Residual biparental oral-brooding in the blackchin fish, Sarotherodon melanotheron Rüppell

Sarotherodon melanotheron generally shows a paternal brooding habit, but females of one of the strains in Ghana also exhibit the potential for oral-brooding.     

Effect of temperature on growth of juvenile Oreochromis mossambicus and Sarotherodon melanotheron

Synopsis Survival and competitive ability of juvenile fish is often dependent on their growth rate. Temperature is the physical component of their environment which most affects growth rate. To determine the effect of temperature on the growth rate of two exotic warm water species we measured growth of Oreochromis mossambicus and Sarotherodon melanotheron at 25, 30 and 35°C. There was a significant interaction of species and temperature on growth. The growth rate of O. mossambicus was faster than that of S. melanotheron at 25 and 30°C but slower at 35°C. Weight gain of S. melanotheron was significantly greater at 30°C than at 25°C. Weight gain of O. mossambicus at 25 and 30°C was significantly greater than at 35°C. Temperature had no effect on the weight-length relationship of either species.Scientific Series No. 1546-AEL from UM-CEES, Appalachian Environmental Laboratory     

Impact of environmental DDT concentrations on gill adaptation to increased salinity in the tilapia Sarotherodon melanotheron

Estuaries of tropical developing countries suffering from severe droughts induced by climate change are habitats to fish, which face drastic salinity variations and the contact with pollutants. The Western Africa tilapia Sarotherodon melanotheron is highly resistant to hypersalinity, but the effect of human-released xenobiotics on its adaptation is barely known. Controlled experiments were conducted to observe S. melanotheron gill adaptation to abrupt salinity variations in the presence of waterborne DDT, at concentrations detected in their natural habitat. The gills appeared as an important site of DDT conversion to DDD and/or depuration. A 12-days DDT exposure resulted in decreased gill epithelium thickness at all salinities (from fresh- to hypersaline-water), and the structure of gills from freshwater fish was particularly altered, relative to controls. No unbalance in tilapia blood osmolality was observed following DDT exposure, which however caused a decrease in branchial Na(+)-K(+)-ATPase (NKA) activity. Gill cellular NKA expression was reduced in salt-water, together with the expression of the CFTR chloride channel in hypersaline water. Although S. melanotheron seems very resistant (especially in seawater) to short-term waterborne DDT contamination, the resulting alterations of the gill tissue, cells and enzymes might affect longer term respiration, toxicant depuration and/or osmoregulation in highly fluctuating salinities.     

The effects of lowered temperature on spontaneous eye movements in a teleost fish

A new opto-electronic method has been used to measure spontaneous eye movements in a lightly restrained unanaesthetized marine teleost fish (Parore). The normal scanning pattern of eye movement is similar to that previously described in goldfish. The effects of cooling on eye movements were investigated by 2 degrees C step changes down from ambient temperature (13-14 degrees C). Lowered temperature altered the scanning pattern, decreased saccade velocity, increased mean saccade amplitude and impaired the ability of the fish to hold the eye stationary between saccades. All eye movements stopped at temperatures around 6 degrees C, but could be restored by subsequent warming.     

Kin cohesiveness and possible inbreeding in the mouthbrooding tilapia Sarotherodon melanotheron (Pisces Cichlidae)

Four microsatellite markers were used to study genetic variation among individuals of the mouthbrooding tilapia Sarotherodon melanotheron (Rüppel 1852) caught in separate but adjacent shoals. A comparison was also made with fish from six other localities. Populations originating from riverine environments appear to be panmictic, while samples from open waters such as lagoons showed highly significant heterozygote deficiencies. For instance, at the 33-allele locus SMEL4, 32 homozygous individuals were observed among the 82 individuals from the same lagoon location instead of only five homozygotes expected if random mating occurred. A further assessment of the genetic similarity of individuals within each shoal, validated by robust permutation techniques requiring no precise knowledge of gene frequencies, showed that related individuals tend to aggregate, and suggested that mating occurs preferentially within small groups of kin. Cichlids are often presented as a group of fish where microallopatric speciation takes place. The possible link between kin aggregation, inbreeding and shoaling behaviour we propose here may have important consequences for our understanding of the mechanisms involved in this fast speciation process.     

The effects of ciguatoxin on the nerves of the teleost fish, Sillago ciliata.

