Ocular morphology of the Baikal sculpin-oilfishes,Comephorus baicalensis and C. dybowskii (Comephoridae)

Synopsis Baikal sculpin-oilfishes (Comephorus baicalensis and C. dybowskii) were captured from Lake Baikal by mid-water trawl. External morphology was assessed using camera lucida drawings of whole heads. Retinal morphology was examined in material prepared for light and electron microscopy. A single rod-like photoreceptor is present in the retina, and this is at low density compared with marine species of similar depth distribution. C. baicalensis displays tubular eyes, with a dorsally displaced spherical lens and pupil, creating a dorsally directed visual axis. This corresponds to an area with a high density of photoreceptors in the ventral retina. Retinal structure is very similar in C. dybowskii with the exception that regional variation of cell densities within the retina is less marked than in C. baicalensis. In contrast to C. baicalensis, C. dybowskii has a caudal aphakic space and highest photoreceptor density in the rostral retina. Both species display changes in body attitude in association with diurnal vertical migration. We suggest that this may facilitate inspection of the water column from which predator strikes are most likely to occur. Comephorus in general display less specialization for vision in low light than marine counterparts with similar depth distributions.     

Lipids and fatty acids of two pelagic cottoid fishes (Comephorus spp) endemic to Lake Baikal

Matured females of two Lake Baikal endemic fish species, Comephorus baicalensis and Comephorus dybowski, have been investigated for lipid of the whole body and specific tissues (liver, muscles, ovaries), phospholipid classes and fatty acids of neutral and polar lipids. Total lipid in the body (38.9% fresh weight), liver (23.5%) and muscles (14.5%) of C. baicalensis were greater than those of C. dybowski (4.7, 8.7 and 2.6%, respectively); only their ovaries were similar (5.3 and 5.6% lipid, respectively). In both species, phosphatidylcholine and phosphatidylethanolamine were the major phospholipids, ranging from 60.7 to 75.1% of total phospholipid and 14.5–25.7%, respectively. In most cases, monounsaturated fatty acids (MUFA) were the major fatty acid group in C. baicalensis, whereas polyunsaturated fatty acids (PUFA) were the major group in C. dybowski. The MUFA 18:1(n-9) prevailed over other fatty acids in C. baicalensis and varied from 19% in polar lipids of muscles to 56.1% in neutral lipids of muscles. In polar lipid of C. dybowski, the PUFA 22:6(n-3) prevailed over other fatty acids in muscles and ovaries, while 16:0 dominated polar liver lipids and neutral lipids of all tissues. Other major fatty acids included 16:1(n-7), 18:1(n-7), and 20:5(n-3). Values of the (n-3)/(n-6) fatty acid ratio for neutral lipids of C. baicalensis (0.5–0.9) are well below the range of values characteristic either for marine or freshwater fish, while these values for polar lipids (1.6–1.8) are in the range typical of freshwater fish. Neutral lipid fatty acid ratios in C. dybowski (2.5–3.1) allow it to be assigned to freshwater fish, but polar lipids (2.8–3.7) leave it intermediary between freshwater and marine fish.     

Morphometry of the Gill Respiratory Area in Comephorus dybowskii and Some Other Endemic Cottoidei of Lake Baikal

Abstract Morphometric investigations of the gill apparatus in the small golomyanka, Comephorus dybowskii, revealed a unique structure and a very small gill respiratory area (GRSA) compared with other endemic Cottoidei of Lake Baikal: from 5.5 to about 7 times smaller than in the pelagic waterside sculpins. Cottocomephorus grewingki and C. inermis, and about 3 times smaller than in groundling deep-water Cotinella boulengeri. This is an extremely small GRSA considering no accessory respiratory organs are present. Scanning electron microscopic observations revealed numerous chloride cells in the epithelium of golomyanka gill lamellae but not in the sculpin lamellae. Chloride cells probably restrict gas exchange in the lamellae considerably. The results suggest that golomyankas have a small oxygen requirement.     

