Expressed sequence tags derived from brain tissue of Oreochromis niloticus

Expressed sequence tags (ESTs) were obtained from complementary DNA libraries derived from the brain of the cichlid fish, Oreochromis niloticus. Single-pass sequencing of 183 cDNA clones generated 294 ESTs; 57 of these clones (31%) were identified based on their similarity to sequences in GenBank.     

Rodlet cells in the posterior intestine of embryos and neonates of two poeciliid species

Rodlet cells occurred in the posterior intestine of embryos and neonates of the swordtail Xiphophorus nigrensis , its hybrids with Xiphophorus pygmaeus and in the platyfish Xiphophorus maculatus . This is the first observation of these enigmatic cells in a viviparous teleost prior to birth. This finding lends support to the endogenous tenet regarding the origin of this cell.     

The rate of uptake of sex steroids from water by Tinca tinca is influenced by their affinity for sex steroid binding protein in plasma

Two experiments were carried out in which male and female tench Tinca tinca were placed in individual containers and tritiated steroids then added to the water. Water samples were collected over the next 6 or 7 h and the fish then sacrificed, bled and the gall bladder removed. Radioactivity was counted in all the samples. Over the course of the exposure period in the first experiment (7 h), radioactivity of 11‐ketotestosterone (11‐KT) in the water was depleted by 11%, 17,20β‐dihydroxypregn‐4‐en‐3‐one (17,20ß‐P) and 17,20α‐dihydroxypregn‐4‐en‐3‐one (17,20α‐P) by 28%, testosterone (T) by 56% and androstenedione (AD) by 68%. HPLC analysis of water samples at 3 h indicated that none of the steroids was extensively metabolized during the experiment. Females had a faster rate of uptake of AD than males. In the second experiment (6 h), radioactivity of cortisol in the water was depleted by 5%, 11‐KT by 7%, 17‐hydroxypregnen‐4‐ene (17‐P) by 17%, 17β‐oestradiol (E₂) by 35%, T by 37% and AD by 44%. In both experiments, the amounts of radioactivity that were recovered from the gall bladder and plasma were positively correlated with the rate of disappearance of radioactivity from the water. The ability of the steroids to bind to sex steroid binding protein (SBP) of tench plasma was tested by incubating plasma with radioactive steroids and then separating bound and free with ice cold dextran‐coated charcoal. When plasma at a final dilution of 1 : 60 (v/v) was incubated with 5 nM of each steroid, the percentage of radiolabel bound to SBP was: T 48% AD 44%, E₂ 30%, 17‐P 17%, 11‐KT 13·2%, 17,20α‐P 10·3%, 17,20β‐P 4·5% and cortisol 0%. Saturation analysis established dissociation constants (K_d; mean ± s .e .) of 3·4 ± 0·4, 2·2 ± 0·2, 4·0 ± 0·3. 9·0 ± 2·8 and 51·8 nM and binding capacities (B_max) of 201 ± 29, 201 ± 33, 165 ± 3, 187 ± 15 and 13·4 nM for T, AD, E₂,17‐P and 17,20β‐P respectively. The ability of steroids to displace tritiated T and AD from SBP was in the rank order AD > T > E₂ > 17,20αP = 17,20β‐P = 11‐KT = 17‐P > cortisol. Thus, the ability of tench plasma to bind certain steroids showed a relatively strong correlation with the ability of the fish to take up these steroids from water. Modelling of data for AD and 17,20β‐P helped to show why and how plasma binding had a strong influence on the rate of uptake (and hence release) of the steroids.     

Variation of male reproductive apparatus in relation to fertilization modalities in the catfish families Auchenipteridae and Callichthyidae (Teleostei: Siluriformes)