The absolute refractory period, relative refractory period, and the duration and magnitude of the supernormal period were measured after incubation of fish nerves with ciguatoxin and other channel modifying compounds, tetrodotoxin, veratridine, verapamil, and lignocaine. In vitro electrophysiological studies were carried out on the lateral line nerve of the whiting, Sillago ciliata Cuvier. Electrophysiological changes in fish nerves after exposure to ciguatoxin (0.3 MU.ml-1) and veratridine (1 x 10(-5) M) are similar to changes that occur in mammalian nerves and include an increase in the absolute refractory period, the relative refractory period, and the magnitude and duration of supernormality. The effects of ciguatoxin (0.3 MU.ml-1) in fish nerves were antagonised by tetrodotoxin (5 x 10(-10) M), verapamil (5 x 10(-7) M), and lignocaine (1 x 10(-5) g/ml-1). The nerves of Sillago ciliata used in this study responded to ciguatoxin and its antagonists in a similar manner to mammalian nerves, suggesting that these teleost nerves have no specific electrophysiological mechanism to cope with this toxin.     

Changes in developmental profiles of brain gangliosides during ontogeny of a teleost fish (Sarotherodon mossambicus,Cichlidae)

Summary Ontogenetic changes of brain ganglioside concentration and composition have been followed in the teleost fishSarotherodon mossambicus Cichlidae) from the 1st day post hatching to the adult stage, in order to correlate these with findings in higher vertebrates. During the developmental period from hatching to the transition to free swimming, which comes along with maximum rate of synaptogenesis, a sharp rise in the brain ganglioside content occurs, which is mainly due to the trisialoganglioside GT1b. In the following phase of myelination (characterized in birds and mammals by an increase in GM1, GM1 and GM4) accretion of the novel and so far unidetified fraction (GM2) occurs, which is highly enriched in the brain stem. The results obtained are discussed with respect to gangliosides as useful biochemical markers for brain development and maturation in all vertebrates.     

Osmoregulatory strategies in natural populations of the black-chinned tilapia Sarotherodon melanotheron exposed to extreme salinities in West African estuaries

The effect of salinity was studied in natural populations of the black-chinned tilapia (Sarotherodon melanotheron) from West Africa. This euryhaline species colonizes nearly all coastal environments from bays to lagoons characterized by salinities ranging from fresh water to hypersaline water over 100 ‰. Individuals were sampled during the dry season at several locations characterized by different levels of salinity (3-102 ‰). Their osmotic status and their gills were analyzed. The branchial mitochondria-rich cells (MRC), localized at the basis of the filaments and along the lamellae in fish taken from the saline stations, showed a wide plasticity with significant differences in their number and size. The most striking results were a significant larger area (≈3x) and a higher number (≈55x) of MRC at high salinity (102 ‰) compared to low salinity (3 ‰). The major ion transporters and channels were localized by immunocytochemistry and different expression patterns have been recorded between stations. Despite an increased Na?/K?-ATPase (NKA) α-subunit expression and NKA activity, pointing to an increased monovalent ion excretion, a severe osmotic imbalance was recorded in animals living in hypersaline environments.     

The effect of water acidification on prolactin cells and pars intermedia PAS-positive cells in the teleost fish Oreochromis (formerly Sarotherodon) mossambicus and Carassius auratus

Summary Although exposure to acid water (pH 3.5) induces severe and prolonged reduction in plasma osmolarity and total plasma calcium concentration in tilapia (Oreochromis mossambicus) and goldfish (Carassius auratus), the responses of the hypophyseal cells are clearly different. In tilapia, the size of the rostral pars distalis of the pituitary gland is enlarged as a result of the increase in size and number of prolactin cells. The pars intermedia PAS-positive (PIPAS) cells are not noticeably changed. Conversely, in goldfish, prolactin cells are unaffected, whereas the number of enlarged PIPAS cells increases markedly. Stimulation of prolactin secretion may be responsible for the partial restoration of plasma osmolarity and calcium levels observed in tilapia after two weeks exposure to acid water. Prolactin cells apparently play a role in the adaptation to acid stress by counteracting osmoregulatory disturbances. Goldfish show no restoration of plasma osmolarity during the course of the experiment. Plasma calcium levels tend to increase. Although prolactin may have an osmoregulatory function in goldfish under steady state conditions, goldfish prolactin cells do not seem to participate in the physiological adaptation to environmental changes that disturb water and ion homeostasis. The function of PIPAS cells in tilapia remains unclear and is apparently unconnected with ion regulation. The observations on these cells in goldfish are consistent with the hypercalcemic activity suggested for them.     

The hapten-carrier effect in teleost fish.

The sea robin (Prionotus evolans), a representative teleost fish, was found to undergo the hapten-carrier effect, suggestive of T-B cell cooperativity, in vivo with dinitrophenyl as the hapten and bovine gamma-globulin or bovine serum albumin as carriers. In contrast to mammalian systems, the secondary anti-hapten response in the sea robin was found to involve exclusively high molecular weight antibody.     

