Fish abundance and trophic structure from the commercial catch in Lake Patzcuaro, Mexico

The composition, abundance and trophic structure of the fish community in Lake Patzcuaro is analyzed, using data from eight samples taken from the commercial fishery acquired between August 1990 and April 1991. A total of 65 767 individuals, caught with gillnets selective to all fish and size, were analyzed. Eleven species (8 native and 3 exotic) were recorded during the study. Zooplanktivorous were the most representative species, amounting to 91% of the total number. Also, they were the most characteristic species (36.4%) when feeding habits were considered, followed by carnivore and omnivore (27.3% each), and herbivore (9.1%). Three species groups and three time-associated groups were detected by means of classification methods. Lake Patzcuaro's ichthyofauna is to be considered as a transitional community that has not reached equilibrium, particularly after the introduction of exotic species and local extinction of native species. However, Lake Patzcuaro has the greatest fishery production of all tropical lakes in the Central Plain of Mexico and it is mainly sustained by native species. The differential use of feeding resources by the fish species and the diversity in their habits must be taken into account to design strategies to maintain the fish structure (avoiding new introduction of exotic species) and the fish production in Lake Patzcuaro.     

Retinoic Acid Is Involved in the Metamorphosis of the Anal Fin into an Intromittent Organ,the Gonopodium,in the Green Swordtail (Xiphophorus hellerii)

In poeciliid fish the male anal fin has been transformed into a gonopodium, an intromittent organ required for internal fertilization. Elevated testosterone levels induce metamorphosis of a subset of anal fin rays to grow and form the specialized terminal structures of the gonopodium. The molecular mechanisms underlying these processes are largely unknown. Here, we investigated whether retinoic acid (RA) signaling is involved in gonopodium development in the swordtail Xiphophorus hellerii. We showed that aldh1a2, a RA synthesizing enzyme, and the RA receptors, rar-ga and rar-gb, are expressed in anal fins during metamorphosis. aldh1a2 expression is regulated by testosterone in a concentration-dependent manner and is up-regulated in both hormone-induced and naturally developing gonopodia. Androgen receptor (ar), a putative regulator of gonopodial development, is co-expressed with aldh1a2 and the RA receptors in gonopodial rays. Importantly, experimental increase of RA signaling promoted growth of the gonopodium and increased the number of new segments. Based on gene expression analyses and pharmacological manipulation of gonopodium development, we show that the RA signaling pathway is activated in response to androgen signaling and promotes fin ray growth and development during the metamorphosis of the anal fin into the gonopodium.     

Microdontochromis rotundiventralis, a new cichlid fish (perciformes: Cichlidae) from Lake Tanganyika

Microdontochromis rotundiventralis, a new species of cichlid fish, is described on the basis of 13 specimens from Nkumbula Island, Lake Tanganyika (Zambia). It is distinct from its only congener,M. tenuidentatus, in having two (rarely one) rows of teeth on both jaws, a rounded distal margin on the pelvic fin, the outermost pelvic fin soft ray length 1.23–1.43 times the innermost ray, a deeper body (depth 26.8–29.1% standard length) and the anal fin with 9 (rarely 8 or 10) soft rays.     

中国鱼类科的新纪录——印度囊鳃鲇

作者在云南省盈江县采到鱼类标本44号,经鉴定为我国鱼类区系中科、属、种的首次纪录--印度囊鳃鲇(Heteropneustes fossillis)。     

Morphological variation in diadromous and landlocked populations of the spotted galaxias,Galaxias truttaceus,in Tasmania,south-eastern Australia

Synopsis A comparison of a suite of morphometric measurements and meristic counts of individuals of two landlocked lacustrine and two diadromous riverine populations of Galaxias truttaceus was carried out utilising both univariate and canonical variate analyses. Lacustrine fish had fewer dorsal and anal fin rays than did riverine fish. Differences were not as clear for gill rakers and vertebrae. Comparisons of serial counts were made with two derived lacustrine species, G. auratus and G. tanycephalus, also from Tasmania. Lacustrine G. truttaceus varied in the same direction as the derived species, relative to riverine G. truttaceus. From an analysis of 12 body measurements, the first canonical variate clearly separated lacustrine fish from riverine fish largely based on measurements associated with fins (pre-anal fin length, length of anal base, pre-dorsal fin length, maximum length of dorsal fin and inter-orbital width). An overall value for the correct classification of fish into groups based on locality was 84%. The percentage of fish classified into the wrong habitat (lake or stream) was much less than the percentage classified between localities within habitats. Overall morphological variation was greater between than within habitats. It is suggested that the differences in water movement and food type may in part account for the differences shown and that selective pressures peculiar to the lacustrine environment may be causing the lake populations to diverge from the riverine populations.     

