters which harboured fish as well as the average number offish species per water decreased steeply between pH 6 and 4.The sampled waters showed remarkable differences in their fish assemblages. With hierarchical classification, six groups of waters could be distinquished with respect to their fish fauna. The site groups are defined and characterized physico‐chemically and their fish assemblages described. Multivariate analysis showed that the structure of fish communities is strongly related to the pH, the alkalinity, trophic level and the ionic composition of the water. Comparison of historical and recent data on the occurrence of fish strongly indicated that in many sampling sites fish species or even entire fish assemblages had disappeared. Ordination of available data also illustrated recent changes in community structure. At least 67% of the nowadays extremely acid waters formerly harboured fish populations. The impoverishment of fish communities or the total loss of fish were primarily caused by cultural acidification. Limited nutrient enrichment of soft waters only resulted in minor alterations of fish assemblages.
The properties of tilapia sperm and its cryopreservation*
Authors: Chao Nai‐Hsien , Chao Wei‐Chung , Liu Kuo‐Chun , Liao I‐Chiu 
Published: January 2006

The specific differences between the testis, milt and sperm of six species of tilapia including Oreochromis aureus, O. mossambicus, O. niloticus, Tilapia zillii, O. nilolicus×O. aureus hybrid and red tilapia, Oreochromis sp., were studied. The shape of testis is tubular; the gonadosomatic index varied from 0.07 to 2.71. The pH values of individual milts ranged from 6.2 to 8.2 and the osmolarity from 240 to 380 mOsmol kg−1. The quantity of milt obtained by stripping averaged only about 0.3 ml, and only in the O. niloticus×O. aureus hybrid did it exceed 3 ml. Sperm motility graded from weak to moderate was determined for the stripped tilapia milt. Sperm concentrations ranged from 7.70 × 108 sperms ml−1 in T. zillii to 2.74 × 1010 sperms ml−1 in O. mossambicus. Tilapia sperm was active in various salinity ranges such as 0–5‰ for O. niloticus, and 0–15‰ for O. mossambicus and T. zillii. Extender containing 15% milk and 5% methanol was used to prepare milt mixture before cooling rapidly to −35° C and then at 5° C min−1 to −75° C for storage in liquid nitrogen (– 196° C).Fertility tests on frozen tilapia milt resulted in a fertilization rate of 72.7% (v. control 85.7%) for the 22‐day frozen milt of the O. nilolicus×O. aureus hybrid used to fertilize the eggs of O. honorum, and 93.4% (v. control 90%) for the 304‐day frozen sperm of red tilapia used to fertilize eggs of red tilapia.
Composition and ultrastructure of elasmobranch granulocytes. II. Rays (Rajiformes)
Authors: Hine P. M. , Wain J. M. 
Published: January 2006

The blood granulocyte composition of seven species of ray is given together with ultrastructural observations made on the epigonal organ and blood of Pavoraja spinifera and the spleen of a deepwater rajid skate. Under the light microscope three granulocyte types, eosinophils, eosinophilic granulocytes and neutrophilic granulocytes could be distinguished. At the EM level two granulocyte types were apparent, one with elongated granules containing longitudinal fibrils that consolidated to form an axial rod‐like inclusion, and the other with large, spherical, uniformly electron‐dense granules. Correlation of light and electron microscope observations indicated that the neutrophilic granulocytes with weakly basophilic, elongated granules become weakly eosinophilic, as eosinophilic granulocytes, and these in turn develop to eosinophils with granules containing axial rods. The other granulocyte type forms another population of eosinophils with spherical granules.The inter‐relationship of these granulocytes, the identification of eosinophilic granulocytes, or heterophils, as immature eosinophils, and the co‐existence of two morphologically distinct eosinophil forms are discussed.
The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds
Authors: Wright R. M. , Giles N. 
Published: January 2006