Behavioral aspects of cold tolerance in blackchin tilapia,Sarotherodon melanotheron,at different salinities

Synopsis Cold tolerance and behavioral responses of blackchin tilapia, Sarotherodon melanotheron, to rapidly decreasing temperatures were investigated at salinities of 5, 15, and 35 parts per thousand (ppt). Cold tolerance did not significantly differ with salinity or social rank. Mean temperatures were 10.7° C for beginning loss of equilibrium, 9.6° C for complete loss of equilibrium, and 6.9° C for death at all salinities. Behavioral activity declined with decreasing temperature and ceased between 10–12° C. Certain behavioral actions were significantly more frequent at 15 or 35 ppt salinity than at 5 ppt. The northward range expansion by introduced populations of the blackchin tilapia in the United States probably will be limited by its lower lethal temperature limits, but may also be affected by temperatures at which social behavior becomes disrupted.     

Opposite effects of nonapeptide antagonists on paternal behavior in the teleost fish Amphiprion ocellaris

The nonapeptides isotocin (IT) and arginine vasotocin (AVT), along with their mammalian homologs oxytocin and arginine vasopressin, are well known regulators of social behaviors across vertebrate taxa. However, little is known about their involvement in paternal care. Here, we measured the effect of an IT and an AVT V1a receptor antagonist on paternal behaviors in the primarily paternal teleost Amphiprion ocellaris. We also measured the effect of the IT receptor antagonist on aggression in dyadic contests between two non-reproductive fish to assess specificity of the effect on paternal behaviors. Individual differences in levels of paternal behaviors (nips, fanning the eggs, and proportion of the time in the nest) were consistent across spawning cycles when no treatments were administered. The IT receptor antagonist severely reduced paternal behaviors but had no effect on aggression, whereas the AVT V1a receptor antagonist increased paternal behaviors. These results support the idea that IT signaling is crucial for the expression of paternal behavior in A. ocellaris. Based on a previous study showing that the AVT V1a antagonist decreases aggression in dyadic contests, we hypothesize that the antagonist enhances paternal behavior indirectly by reducing vigilance and aggression, thereby alleviating effort directed towards other competing behaviors and allowing for the increased expression of paternal behaviors.     

Reproduction of Blackchin Tilapia, Sarotherodon melanotheron, Within an Impounded Mangrove Ecosystem in East-central Florida

I investigated the reproductive biology of introduced blackchin tilapia, Sarotherodon melanotheron, over a twelve month period within a seasonally impounded mangrove ecosystem in east-central Florida, and compared the data to published accounts from native African habitats. Eggs and free embryos were collected from the buccal cavity of adult males from April to October indicating a protracted spawning season, however gonadosomatic indices suggested that most spawning occurred in April and May. The timing of reproduction was adjusted to occur immediately before temperatures reached optimal levels for juvenile growth and when increasing rainfall produced abundant food and shelter for the young. Temperatures below 24°C inhibited reproduction from November to March. The overall sex ratio was essentially 1:1. The minimum and maximum size at maturity were much larger in this study than those reported from Africa; the smallest mature male was 128mm standard length and 0.47 of the maximum size, while the smallest mature female was 145mm standard length and 0.54 the maximum size. However, because of the difficulty in aging this species and a lack of published information, it could not be determined whether the population in this study possessed a relatively early or delayed maturation compared to African populations.     

The role of aquaporin 3 in teleost fish

The aquaporin isoform, AQP3 has now been identified in a number of different teleost fish species, with additional DNA sequence information on AQP3 genes in further fish species available in genome databases. In zebrafish (Danio rerio), the AQP3 gene is present as two duplicate isoforms resulting from a teleostean fish genome-wide duplication. A further splicoform/isoform has also been identified in rainbow trout (Oncorhynchus mykiss). The identification of these AQP3 isoforms in other fish species is consequently explored. The role of AQP3 in physiological/osmoregulatory processes, in various teleost organs is then described. In teleost gill, AQP3 is expressed in 'chloride' cells, and in some species, in other epithelial cell types, where it may have a number of different functions including the prevention of dehydration. In eel esophagus, immunohistochemistry shows that AQP3 is expressed in surface epithelial cells in the anterior esophagus, but in mucus cells within the epithelium of the posterior esophagus. In eel intestine, AQP3 is found in macrophage-like cells and probably plays no part in osmoregulatory processes. In the rectum, as in the posterior esophagus AQP3 is expressed in mucus cells. In eel kidney, AQP3 is expressed in a subset of renal tubules, and localizes to the apical pole of tubule cells. There is no apparent change in the location or protein abundance of renal AQP3 following the acclimation of eels from freshwater to seawater.     