The evolutionary relationships of two families of cottoid fishes of Lake Baikal (East Siberia) as suggested by analysis of mitochondrial DNA

Fragments of mtDNA genes Cyt B, ATPase 6, and ATPase 8 of six cottoid fishes species of Lake Baikal (East Siberia) were amplified and sequenced. In addition mtDNAs of the same fish were subjected to restriction analysis. The data obtained were used to construct phylogenetic trees. The topology of the ATPase tree differs from those of the Res (restriction) and Cyt B trees. Clustering of species within the trees confirms the viewpoint of Taliev (1955, Baicalian Sculpins (Cottoidei)) according to which Baikalian cottoids originate from two ancestral forms. The times of branching obtained do not confirm the existing viewpoint according to which the two golomyankas (Comephorus baicalensis and Comephorus dybowskii) are pre-Baikal (Myocene) relicts: these two species may have originated 1.2–1.8 million years ago in Baikal, and they seem to represent an example of rapid morphological evolution which resulted in the formation of a new family. Correspondence to: S. Ja. Slobodyanuk     

Gill structure and morphometry of its respiratory components in the Baikalian golomyankas (Comephoridae; Cottoidei; Pisces)

All four pairs of gill arches in Comephorus baicalensis and C. dybowskii (Comephoridae) are well developed. In contrast to other Baikalian cottoids (Cottidae, Abyssocottidae), the slit behind the fourth arch is well preserved and two hemibranchs are present on this arch in the golomyankas. These anatomical details are considered to contradict the opinion that Comephoridae may be derived from other Baikalian Cottoidei. The arches in golomyankas are elongated and equipped with very strong spinous gill-rakers. The external sides of the upper and lower jaws are covered with numerous spinelike denticles, the apices of which are bent toward the mouth cavity. The denticles and the spinous gill-rakers are considered to be a specific adaptation in sluggish golomyankas for precise grasping of zooplankton of different sizes, as well as fish larvae. Respiratory components of the gill apparatus in the golomyankas are reduced considerably because of short gill filaments and the sparce distribution of small respiratory lamella on them. The allometry for the relationships between gill respiratory surface area (GRSA) and body mass (Y = aW^b) in both golomyankas is biphasic: in juvenile immature C. baicalensis Yj = 199.013 W^1.057 and in mature animals Ym = 322.354 W^0.731. In C. dybowskii the values for immature and mature animals are Yj = 95.736 W^1.190 and Ym = 199.609W^0.707, respectively. In the sluggish bathypelagic golomyankas (Comephorus) the GRSA per body weight unit is 5–6 times smaller than that found in more active secondarily pelagic Baikalian sculpins (Cottocomephorus) examined previously. © 1996 Wiley-Liss, Inc.     

Gill Respiratory Area in the Pelagic Sculpins of Lake Baikal,Cottocomephorus inermis and C. grewingki (Cottidae)

Morphometric investigations of the gill apparatus in the pelagic Baikal sculpins (Cottocomephorinae) reveal a relatively large gill respiratory area (GRSA). Allometric relationship between GRSA and body weight is expressed by the equation: Y = 746.61W^0.918 for C. inermis and that Y = 655.68W^0.913 for C. grewingki. In calculations per body weight unit the GRSA values C. inermis are a little higher than those in C. grewingki. Obtained numerical data seem to be in accordance with difference in biological activity of species examined. Their GRSA is several times larger than that in previously examined the bathypelagic Comephorus dybowskii and deep bottom dweller Cottinella boulengeri.     

