Reproduction in Odontesthes bonariensis (Atherinidae: Pisces) from north-western Argentina

The spawning biology of silver fish, Odontesthes bonariensis (Cuvier and Valenciennes 1835), from north-western Argentina was studied from monthly captures between November 1997 and March 1999. The spawning period and lengths thereof were analysed using gonadosomatic index (GSI) curves and monthly percentage distributions of maturation stages. A single spawning season with two peaks (late winter and early autumn) within 1 year was identified. Also discussed is the relationship between GSI and Fulton's condition factor K.     

Acanthocephalan infections in Atherina boyeri (Pisces: Atherinidae) from Tirso.

Infections by the acanthocephalan Telosentis exiguus (Von Linstow, 1901) and another unknown acanthocephalan were studied in the sand smelt Atherina boyeri (Risso, 1810) from the Tirso River mouth in Sardinia. Only a few specimens of T. exiguus (1 male and 2 cystacanths) were found in the host digestive tract; some larvae of an unidentified acanthocephalan encysted in the liver of A. boyeri were also found and are described.     

Multilocus phylogenetic analysis of the genus Atherina (Pisces: Atherinidae)

Sand-smelts are small fishes inhabiting inshore, brackish and freshwater environments and with a distribution in the eastern Atlantic and Mediterranean Sea, extending south into the Indian Ocean. Here, we present a broad phylogenetic analysis of the genus Atherina using three mitochondrial (control region, 12S and 16S) and two nuclear markers (rhodopsin and 2nd intron of S7). Phylogenetic analyses fully support the monophyly of the genus. Two anti-tropical clades were identified, separating the South African Atherina breviceps from the north-eastern Atlantic and Mediterranean Atherina' species. In European waters, two groups were found. The first clade formed by a well supported species-pair: Atherina presbyter (eastern Atlantic) and Atherina hepsetus (Mediterranean), both living in marine waters; a second clade included Atherina boyeri (brackish and freshwater environments) and two independent lineages of marine punctated and non-punctated fishes, recently proposed as separate species. Sequence divergence values strongly suggest multiple species within the A. boyeri complex.     

Citogenetic characterization of the tropical freshwater fish Parachromis managuensis (Pisces: Cichlidae)

To describe the cytogenetics of the jaguar cichlid fish Parachromis managuensis, we collected eight males and 13 females in Villahermosa, Tabasco, México. The specimens were processed with standard cytogenetic techniques (slightly modified), and high quality fields of chromosomes in mitosis and meiosis were obtained; 14 of these fields were analyzed by meristics and statistics methods. The specimens presented a diploid modal number of 2n = 48 chromosomes, which is similar to the number reported for others Central American cichlids; five pairs were submetacentric-metacentrics (biarmed) and 19 were subtelocentric-telocentric (uni-armed), giving a fundamental number (NF) of 58. The haploid number was confirmed by counting meiotic fields in metaphase I. There was not evidence of heteromorphism: sexual chromosomes were not identifiable.     

Histological study of the development of the embryo and early larva of Oreochromis niloticus (Pisces: Cichlidae)

The developmental stages of Oreochromis niloticus are similar to those described in other mouth-breeding tilapias except that, as in zebrafish, no cavity was found in the blastula. Variation in the rate of development of the embryo and larva of O. niloticus was found within a clutch of eggs as well as between clutches. Hatching glands are described for the first time in tilapias. They are widely distributed within the ectoderm covering the head, body, tail, and surface of the yolk sac near its attachment to the embryo. Timing of larval development is similar to that in other mouthbrooding tilapias, but is slower than that found in substrate-spawning tilapias. A pneumatic duct connects the swimbladder to the digestive tract and swimbladder inflation and initiation of feeding occurs at about the same time. The digestive tract of the larva 8 and 9 days after fertilization is similar to that found in the adult, except that there are no digestive glands. An endocrine pancreatic islet was first seen 76 h after fertilization. A prominent thymus gland is present at 100 h. Hematopoietic tissue develops in the vicinity of the pronephros during early larval development. A spleen develops later, 7 days after fertilization.     