Yolk‐sac pike fry were stocked at densities of 0.74 – 81.4 m−2 in two ponds, each divided into eight sectors (mean area 155.8 m2). Growth and survival were recorded from May to December 1985. The growth rates were variable within each sector. The size‐range of sampled fish increased throughout the year, but showed no significant correlation with density. Fry survival was initially density‐independent but switched by late June/July to density‐dependence, ranging from 0.5 to 43.6% of initial stocking numbers. The highest mean daily mortality rates occurred during May‐July. The final survival in December ranged between sectors from 0.059 to 11.25% of the starting stock densities. The final biomass per unit area of pike surviving in December was not related to initial stocking density. In Pond 1 the mean biomass produced was 2.21 gm−2 and in Pond 2 was 3.49gm−2.Pike fry < 30 mm fed only on invertebrates; those 30–100 mm took a wide range of invertebrates, cyprinids. sticklebacks and other pike. Cannibalism occurred at most densities between 5.45 and 81.4 fish m−2.Where attempts are made to increase pike production in managed populations by releasing small fry, an upper stock density of 5 fry m−2 is advised if large, density‐dependent mortalities are to be avoided.
The effects of testosterone implants on ovarian morphology in the bluehead wrasse, Thalassoma bifasciatum (Bloch) (Teleostei: Labridae)
Authors: Kramer C. R. , Koulish S. , Bertacchi P. L. 
Published: January 2006

The effects of exogenous testosterone pellet implants at 21 and 40 days on the ovary of Thalassoma bifasciatum, a protogynous marine fish, are described. The characteristic markings of the terminal blue phase appeared by 4 to 5 days and were complete by 18 days. There was no shift in sex ratio in the treated fish when compared to an untreated control group. None of the ovaries showed signs of precocious transformation, i.e., spermatogenic tissue was lacking, and there was no evidence of duct formation. Instead, however, the ovaries of the treated fish showed marked degenerative changes characterized by oocyte breakdown, fat infiltration, vacuolization, the accumulation of fibrous PAS+ material and the appearance of small eosinophilic cells.These findings conflict with earlier studies on the same organism that employed different procedures. However, they resemble more closely the results obtained from work on another protogynoid, the ricefield eel, Monopterus albus. They add new light on the role of sex hormones in the reversal process of T. bifasciatum and hermaphroditic fishes in general.
Chromosome numbers, genome sizes, cell volumes and evolution of snake‐head fish (family Channidae)
Authors: Banerjee S. K. , Misra K. K. , Banerjee S. , Ray‐Chaudhuri S. P. 
Published: January 2006

Chromosome number, C‐value and cell volume studies were carried out on three species of the genus Channa, viz., C. punctatus, C. striatus and C. gachua. The chromosome number, karyotypic structure and DNA content per cell along with cell volume are reported and described. A series of chromosomal rearrangements are established in three different karyotypes along with polyploidy. Both pericentric inversion and Robertsonian fusion played a major role in chromosome rearrangements. The nuclear DNA content of these three species is within 19‐29% of the present‐day placental mammals, and is thus lower than the median amount for fishes in general and teleosts in particular. Their lower DNA content suggests that the three species of the family Channidae are highly specialized, and this is supported by their known morphologic, reproductive, behavioural and ecological characteristics.The evolutionary significance of these chromosomal rearrangements, their origin and their mode of establishment are discussed. A probable phylogenetic model based on karyotype, C‐value and chromosomal rearrangements of the genus is presented.
The importance of estuaries for sea‐bass, Dicentrarchus labrax (L.)
Authors: Kelley D. F. 
Published: January 2006

Information on estuary‐dependence of bass in U.K. waters is summarized from recent published reports and some unpublished data.There is substantial reliance on estuaries (including tidal backwaters with little freshwater inflow) such as the Hampshire harbours, in the first 4–5 years of life. Man‐related hazards to survival are considerable and increasing: they include destruction of or damage to habitats, losses of 0‐groups in power‐station intakes, and excessive unregulated fishing effort, mainly on 4–5‐year‐old bass. Some measures to protect bass in estuaries are now in hand, but much remains to be done.
The feeding relationships of the larger fish species in a Scottish sea loch
Authors: Hall S. J. , Raffaelli D. , Basford D. J. , Robertson M. R. , Fryer R. 
Published: January 2006