The seasonal dynamics of Copidodiaptomus numidicus (Gurney, 1909) and Thermocyclops dybowskii (Lande, 1890) in Castelo-do-Bode Reservoir

We investigated the population dynamics of Copidodiaptomus numidicus (Copepoda: Calanoida) and Thermocyclops dybowskii (Copepoda: Cyclopoida) in Castelo-do-Bode Reservoir (Portugal). Both species in the reservoir were regulated mainly by food availability during the summers of 1993 and 1994. C. numidicus was always more abundant than T. dybowskii in the reservoir. C. numidicus produced two generations during the sampling period of both years whereas T. dybowskii produced two and three generations in 1993 and 1994, respectively. Because of high temperatures and low rainfall in 1994, the reservoir was more eutrophic than in 1993. Higher clutch size and a higher percentage of ovigerous females suggest that both species were benefiting from better feeding conditions in 1994. Despite this, population growth was reduced in 1994 relatively to 1993. Vertebrate predation and predation by copepods seem to have been minor factors in explaining this decline. However, the presence of Mesostoma sp. in the reservoir may have contributed to the reduction of both copepod populations during specific periods in 1994 although the calanoid was more affected than the cyclopoid by this predation.     

Rudd (Scardinius erythrophthalmus) introduced to the Iberian peninsula: feeding ecology in Lake Banyoles

The first data on the ecology of rudd (Scardinius erythrophthalmus) introduced to the Iberian peninsula are presented. The habitat and diet variation of rudd were studied in Lake Banyoles (Spain), an oligotrophic karstic lake dominated by exotic fish species. Rudd were strictly littoral and the diet was based on detritus and plant material. The most important animal prey were the cladocerans Daphnia longispinaand Scapholeberis rammneri, amphipods and several late stages of nematoceran dipterans. Rudd were more zooplanktivorous in spring and autumn and less in summer. There was also a size-dependent diet shift, from microcrustaceans to macroinvertebrates. The diet of rudd was also distinguished by the importance of plant material and various small neustonic invertebrates, particularly S. rammneriand late stages of nematocerans, showing a strong resource partitioning with other fish species. The degree of herbivory in Lake Banyoles was lower than usual.     

Amphipods on seaweeds: partners or pests?

Summary Herbivorous marine amphipods have been implicated as important grazers on filamentous and ephemeral algae, and thus as beneficial to macrophytes in reducing overgrowth by epiphytic competitors. In North Carolina, USA, amphipods comprise 97% of all macroscopic animals inhabiting the abundant brown seaweed Sargassum filipendula, and peak in abundance between late winter and early summer. I used outdoor tank experiments to test the species-specific impact of common phytal amphipods on the growth of Sargassum and its epiphytes. The results show that seaweed-associated amphipods are a trophically diverse group that could either increase or decrease host fitness depending on their feeding preferences. The amphipods Ampithoe marcuzii, Caprella penantis, and Jassa falcata each significantly reduced growth of epiphytes on Sargassum plants relative to amphipod-free controls, while Ericthonius brasiliensis had no significant effect on Sargassum or its epiphytes. However, amphipod grazing was not necessarily beneficial to Sargassum. A. marcuzii consumed Sargassum in one outdoor tank experiment, reducing its mass by 11%, while Sargassum plants without amphipods grew by 81%. Epiphytes (mostly diatoms and the filamentous brown alga Ectocarpus siliculosus) and detritus remained abundant on these plants suggesting that A. marcuzii preferred the host to its epiphytes. Similarly, when given simultaneous access to Sargassum and to several common foliose and filamentous epiphytes in the lab, A. marcuzii ate Sargassum almost exclusively. The other three amphipods ate no macroalgae. In contrast to A. marcuzii, C. penantis consistently reduced epiphytes with no negative effect on Sargassum. Thus the species composition of the amphipod fauna can determine whether these animals increase or decrease seaweed fitness.     