Evolution of the elaborate male intromittent organ of Xiphophorus fishes

Internally fertilizing animals show a remarkable diversity in male genital morphology that is associated with sexual selection, and these traits are thought to be evolving particularly rapidly. Male fish in some internally fertilizing species have “gonopodia,” highly modified anal fins that are putatively important for sexual selection. However, our understanding of the evolution of genital diversity remains incomplete. Contrary to the prediction that male genital traits evolve more rapidly than other traits, here we show that gonopodial traits and other nongonopodial traits exhibit similar evolutionary rates of trait change and also follow similar evolutionary models in an iconic genus of poeciliid fish (Xiphophorus spp.). Furthermore, we find that both mating and nonmating natural selection mechanisms are unlikely to be driving the diverse Xiphophorus gonopodial morphology. Putative holdfast features of the male genital organ do not appear to be influenced by water flow, a candidate selective force in aquatic habitats. Additionally, interspecific divergence in gonopodial morphology is not significantly higher between sympatric species, than between allopatric species, suggesting that male genitals have not undergone reproductive character displacement. Slower rates of evolution in gonopodial traits compared with a subset of putatively sexually selected nongenital traits suggest that different selection mechanisms may be acting on the different trait types. Further investigations of this elaborate trait are imperative to determine whether it is ultimately an important driver of speciation.     

Anal‐fin ray morphology indicates sexual maturity in Brevimyrus niger (Teleostei,Mormyridae)

This osteological survey of 249 specimens of Brevimyrus niger ranging in size from 44 to 137 mm standard length (L_S) demonstrated that developmental changes in anal‐fin morphology can serve as a predictor of sexual maturity in this species. Anal‐fin ray bases begin to expand when fish reach c. 90 mm L_S at which size and above there were roughly equal numbers of individuals observed with expanded and unmodified anal‐fin bases, reflecting a 1:1 sex ratio.     

Genetic and morphological studies of Nothobranchius (Cyprinodontiformes) from Malawi with description of Nothobranchius wattersi sp. nov.

Molecular and morphological data were used to explore evolutionary differentiation among populations of Nothobranchius in the Lake Malawi–upper Shire River and the Lakes Chilwa–Chiuta drainage systems in Malawi. The aim of the study was to test the hypothesis that Nothobranchius of the Malawi–Shire system constitute a separate evolutionary group from Nothobranchius kirki. Mitochondrial and nuclear sequence data show a strongly supported phylogenetic split into two monophyletic groups separating the Lake Malawi basin fish from N. kirki. Unlike N. kirki, Lake Malawi–Shire fish do not deviate from neutrality and express an excess of rare haplotypes and mutations in terminal branches, characteristic of recently expanded populations. Further, the two groups significantly differ in morphology. Two body characters (dorsal‐fin base length and pre‐pelvic–pre‐anal distance) are significantly different between the two species in both sexes. Several other characters are significantly different in either male or female comparisons with respect to both standard and head lengths, and robust morphological differentiation is detected by multivariate analysis. The two groups are readily distinguished on the basis of male colouration, especially in scale centres and the caudal fin. On the basis of this differentiation at the molecular and morphological levels, in addition to colouration, the Lake Malawi–Shire fish are hereby formally recognized as constituting a new species, Nothobranchius wattersi. This distinction is in agreement with the geomorphologic and recent climatic history in the region.     

广西鱼类一新纪录:唐鱼(鲤形目:鲤科)

于2008年在广西一山涧小溪发现了国家Ⅱ级保护野生动物唐鱼(Tanichthys albonubes)种群,属、种均为广西新纪录.与广东从化野生唐鱼比较,广西唐鱼背鳍、腹鳍和臀鳍有明显黑色斑纹,尾柄较高,广西唐鱼种群在可量性状主成分分析上与广东从化唐鱼野生种群可以明显区分开来.我们还对唐鱼栖息地生境与环境进行了调查,栖...     

A new pearleye (Teleostei,Aulopiformes) species from the Oligocene of Romania

A new pearleye species of the alepisauroid family Scopelarchidae, Scopelarchoides neamticus sp. nov., is described herein based on two specimens from the Oligocene Lower Dysodilic Shales Formation, cropping out in the Pietricica Mountain, Romanian Eastern Carpathians. The new species described herein exhibits a unique combination of features (including head length about 25% of SL; coracoid remarkably expanded; both preorbital and postorbital lengths larger than orbit diameter; 50 or 51 vertebrae; dorsal fin with nine or ten rays; anal-fin with 28 rays; length of anal fin base about 30% of SL; preanal distance almost 60% of SL; pelvic fin insertion located just under the second dorsal fin ray; pectoral fins only slightly longer than pelvic fins; caudal fin with 19 principal rays plus 14 upper and 13 lower procurrent rays) that justifies its recognition as a new species of the genus Scopelarchoides. Both morphological and meristic features suggest a certain degree of similarity between S. neamticus sp. nov. and the extant species Scopelarchoides signifer. The fossils of the new Oligocene species described herein represent the oldest known skeletal record of Scopelarchidae.     