Enameloid in the teleost fish Lophius

Summary The ultrastructural and chemical differences between mature enameloid and dentine in the teleost fish Lophius were demonstrated using transmission (TEM) and scanning (SEM) electron microscopy, X-ray diffraction analysis, electron diffraction analysis and electron microprobe analysis. An enameloid cap (about 50 m thick) and a thin layer (1 m thick) of collar enameloid were revealed in the scanning (SEM) and transmission (TEM) electron microscopes. Collar enameloid, structurally different from dentine both in SEM and TEM, proved to be less mineralized than the cap as revealed by electron microprobe analysis. The enameloid cap was seen to differ from dentine by (i) its electron density in TEM; (ii) the structural arrangement perpendicular to the underlying dentine, observed in SEM and TEM and corroborated by electron diffraction data, which showed a preferred orientation of enameloid crystallites; (iii) its higher F content decreasing gradually from the apex of the tooth to the junction with dentine and falling suddenly below this junction; and (iv) its lower Mg content. Establishment of a classification of enameloids is proposed, similar to that for dentines, in which selachian enameloid would be a reference standard.

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Résumé La microscopie électronique à transmission, la microscopie électronique à balayage, la diffraction X, la diffraction électronique et l'analyse par microsonde ont prouvé l'existence d'un émailoïde, ultrastructuralement et chimiquement différent de la dentine, chez la baudroie. La microscopie électronique à balayage et la microscopie électronique à transmission ont mis en évidence un chapeau d'émailoïde, d'environ 50 m d'épaisseur, et une couche fine (1 m) d'émailoïde du collet. L'émailoïde du collet, dont l'ultrastructure différente de celle de la dentine a été mise en évidence en microscopie électronique à transmission et en microscopie électronique à balayage, apparaît, après analyse par microsonde, moins minéralisé que le chapeau. Le chapeau d'émailoïde diffère de la dentine par (i) sa densité aux électrons en microscopie électronique à transmission; (ii) sa structure perpendiculaire à celle de la dentine sous-jacente, visible en microscopie électronique à transmission et en microscopie électronique à balayage et confirmée par la diffraction électronique, qui montre une orientation préférentielle des cristaux; (iii) son contenu en fluor plus élevé, qui diminue progressivement de l'apex à la jonction avec la dentine et chute brutalement au-dessous de cette jonction; (iv) sa teneur plus basse en magnésium. Les auteurs proposent que soit établie une classification des émailoïdes analogue à celle des dentines et dans laquelle l'émailoïde de Sélaciens constituerait un standard de référence.

     

Effects of salinity on strontium:calcium ratios in the otoliths of the West African black-chinned tilapia Sarotherodon melanotheron in a hypersaline estuary

The biology and the behaviour of fish populations in hypersaline environments are poorly known. The habitat occupation strategy of the tilapia Sarotherodon melanotheron has been studied along a salinity gradient in the Saloum hypersaline estuary in Senegal (salinity between 32 and 100). The individual migratory behaviour has been analysed from otolith strontium-to-calcium concentration ratios from fish sampled in five locations during the 2003 wet season and the 2004 dry season. In the upper part of the estuary (salinities > 50), the Sr:Ca ratio in the otolith showed high variations, from 2.51 to 33.30 × 10⁻³. These maximum observed values have never been reported in the literature. The individual mean of Sr:Ca ratios increased according to the salinity gradient in the estuary, with significantly higher values in the upper part (Sr:Ca mean = 16 × 10⁻³) than in the lower part (salinity < 50, Sr:Ca mean = 12 × 10⁻³). No significant difference in the Sr:Ca mean was observed between locations with comparable salinities. Sr concentration in the water at the different locations was positively correlated with ambient salinity. The mean of Sr:Ca in the otoliths was then in relationship with the level of Sr in the water. Thus, the Sr:Ca ratios in the otolith of S. melanotheron allowed to discriminate the populations of this species and to hypothesize that they did not undertake large scale movements within the estuary.     

Catecholaminotropic effects of catecholamines in a teleost fish,Anguilla rostrata

Summary Injections of physiological and supraphysiological doses of epinephrine (E) into cardiaccannulated eels cause a dose-related increase of plasma dopamine (DA) and norepineprine (NE) within 3 min. Likewise, both exogenous DA and NE increase the plasma titers of the respective other two catecholamines (CAs). The baseline titers of NE and E are closely correlated. Lack of a correlation of the baseline titers of NE and E with that of DA appears to be due to a faster disappearance rate of DA from the circulation. E is strongly hyperglycemic, and the weaker glycemic action of NE may be mediated via E release. The effects of E seem to depend on a spurt-like increase rather than its titer per se. The ability of the eel to cope with very fast, excessive increases of plasma CAs raises the question of the underlying mechanisms.Abbreviations CA(s) catecholamine(s) - DA dopamine - NE norepinephrine - E epinephrine