Diet of juvenile cod (age 0–2) in the Barents Sea in relation to food availability and cod growth

Diet investigations were carried out on 0-, 1- and 2-year-old Northeast Arctic cod (Gadus morhua) sampled in the Barents Sea during 1984–2002. Stomach-content analyses showed that the 0 and 1 group cod fed mainly on crustaceans, with krill and amphipods composing up to 70% of their diet. Krill (Thysanoessa spp. and Meganyctiphanes norvegica) and amphipods (Themisto spp.) were mainly found in cod stomachs sampled in the central and close to the Polar Front region in the Barents Sea where these prey organisms are reported to be abundant in summer. A shift in the main diet from crustaceans to fish was observed from age 1 to age 2. The diet of 2-year-old cod mainly comprised capelin (Mallotus villosus) and other fish, and to a lesser degree, krill and amphipods. Shrimp (mainly Pandalus spp.) was also an important prey in both age 1 and 2 cod. A statistically significant positive relationship was obtained between capelin stock size and the amount of capelin in the diet of 2-year-old cod. Results from this study also show that the larger age-2 cod preyed more on capelin in winter and that larger cod (>22 cm) prefer larger capelin (>12 cm). During periods of low capelin abundance, the 2-year-old cod shift their diet more to crustaceans, such as krill and amphipods. A positive significant relationship was also obtained between Total Fullness Index (TFI) and the amount of capelin in the diet and between TFI and the growth of 2-year-old cod, indicating that the growth of age-2 cod is to a large extent dependent on the amount of capelin consumed. Growth of age-1 cod was also positively correlated to TFI.     

Spawning-strategy-dependent diets in two North American populations of Atlantic salmon Salmo salar

The diet of repeat-spawner Atlantic salmon Salmo salar was investigated using carbon and nitrogen stable-isotope values from the outer growth band of scales, which reflect the fish's consumption and growth during their most recent marine phase. Isotope values for S. salar displaying different spawning strategies were compared between and within the Miramichi and Nashwaak Rivers, New Brunswick, Canada and a Bayesian mixing model was used to infer dietary contributions from potential prey items. Significant differences in the stable-isotope values were found among spawning strategies and between rivers, indicating differences in diet and feeding area, consistent with hypotheses. Bayesian mixing model results inferred the main prey items consumed during marine feeding by S. salar to consist of hyperiid amphipods and capelin Mallotus villosus for repeat alternate spawners from both rivers, sandlance Ammodytes sp. for repeat consecutive spawners from the Miramichi River and amphipods for repeat consecutive spawners from the Nashwaak River. These results demonstrate the diversity of feeding tactics among S. salar spawning strategies from the same river and between populations from different rivers. Accounting for differences in prey availability and the subsequent impact on S. salar diet and spawner return rates (i.e., marine survival) will facilitate the application of ecosystem-based management practices, such as ensuring that fisheries for forage species do not indirectly adversely affect S. salar return rates.     

Morphometry of gill respiratory area in the Baikalian deep-water sculpins Abyssocottus korotneffi and Cottinella boulengeri (Abyssocottidae,Cottoidei)

Abyssocottus korotneffi and Cottinella boulengeri are the deepest-living bottom species among freshwater teleosts. Both species have gill arches with nodulous gill-rakers equipped with sharp denticles. The gill-slit behind the fourth arch is reduced considerably and the hemibranch corresponding to this slit is absent, though some miniature structures resembling reduced filaments were occasionally observed there. The respiratory components of the gill apparatus in both species considered are much reduced, especially in A. korotneffi, because of the moderate number of relatively short gill filaments and the small number of respiratory lamella on them. The allometric relationship between the gill respiratory surface area (GRSA) and body mass (Y = aW^b) is expressed by Y = 328.55 W^0.724 for A. korotneffi (7–22 g) and by Y = 333.15 W^0.902 for C. boulengeri (3–24 g). In adult A. korotneffi, the GRSA index calculated per body weight unit is about 35% lower than that in C. boulengeri, but is 70% higher compared with the bathypelagic golomyanka Comephorus dybowskii previously examined. The data seem to correspond with the difference in biological activity of these species. J. Morphol. 233:105–112, 1997. © 1997 Wiley-Liss, Inc.     