Testis and gonopodium development in Anableps Dowi (Pisces: Anablepidae) correlated with pituitary gonadotropic zone area

Testicular development in the viviparous fish, Anableps dowi, is described from embryonic stages through sexual maturation and is correlated with development of the gonadotropic zone of the pituitary. Only isolated spermatogonia or cysts of early spermatogonia are found in embryos 1.8 to 4.4 cm in length and postnatal specimens 5.4 to 8.8 cm in length. Cysts with more advanced spermatogonia are seen in specimens from 7.9 to 10.8 cm in length. Spermatogenetic meioses are first observed in a 10.2 cm male. Specimens greater than 12.0 cm have mature spermatozoa (partial spermatozeugmata) within the main testicular ducts, indicating gonadal maturation. The morphological transformation of the anal fin into the intromittent gonopodium is also described, using both whole and cleared specimens. Even in the smallest postnatal male available (5.4 cm), the anal fin can be distinguished from that of an equivalent sized female. Anal fin changes proceed until the mature gonopodium is developed, when body lengths greater than 16 cm are reached. Testicular maturation, defined as the presence of partial spermatozeugmata in the main testicular ducts, precedes the completion of gonopodial development. Measurements of ventral gonadotropic zone area in pituitary mid-sagittal sections show a continuous increase from neonatal through sexually mature specimens. The results point to a role for testicular androgens in early testis development.     

Cryobanking of fish somatic cells: optimizations of fin explant culture and fin cell cryopreservation

When gametes or embryos are not available, somatic cells should be considered for fish genome cryobanking of valuable or endangered fish. The objective of this work was to develop a method for fin explant culture with an assessed reliability, and to assess fin cells ability to cryopreservation. Anal fins from goldfish (Carassius auratus) were minced and gently loosened with collagenase before explants were plated at 20 degrees C in L-15 medium supplemented with fetal bovine serum and pH buffering additives. Quantification of cell-donor explants per fin rated the culture success. Cells were successfully obtained from every cultured anal fin (mean = 65% cell-donor explant per fin). All other fin types were suitable except the dorsal fin. Explant plating could be deferred 3 days from fin collecting. Fins from seven other fish species were successfully cultured with the method. After 2-3 weeks, sub-confluent fin cells from goldfish were cryopreserved. Cryopreservation with dimethyl sulfoxide and sucrose at a slow freezing rate allowed the recovery of half the goldfish fin cells. Cells displayed the same viability as fresh ones. 1,2-propanediol was unsuitable when a fast freezing rate was used. The procedure could now be considered for cryobanking with only minimal adaptation to each new species.     

A natural hybrid of Leuciscus cephalus (L.) and Chalcalburnus chalcoides (Güldenstädt)(Osteichthyes‐Cyprinidae) from Lake Tödürge (Sivas, Turkey)

Hybridization between Leuciscus cephalus and Chalcalburnus chalcoides was identified from biometrical features in 55 fish caught from Lake Tödürge, Sivas, Turkey, between April 1994 and November 1997. The hybrid index V _h for metric and meristic characters was intermediate ( V _h = 45·6) compared with their parents ( L. cephalus V _h = 0 or negative and C. chalcoides V _h ≥ 100). Morphological, metric and meristic features of L. cephalus  ×  C. chalcoides also resembled those of the parents. The majority presented an intermediate position which was best shown by the shape of mouth, caudal fin, gill rakers and pharyngeal teeth, and also by the caudal peduncle depth, head and interorbital width, predorsal and preanal distance, height of anal fin, length of anal base and other characters.     

Retention of loop,monel, and passive integrated transponder tags by wild,free‐ranging Lake Sturgeon (Acipenser fulvescens Rafinesque, 1817)