Patterns within a fish assemblage have been examined from catches obtained over a period of 17 months using fixed nets and rod and line sampling. A total of 19 species were caught with summer samples dominated by dab and saithe and winter samples by whiting. Cod were caught regularly throughout the year. Catches at the study site of dab and whiting occurred mainly at night but for cod and saithe catches occurred throughout the day. There was no indication ofa crepuscular or tidal rhythm for any species. Differences between our own observations and those from other published studies lead us to conclude that no species‐specific generalizations about feeding periodicities can be made. Feeding patterns are more likely to be determined by site‐specific features of particular habitats and their associated prey and predator assemblages.Examination of stomach contents data using a variety of methods indicates that conclusions are highly dependent on the form of the resource matrix used. However, our analyses indicate that during summer cod and dab feed on a much narrower range of prey than saithe and that there is significant overlap in their diets if a resource matrix based on percentage occurrence of prey species is used. Nevertheless, most diet overlap values for the species examined were low (between 0.1 and 0.2) suggesting that competition for food is unlikely. To date, no experiments have been performed to test the hypothesis that cod and dab compete for food.
X‐ray measurements of gill‐arch movements in filter‐feeding bream, Abramis brama (Cyprinidae)
Authors: Hoogenboezem W. , Sibbing F. A. , Osse J. W. M. , v.d. Boogaart J. G. M. , Lammens E. H. R. R. , Terlouw A. 
Published: January 2006

The technique of X‐ray cinematography was used to study pharyngeal movements in Abramis brama (L.). The theoretical and practical problems in X‐ray cinematography of feeding fish are discussed, as well as criteria for the selection of images suited for detailed measurements.Respiration and filter‐feeding on Daphnia pulex (length c. 1 mm) show different gill arch movement patterns in bream. Slits between gill‐arches are kept smaller during filter‐feeding. In addition, during filter‐feeding, this inter‐arch distance decreases considerably in a posterior direction. The hypothesis that particle retention occurs on the slits formed between adjacent gillarches and their gill‐rakers is not supported by the present results.
The influence of grass carp on habitat structure and its subsequent effect on the diet of tench
Authors: Petridis D. 
Published: January 2006

Ecological studies were carried out in shallow experimental sites in the Lancaster Canal to evaluate potential interactions between grass carp and feeding habits of tench.Grass carp, through moderate weed consumption, produced better conditions for the exploitation of benthic organisms by the benthophagous tench, because tench (>35 cm fork length) were able to search for food in the open areas created. This also enabled the fish to make use of zooplankton, mainly the large species Eurycercus lamellatus whose restricted phytophilic habitat made it vulnerable to predation. Epibenthic animals, in particular gastropods and Asellus aquaticus, suffered principally from the predation, which caused severe reduction of them in the site totally depleted of vegetation. In this site, tench utilized a diet in which red chironomids were the dominant prey group together with a large amount of fine detritus.It is suggested that a moderate control of vegetation in temperate climates, using the grass carp as the biological agent, could be a satisfactory management technique for the improvement of aquatic habitats.
Recruitment mechanism of the eel, Anguilla japonica, to the Japanese coast
Authors: Tukamoto K. 
Published: January 2006