A study of the intestinal microbiomes of the Lake Baikal oilfishes (Cottoidei,Comephoridae)

A comparative analysis of the intestinal microbiomes of some representatives of the Lake Baikal endemic family Comephoridae—the big oilfish Comephorus baicalensis (Pallas, 1776) and the little oilfish C. dybowski (Korotneff, 1904)—has been performed for the first time. The phylotype Akkermansia (phylum Verrucomicrobia) was detected in the C. dybowski microbiome, while Alistipes, Bacteroides, Chryseobacterium, Prevotella (Bacteroidetes), and Peptoniphilus (Firmicutes), were found in the C. baicalensis microbiome. Their presence in the intestine is associated with an elevated lipid uptake or an increase in the human and animal body weight. It is hypothesized that these microorganisms are involved in the lipid metabolism of the oilfish and determine their morphophysiological adaptations to pelagic life.     

Assessment of genetic stability of the germplasm lines of medicinal plant <Emphasis Type="Italic">Scutellaria baicalensis</Emphasis> Georgi (Huang-qin) in long-term,in vitro maintained cultures

An approach of combining flow cytometry (FCM) analysis with morphological and chemical profiling was used to assess the genetic stability and bioactive compound diversity in a Scutellaria baicalensis Georgi (Huang-qin) germplasm collection that was clonally maintained in in vitro for a period of over 6 years. Based on the FCM analysis of nuclei samples from young shoots, the nuclear DNA content of S. baicalensis was calculated as 0.84 pg/2C. FCM analysis showed no significant variation in the nuclear DNA contents and ploidy levels in the long-term in vitro maintained germplasm lines. Germplasm lines, acclimatized to ex vitro conditions, exhibited distinctive plant growth and bioactive compound production capacities. The high level of genetic stability observed in in vitro maintained S. baicalensis lines opens up a variety of opportunities such as allowing long-term aseptic preservation and easy distribution of well-characterized germplasm lines of this medicinal plant species. This study represents a novel approach for continuous maintenance, monitoring, and production of medicinal plant tissues with specific chemistry.     

贝加尔针茅响应降水变化敏感指标及关键阈值

降水是影响中国北方草原群落结构和生产力的关键环境因子,弄清植物响应降水变化敏感指标,确定关键阈值,可为草原的科学管理与制定应对气候变化措施提供依据。以贝加尔针茅为材料,基于不同降水的模拟实验,采用正态总体统计容忍区间及容忍限的估算方法,对测定的叶面积、株高、叶绿素和叶N含量等14个植物生理生态指标响应降水变化的敏感性及其阈值进行了研究。结果表明,植株总叶面积、水势(或叶绿素含量)和地上生物量可分别从形态、生理和生物量积累三方面较好地指示贝加尔针茅对降水变化的敏感性,受到胁迫时的降水量(6、7和8月3个月份总降水量)阈值分别是283、276(276)mm和280 mm。研究结果可为客观辨识贝加尔针茅草原干旱的发生发展与监测预警提供参考。     

Chick diet of dovekies Alle alle in Northwest Greenland

This paper reports the results of an investigation of dovekies (Alle alle) breeding at Hakluyt Island in the Thule District, Northwest Greenland. The paper presents a comprehensive examination of the chick diet of dovekies in the species' most important breeding area. Food delivered to nestlings consisted primarily of copepods Calanus hyperboreus and C. glacialis in the copepodite stages IV and V. Themisto libellula, other amphipods, decapods and fish larvae in small numbers were found in the chick diet. The zooplankton in the chick diet is presented both in terms of numbers and dry weight. The characteristic copepod of high-arctic waters, C. hyperboreus, was found to be the single most important species in the chick diet, contributing approximately 54% of the dry food weight. The food samples revealed low diversity, and the three species C. hyperboreus, C. glacialis and T. libellula made up 91.5% of the total zooplankton dry weight. The results from this paper are compared with previous dovekie-chick diet studies. Accepted: 14 June 2000     

Feeding habits of the speckled guitarfish Rhinobatos glaucostigma (Elasmobranchii: Rhinobatidae)