Histopathology in Atherina boyeri (Pisces: Atherinidae) resulting from infection by Telosentis exiguus (Acanthocephala)

The histopathology developing in the sand smelt Atherina boyeri Risso 1810 from Northern Italy as the result of a natural infection by Telosentis exiguus Von Linstow 1901 (Acanthocephala) was studied and described. Microscope examination of sections of intestinal tissues showed that the parasites did not penetrate through all intestinal layers, and that damage was mostly limited to the epithelium.     

Functional responses during the early larval stages of the charal fish Chirostoma riojai (Pisces: Atherinidae) fed rotifers and cladocerans

Survival during early fish larval stages depends largely upon the availability of appropriate prey. Studied were the functional responses from hatching to 6 weeks of age of whitefish (Charal) (Chirostoma riojai) larvae that were offered selected rotifers (Brachionus rotundiformis and B. rubens) and cladocerans (Moina macrocopa and Ceriodaphnia dubia). The experiments were conducted in a 50 ml medium at a salinity of 2 g L^?1. Each treatment used four replicates. Rotifers were introduced at densities of 0.5, 1, 2, 4, 8 and 16 individuals ml^?1 and cladocerans at 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 4.8 and 6.4 individuals ml^?1. Two larvae, previously starved for 2 h, were introduced into each test jar and allowed to feed for 45 min. The difference between the initial and final zooplankton density represented prey consumption. C. riojai larvae showed Type II functional response curves, i.e. they consumed more zooplankton with increasing prey availability; above a certain prey density (8–16 individuals ml^?1 in rotifers and 3.2–6.4 individuals ml^?1 in cladocerans) the consumption rate tended to stabilize in most trials. Results are discussed in relation to aquaculture.     

Development of the embryo, larva and early juvenile of Nile tilapia Oreochromis niloticus (Pisces: Cichlidae). Developmental staging system

We described the developmental stages for the embryonic, larval and early juvenile periods of Nile tilapia Oreochromis niloticus to elucidate sequential events of craniofacial development. Craniofacial development of cichlids, especially differentiation and morphogenesis of the pharyngeal skeleton, progresses until about 30 days postfertilization (dpf). Because there is no comprehensive report describing the sequential processes of craniofacial development up to 30 dpf, we newly defined 32 stages using a numbered staging system. For embryonic development, we defined 18 stages (stages 1-18), which were grouped into seven periods named the zygote, cleavage, blastula, gastrula, segmentation, pharyngula and hatching periods. For larval development, we defined seven stages (stages 19-25), which were grouped into two periods, early larval and late larval. For juvenile development until 30 dpf, we defined seven stages (stages 26-32) in the early juvenile period. This developmental staging system for Nile tilapia O. niloticus will benefit researchers investigating skeletogenesis throughout tilapia ontogeny and will also facilitate comparative evolutionary developmental biology studies of haplochromine cichlids, which comprise the species flocks of Lakes Malawi and Victoria.     

Reproductive behavior of the Atlantic silverside,Menidia menidia (Pisces,Atherinidae)

Synopsis The spawning behavior of the Atlantic silverside,Menidia menidia, was studied at two sites on the North Edisto River estuary in South Carolina. Prespawning schools moved back and forth along the shoreline as the time of high tide approached. Spawning runs took place in the upper intertidal zone at high tide.Spawning fish deposited their eggs on three types of substrates: 1) the lower stems of cordgrass plants,Spartina alterniflora, 2) detrital mats, and 3) exposed cordgrass roots along erosional scraps. Spawning behavior during egg deposition and fertilization was similar for all three substrates. Females released eggs during a rapid fluttering motion of the posterior half of the body. A similar movement accompanied release of sperm by males. Behavior of fish just prior to spawning insured deposition of gametes at locations that provided protection from thermal and drying stress during development. Eggs were deposited at mean intertidal elevations of 1.8 and 1.5 meters above mean low water (MLW) at respective study sites. They were exposed to the atmosphere for approximately ten hours between successive high tides.During spawning runs in which eggs were deposited at the base of cordgrass plants, ambient dissolved oxygen concentrations of the water in the spawning area were sometimes reduced to < 1.0 mg. 1^–1. Spent fish, apparently incurring an oxygen debt while spawning, formed a nonschooling aggregation offshore from the spawning zone.The recurrent use of specific spawning substrates for egg deposition resulted in an uneven distribution of spawning runs along the shoreline at each study site.Contribution No. 409 to the Gulf Breeze Environmental Research Laboratory. Contribution No. 377 to the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