Tagging or marking of fish is instrumental to fisheries biologists and managers seeking to distinguish groups of fish, track movement or migration patterns, and monitor population characteristics. However, tag loss can inhibit the ability of biologists and managers to reach these objectives. The ability of Lake Sturgeon to live for long periods of time and reach large sizes, in combination with their dynamic spawning activity, requires tags to be retained under a variety of environmental and physically demanding conditions. This study evaluated tag retention of loop, monel, and passive integrated transponder (PIT) tags on wild, free‐ranging Lake Sturgeon in Lake Huron and the St. Clair – Detroit River System. Lake Sturgeon in this study were double‐tagged with both a PIT tag under one of the three anterior‐most dorsal scutes and an external tag (loop or monel) at the base of the dorsal fin. Fish were at large for up to 16 years. Overall, tag loss for PIT tags was 1% followed by monel tags at 12% and loop tags at 36%. Tag loss for loop tags was higher when the initial length of Lake Sturgeon tagged was smaller. Tag loss for monel tags increased with time at large but was not related to length at initial tagging. Monel tags left behind abrasion marks when attached to smaller Lake Sturgeon. PIT tag retention was higher than reported in previous studies that tagged other sturgeon species in different body locations. Monel tag retention was higher than other external tag types evaluated in previous studies while loop tags had similar retention rates to external tag types. Most previous studies on tag retention of sturgeon species were of shorter duration and conducted in laboratory settings, therefore loop tags may have performed more favorably during studies under short term laboratory settings. Results of this study suggest that PIT tags inserted below dorsal scutes represent a viable option for long‐term tracking of Lake Sturgeon. Monel tags attached at the base of the dorsal fin also seem to be a viable option relative to other external tag types, but should be limited to larger sturgeon as they can leave behind abrasion marks.     

Ontogenetic variation in fin ray segmentation between latitudinal populations of the medaka, <Emphasis Type="Italic">Oryzias latipes</Emphasis>

Fin rays of ray-finned fishes are composed of multiple bony segments, and each fin ray elongates by adding a new segment to the tip. Therefore, fin ray length is determined by the number of segments and the length of each segment. A comparison of the anal fin rays of a northern and southern wild population of the medaka, Oryzias latipes, revealed that southern fish had more segments per fin ray, resulting in longer anal fins than the northern fish. When fish were reared in a laboratory common environment, segmentation of the fin rays started earlier with respect to body size in the southern fish. In the southern males, moreover, the rate of segment addition accelerated after a certain body size, indicating sexual maturity. These patterns of segment addition during ontogeny were consistent with the patterns of fin ray elongation. Although distal segments tended to be longer, except for the most proximal segment, in both populations, the southern fish had shorter segments than the northern fish at any position on fin rays. These results indicate that the interpopulation variation in fin length is largely due to genetically-based differences in the control of segment addition, and that the length of each segment does not contribute to it. We suspect that fin ray segmentation is regulated by thyroid and sex hormones that differ between populations. We also found that some segments fuse with each other at the base of each fin ray, the functions and mechanisms of which remain unclear.     

Use of shape analysis in the investigation of disputable meristic characters for Ameiurus melas (Rafinesque, 1820) and Ameiurus nebulosus (Lesueur, 1819)

The aim of this paper was to use geometric morphometry as a helpful tool to clarify the overlap between meristic characters (such as the number of anal fin rays) of different fish identification keys employed for the two sister species, Ameiurus melas and Ameiurus nebulosus. Geometric morphometry included shape analysis of 15 landmarks on 432 specimens. The analyses showed significant differences among groups based on the sampling site, while there was no difference among groups based on the number of anal fin rays (used to distinguish species). This suggests that the use of meristic characters for the determination of these two sister species is rather questionable.     

Neolamprologus cancellatus, a new cichlid fish from Lake Tanganyika, Africa

Neolamprologus cancellatus, a new cichlid species, is described on the basis of eight specimens from the Zambian coast of Lake Tanganyika. The new species is characterized by a subtruncate caudal fin and a body that is slender (depth 22.3–25.2% in standard length) and easily distinguishable from its congeners by having 7–8 anal fin spines, 34–37 scales in longitudinal line, 33 total vertebrae, and a gridlike body pattern on a pale brownish body color. This species is only known to inhabit the shallow (2–7 m depth), rocky bottom of Wonzye Point in the southern part of the lake.     

The effects of relative density upon some aspects of the behaviour of the guppy—Poecilia reticulata (Peters)

Guppy populations were established as one sex or mixed sex groupings, relative degrees of population density were obtained by manipulating the numbers of fish or the volume of the living compartments. Relatively high densities resulted in a reduction in the males courtship behaviour, affecting the number of dorsal fin erections, gonopodial swings, numbers of black spots, number of sigmoid reactions and courtship chases. These measures reached a peak at populations of 12–16 fish/1, falling off both below and above these densities. Associated with a rising fish density was an increase in agonistic behaviour. Activity was not affected by increasing density. Increasing fish density was associated with a drop in the numbers of young fish born and the number of stages occurring within the ovaries. These numbers were greatest at a lower fish density than the behavioural measures.     

长江刀鲚不同生态型间的某些形态差异

摘要：为寻找和检验长江刀鲚（Coilia nasus）不同生态型间的形态差异,分析了江苏靖江、上海九段沙、浙江太湖和江西鄱阳湖4个种群906尾样本的脊椎骨数、臀鳍条数和上颌骨长。结果表明,即使是同一种群内的脊椎骨数和臀鳍条数变幅也较大,但均以靖江和九段沙种群的较多,众数分别为81、80和108、109;太湖和鄱阳湖种群...