A total of 149 Anguilla japonica elvers collected at 10 locations along the Japanese coast were aged according to otolith daily increments. The interrelationships among age, birth date, body size, pigmentation stage, sampling location and the timing of recruitment were examined in order to determine the recruitment mechanism of elvers to coastal waters.First catches of eels were earlier in the locations at lower latitudes. Age at recruitment was roughly constant, 218 ± 29 (mean ± s.d.) days old, disregarding the localities, but a weak positive correlation was obtained between age and sampling date or timing of recruitment. Body length at recruitment was also constant, 56.3 ± 2.3 mm s.l., and showed no significant correlation with either locality or recruitment timing. Estimated birth date ranged from April to November, the mean ± s.d. being 22 July 1982 ± 42 days, suggesting a peak season spawning in summer. Birth date was closely related with both the latitude of location and sampling time. Pigmentation developed more at lower latitude. Recruitment mechanism of the Japanese eel was summarized as follows: the earlier‐born individual recruits earlier at lower latitude and at younger age, but at a constant body size.
The impact of the introduction of Nile perch, Lates niloticus (L.) on the fisheries of Lake Victoria
Authors: Achieng A. P. 
Published: January 2006

The piscivorous Nile perch was introduced into Lake Victoria some 30 years ago, since when it has completely transformed the fishing industry and the species composition of the fish fauna of the lake. The original multispecies fishery, based mostly on cichlids (haplochromines, tilapias), cyprinids (Barbus, Labeo, Rastrineobola) and siluroids (Bagrus, Clarias, Synodontis, Schilbe), has changed dramatically to one based on three species: the introduced Nile perch, the cyprinids, Rastrineobola argenrea (Pellegrin), and the introduced Nile tilapia, Oreochromis niloticus (Linnaeus).Within 25 years of its introduction the Nile perch became ubiquitous and now occurs in virtually every habitat with the exception of swamps and affluent rivers. It has preyed on all other species with profound effects, especially on the stocks of haplochromines. These originally comprised 80% of the total fish biomass in Lake Victoria, but have now decreased to less than 1% offish catches from the Kenyan waters of the lake. The fishermen of Lake Victoria have adjusted to this ecological crisis by using large‐meshed nets to catch Nile perch, which has become the most important commercial species. For the first time in the history of Lake Victoria, fish fillets are now being exported to several overseas countries: the fillets are all from Nile perch.
The effect of humic substances on the toxicity of aluminium to adult rainbow trout, Oncorhynchus mykiss (Walbaum)
Authors: Witters H. E. , Van Puymbroeck S. , Vangenechten J. H. D. , Vanderborght O. L. J. 
Published: January 2006

Some physiological parameters were measured in adult rainbow trout during a 10‐day exposure to 180 μg Altotal l−1 in acid water (pH 4.7) with or without humic substances (10 mg l−). The fish were acclimatized to pH 5.0 for 7 days prior to the experimental treatments.Chemical analyses revealed that, in the presence of human substances, 74–80% of the A1 was organic bound, while in the absence of humic substances most of the Al(987percnt;) occurred in the inorganic form.Al bound to humic substances (13–150 μg l−1) did not alter the plasma NaCl‐concentration, nor the haematocrit value, of rainbow trout during an exposure period of 10 days. This contrasts with the high death rate obtained within 2–3 days when most of the A1 (175 μg l−1) was in the inorganic form. The lethality was accompanied by a 25% decrease in the plasmaconcentration of NaCl and a doubling of the haematocrit value. Bulk analysis revealed that when the metal was present in inorganic forms the total Al content of the gills (75 μg A1 g−1 wet weight) was 15 times higher than when it was present as bound to the humic substances. These experiments showed that the accumulation of A1 at the gills was accompanied by physiological disturbances, both being a function of the chemical speciation of Al.
Adrenergic responses and the Root effect in erythrocytes of freshwater fish
Authors: Cossins A. R. , Kilbey R. V. 
Published: January 2006