Diet of the tropical fish Gobioides broussonnetii (Pisces: Gobiidae) at Laguna de Unare, Venezuela

Unare Lagoon is one of the most important fishery coastal ecosystems in Venezuela. For the past 10 years, changes in its hydrological regime have affected the physiochemical characteristics of the water with important consequences on its faunal composition and abundance. An example of such variation is the abundant presence ofa fish species, Gobioides broussonnetii, recently registered in this ecosystem. The ecology of this species must be studied to identify new ecological processes occurring in the lagoon. Detritus is the most important component of the G. broussonnetii diet, followed by plant and animal items. The species is a primary detritivorous consumer and this may be associated with its activity pattern (morning): It may be an occasional visitor because it was not captured regularly in the monthly samplings.     

河鲈胚胎及卵黄囊期仔鱼发育

为探究河鲈(Perca fluviatilis)早期生活史和发育生物学,采用体视解剖镜、显微镜仔细观察、测量、描述、绘图的方法,连续观察了6个批次河鲈胚胎及卵黄囊期仔鱼发育状况,进行比较分析。结果显示:(1)在水温8~13℃时,胚胎期约需265h,有效积温2540~2880℃.h;水温11~13℃时,卵黄囊期约需6d,有效积温1750~2120℃.h;(2)辐射状次级卵膜将受精卵连成长带形单层网片状,每个胚胎周围有6个胚胎,排列很有规则。胚胎卵黄囊表面有一个大圆形油球。出膜前期可见眼球色素、胸鳍突起;(3)胚胎出膜的不同步主要是由于出膜前期长短不一和孵化水温较低所致。     

Morphological variation in British Atherinids, and the status of Atherina presbyter Guvier (Pisces: Atherinidae)

A series of morphometric and meristic analyses conducted on specimens of sand smelt, Atherina , from populations around the British Isles, and including classic A. boyeri and A. presbyter forms, has shown that the characteristics variously used in the past to distinguish these two species are invalid. Multivariate analyses showed no significant splitting of the material into two groups which might correlate to these two species; classic A. boyeri and the very large Atlantic coast A. presbyter individuals represent the tails of a continuum of form. From these and published data, it is concluded that the A. boyeri morphology varies under the influence of conditions of temperature and salinity during embryo development, and the isolation of populations maintains comparative morphological distinctions resulting from local selection and random genetic drift.     

Phylogenetic relationships of Atherina hepsetus and Atherina boyeri (Pisces: Atherinidae) populations from Greece, based on mtDNA sequences

The genetic divergence and the phylogenetic relationships of six Atherina boyeri (freshwater and marine origin) and five Atherina hepsetus populations from Greece were investigated using partial sequence analysis of 12s rRNA, 16s rRNA and control region mtDNA segments. Three different well divergent groups were revealed; the first one includes A. boyeri populations living in the sea, the second includes A. boyeri populations living in the lakes and lagoons whereas the third one includes all A. hepsetus populations. Fifty-seven different haplotypes were detected among the populations studied. In all three mtDNA segments examined, sequence analysis revealed the existence of fixed haplotypic differences discriminating A. boyeri populations inhabiting the lagoon and the lakes from both the coastal A. boyeri and the A. hepsetus populations. The genetic divergence values estimated between coastal (marine) A. boyeri populations and those living in the lagoon and the lakes are of the same order of magnitude as those observed among coastal A. boyeri and A. hepsetus populations. The results obtained by different phylogenetic methods were identical. The deep sequence divergence with the fixed different haplotypes observed suggests the occurrence of a cryptic or sibling species within A. boyeri complex.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 151–161.     