The stomachs of 464 speckled guitarfish Rhinobatos glaucostigma were sampled from the south‐eastern Gulf of California (GC) to determine diet composition. Numerical indices and prey‐specific index of relative importance (%I_PSIR) were used to determine the feeding strategy of the species. An analysis of similarity (ANOSIM) was used to determine differences in diet with respect to sex, season (dry or rainy) and maturity stages (immature or mature). The diversity and niche breadth (by sex, season and maturity) and a general trophic level were determined. The overall diet was dominated by shrimps (%I_PSIR = 43·47), amphipods (%I_PSIR = 18·89) and crabs (%I_PSIR = 18·07). ANOSIM demonstrated differences in the diet by maturity and season, but not by sex. Rainy and dry season diets were dominated by shrimps and amphipods, respectively. Immature specimens fed mainly on amphipods, whereas mature fish preferred shrimps and crabs. Rhinobatos glaucostigma showed a narrow niche breadth with an intermediary trophic level (T_L = 3·72) and can be considered as a secondary consumer in the soft‐bottom demersal community of the south‐east GC. Understanding the feeding habits and trophic level of R. glaucostigma is vital to help identify the segments of the population vulnerable to overfishing by artisanal and industrial fisheries, and to aid in conservation and management of this elasmobranch.     

不同水肥因子与AM真菌对黄芩生长和营养成分的交互效应

利用盆栽接种试验,探讨不同水肥条件下AM真菌双网无梗囊霉Acaulospora bireticulata对黄芩生长、养分含量和次生代谢产物的影响,为黄芩水肥合理施用提供理论依据。结果表明,不同水肥条件下,AM真菌能与黄芩根系形成良好共生关系,接种AM真菌能显著提高黄芩根系菌根侵染率和生物量,水分和施肥处理对菌根侵染率和黄芩生长具有显著交互作用。不同水肥条件下,接种AM真菌提高了植株保护酶活性和叶片渗透调节物质含量,降低了脯氨酸和丙二醛含量;显著增加了黄芩苷和N、P、K、Ca、Mg、Fe和Zn含量,降低了Mn和Cu含量。N和P含量随施肥量增加而提高,其余矿质元素在施肥量N 0.383 g、P 0.564 g、K 0.251 g时含量最高,说明AM真菌能够促进宿主植物根系对水分和矿质元素的吸收和利用,提高水分和肥料利用率,具有明显的节水节肥作用,其中50%相对含水量,施肥量N 0.383 g、P 0.564 g、K 0.251 g时,接种AM真菌的促生效应最佳。     

Feeding habits of juvenile <Emphasis Type="Italic">Trematomus newnesi</Emphasis> (Pisces,Nototheniidae) at Potter Cove,South Shetland Islands,Antarctica

The dietary composition of juvenile Trematomus newnesi, trawled at Potter Cove, South Shetland Islands, in the summers 2004–2005 and 2005–2006 was analysed using frequency of occurrence (F%) and dietary coefficient Q (%) methods. The samples consisted exclusively of immature specimens in the range 4–15.4 cm (total length) and are complementary to those of larger fish from the same site, including adults, which were analysed in previous work. Benthic-demersal organisms such as gammaridean amphipods and harpacticoid copepods were the main (coefficient Q) and most frequent (F%) prey. The importance of the smaller and larger main prey diminished and increased, respectively, during ontogeny. Pelagic krill, being negligible in the diet of the small and medium size fish categories, became secondary food, but only for fish larger than 12 cm. Other taxonomic groups occurred scarcely and constituted occasional food. They were mostly benthic, such as gastropods, bivalves, isopods, cumaceans, and algae, with the exception of an insignificant number of pelagic ostracods and calanoid copepods. Unlike the more pelagic/planktivorous mode of life known for late juvenile-adult stages of T. newnesi, including cryopelagy, present results indicate that early juvenile fish remain sheltered among macroalgae beds preying on the associated community of demersal-benthic organisms.