The effects of adrenergic‐stimulation upon the oxygen‐binding capacity of fish erythrocytes have been investigated. The oxygen capacity of rainbow trout, Oncorhynchus mykiss (Walbaum), erythrocytes was lowered by 44% on extracellular acidification (the so‐called ‘Root effect’). Addition of isoproterenol at 20° Ccaused an acid shift of the curve relating oxygen capacity to pH0 by approximately 0.2 pH units, a value which was similar to the change in intracellular pH caused by adrenergic stimulation (Cossins & Kilbey Journal of Experimental Biology, 148, 303–312, 1990). Moreover, when plotted as a function of pHi, the curves for control and adrenalinstimulated erythrocytes were superimposable suggesting that the adrenergic shift in the Root curve was a result of the change in pHi caused by activation of the adrenergic Na+/H+ exchanger.A similarly large adrenergic shift in the Root curve was observed for pike, Esox lucius L., erythrocytes, though not for erythrocytes of carp, Cyprinus carpio L., and tench, Tinea tinea (L.). The pH for the mid‐point of the Root effect in pike erythrocytes was distinctly more acid than for trout, but in both cases corresponded closely with the optimal pH for the adrenergic Na+/H+ exchange mechanism. This suggests a link between the functional characteristics of the exchanger and the oxygen‐binding properties of haemoglobin.
Mechanisms of aluminium extraction and accumulation at the gills of rainbow trout, Oncorhynchus mykiss (Walbaum), in acidic soft water
Authors: Playle R. C. , Wood C. M. 
Published: January 2006

Rainbow trout were fitted with latex masks for the measurement of ventilatory flow rate (V̇w) and with opercular catheters for sampling expired water from close to the branchial surface. Fish were exposed for 6 h to pH 5.1, 4.7 or 4.1 in the presence (138 μg l 1) or nominal absence (1 μg 1–1) of Al. Inspired and expired Al concentrations and water pH were measured via the opercular catheters. Gills were sampled for accumulated Al at the end of the experiments. V̇w increased during Al exposures at all three pHs. However, in the absence of Al, V̇w increased only at pH 4.1. Aluminium extraction from the water and Al accumulation on the gills were highest at inspired pH 5.1 and lowest at pH 4.1, and correlated well with expired pH, which was 0.2–0.7 pH units higher than inspired pH. Gill Al accumulations amounted to only about one‐tenth of deposition calculated from Al extraction from the water and V̇w, and gill Al was tightly bound to the branchial surface.Calculations of Al solubility, oversaturation, and species composition were made using measured expired pH values, and were compared with Al extraction from the water and measured gill Al concentrations. In general, these analyses indicated that reduced Al solubility near the gills is a reasonable explanation of Al extraction from the water, and that Al(OH)2+ and Al(OH)3° are the Al species most likely to interact initially at the gills. It is suggested that mucus sloughing removes most precipitated Al, and that only the charged form persists, bound to structural elements on the gill surface. A model incorporating these results, and pH changes in the fish gill micro‐environment in general, is presented to explain previously‐reported ionoregulatory and respiratory effects of Al.
A comparison of circatidal rhythmicity and entrainment by hydrostatic pressure cycles in the rock goby, Gobius paganellus L. and the shanny, Lipophrys pholis (L.)
Authors: Northcott S. J. 
Published: January 2006

The intertidal teleosts Gobius paganellus and Lipophrys pholis show endogenous circatidal activity rhythms when recorded in constant conditions. Under these conditions, the rhythm of L. pholis is the more precise which may indicate stronger coupling between underlying circalunadian oscillators in this species. In G. pagunellus the inter‐oscillator coupling may be weaker and this could enable a more subtle interpretation of tidal fluctuations than in L. pholis. The oscillators may, however, be fundamentally different in the two species; circalunadian in G. paganellus and circatidal in L. pholis.When exposed to hydrostatic pressure cycles of tidal frequency both species responded pre‐ dominantly to increasing pressure, which suggests that in the wild they are likely to be most active on the rising tide. Hydrostatic pressure cycles are confirmed as a zeitgeber for both species by the successful entrainment of some individuals. The lack of entrainment of others impIies that additional zeitgebers are required for complete entrainment.