Planktivory by larval Odontesthes bonariensis (Atherinidae: Pisces) and its effects on zooplankton community structure

This paper describes the effect of predation by larvae of theatherinid Odontesthes bonariensis upon the zooplankton communityduring a 3-month experiment Three-day-old larvae were stockedin 45 m² concrete tanks at rates of 100 and 200 fish m^–2Gut content analyses showed that the larvae consumed relativelysmall prey all along the experiment Morphological (mouth width)and physiological (gastric inefficiency) constraints seems tohave precluded the capture of the largest prey. The prey community,however, showed all the symptoms generally ascribed to size-selectivepredation upon the largest individuals: decrease in maximumzooplankton size and mean cladoceran size, decrease in cladoceranand copepod biomass, extinction of the largest zooplankton species(Daphnia stmilis), increase in rotifer biomass, etc It is concludedthat size-selective predation is not a necessary condition forthe commonly observed decrease in zooplankton size after theincrease in density of a vertebrate predator. The ecologicalimplications of this result are discussed. Present address: Department of Biology, Lehigh University, WilliamsHall 31, Bethlehem, PA 18015-3189, USA     

On the reproductive biology of the sand smelt Atherina boyeri Risso (Pisces: Atherinidae) and its evolutionary potential

The small, typically estuarine fish Atherina boyeri Risso forms local populations which can differ greatly in their population biology and morphology; this species is viewed as being on the brink of speciation. This analysis of the reproductive strategy shows that A. boyeri can rapidly adapt its life history and morphology to environments ranging from freshwater to polyhaline coastal lagoons and oceanic waters. The optimum strategy is shown to be tied to temperate seasonality: the cold winters act to lengthen the life cycle, and result in cyclic switching of energy between reproduction, somatic growth and fat storage. The adaptability of the fish to a range of environmental characters is viewed as being due to natural selection acting to produce a genotype capable of a flexible phenotypic response. This flexibility is essential for survival in the highly variable inshore/brackish habitat. It is argued that such preadaptive plasticity, coupled with the potential for populations to become isolated, produces ideal conditions for speciation. The importance of the coastal, estuarine and lagoonal environment as a springboard for teleost evolution is discussed.     

Bacterial involvement in a saddleback disease of the reef silverside, At henna harringtonensis Goode (Pisces: Atherinidae) from Bermudan waters

Saddle-shaped skin lesions commonly occurring in both wild and captive Bermudan reef silversides yielded a mixed infection of motile and non-motile Gram-negative cells of Acinetobacter calcoaceticus, Aeromonas hydrophila, Pseudomonas sp., Vibrio parahaemolyticus and a myxobacterial-like strain. Bacteria occurred as almost pure microcolonies and mixed clumps on proximal scale and fin ray surfaces, in intercellular epidermal spaces, on perimysium of fin erector muscle myomeres and on eroded dorsal fin rays and their intact membranes, but neither on healthy areas of the skin nor within muscle cells. Effects were epithelial destruction and liquefactive necrosis of myomeres, and raising and sloughing of Malpighian cells, scales and dermis. Host response was minimal, consisting of infiltration of a few lymphocytes and macrophages. The fish pathogenic dinoflagellate Amyloodinium ocellatum was seen in one fish with a saddle lesion and caused muscle cell lysis, as evidenced by cloudy cell swelling. Antibiotic sensitivity tests showed increased drug resistance with mixed bacterial types compared to that of single pure isolates. This suggests that alternatives to chemotherapy for control of bacterial fish diseases is appropriate, because most are probably caused by mixed infections.