To investigate the relationship between fertilization modalities and the morphology of male reproductive apparatus, two species of Auchenipteridae, Auchenipterus nuchalis and Tatia intermedia , and six species of Callichthyidae, Callichthys callichthys , Corydoras aeneus , Corydoras bondi , Corydoras ehrhardti , Corydoras potaroensis and Hoplosternum littorale were studied. The species analysed show either internal or external fertilization, the latter including the so called 'sperm drinking' type of mating. An anal fin modified as an intromittent organ, a pair of seminal vesicles, and the release of sperm in the form of discrete bundles (spermatozeugmata) characterize the male reproductive apparatus of the internal fertilizer A. nuchalis . Seminal vesicles are present also in C. aeneus , C. bondi , C. ehrhardti , C. potaroensis and H. littorale , species performing 'sperm drinking' spawning. In contrast, regardless of the family, species showing the more classic type of external fertilization lack specialized accessory organs. Where occurring, the major function of seminal vesicles is the secretion of mucins. The role of these mucosubstances, in relation to spermatozeugmata formation, in internal fertilizers, or the protection of sperm passing through the female gut, in the 'sperm-drinking' species, is discussed. Variation, between families, in the shape of testis and accessory structures, as well as in the type of spermatogenesis was found. Neither the reproductive modalities nor the phylogenetic relationships, however, appear to fully account for these differences.     

Stimulation of dopamine D1 receptor improves learning capacity in cooperating cleaner fish

Accurate contextual decision-making strategies are important in social environments. Specific areas in the brain are tasked to process these complex interactions and generate correct follow-up responses. The dorsolateral and dorsomedial parts of the telencephalon in the teleost fish brain are neural substrates modulated by the neurotransmitter dopamine (DA), and are part of an important neural circuitry that drives animal behaviour from the most basic actions such as learning to search for food, to properly choosing partners and managing decisions based on context. The Indo-Pacific cleaner wrasse Labroides dimidiatus is a highly social teleost fish species with a complex network of interactions with its ‘client’ reef fish. We asked if changes in DA signalling would affect individual learning ability by presenting cleaner fish two ecologically different tasks that simulated a natural situation requiring accurate decision-making. We demonstrate that there is an involvement of the DA system and D₁ receptor pathways on cleaners'' natural abilities to learn both tasks. Our results add significantly to the growing literature on the physiological mechanisms that underlie and facilitate the expression of cooperative abilities.     

A high molecular weight glycoprotein in seminal plasma is a sperm immobilizing factor in the teleost Nile tilapia, Oreochromis niloticus

Sperm that have acquired potential for motility are kept immotile in seminal plasma in the teleost, Nile tilapia. In order to investigate the mechanism of immobilization, several experiments were performed using a previously characterized monoclonal antibody (TAT-30) against a molecular weight (Mr) = 120,000 protein that is secreted by Sertoli cells and epithelial cells of the sperm duct, and is also bound to the head of the spermatozoon. First, we assessed sperm motility in the seminal plasma protein fraction (SPP), and demonstrated that the sperm motility is inhibited by SPP in a concentration-dependent manner. Furthermore, sperm motility was recovered if SPP was pretreated with TAT-30, suggesting that the TAT-30 antigen is one of the components of the sperm immobilizing factor. Calibration by gel filtration followed by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting with TAT-30 demonstrated that the sperm immobilizing factor was more than Mr = 1,000,000 in seminal plasma, suggesting that it is a homopolymer of the Mr = 120,000-TAT-30 positive protein. Additionally, lectin blot analysis showed that the TAT-30 antigen was reactive with Lens culinarin agglutinin (LCA) and Conavalia ensiformis agglutinin (ConA), indicating that it is a glycoprotein. Immunohistochemical studies showed that the TAT-30 antigen was localized specifically on the heads of spermatozoa and on the apical surface, lysosomes and rough endoplasmic reticulum of Sertoli cells.     

Quantitative Assay of Cyclin-Dependent Kinase Activity As a Sensitive Marker of Cell Proliferation in Marine Teleost Larvae

An evolutionarily conserved family of cyclin-dependent kinases (Cdks) regulates cell cycle progression in eukaryotes. Mitosis-promoting factor (MPF) is a transiently activated Cdk required for mitosis. We propose use of partially purified MPF kinase activity as a sensitive marker of cell proliferation in marine teleost larvae and describe a quantitative spin-filter assay of suc1-precipitated MPF activity. MPF extracted from embryos and larvae of red drum, Sciaenops ocellatus, phosphorylated histone H1 protein and a Cdk-specific peptide substrate. Kinetic analyses demonstrated that apparent K _m values of red drum MPF for adenosine triphosphate and the peptide substrate were 98.3 and 18.2 μM, respectively. A simple growth experiment showed that MPF activity was significantly greater in rapidly growing red drum larvae than in intermittently fed cohorts growing more slowly. Received July 23, 1998; accepted January 14, 1999     

Characterization of morphology and physiological actions of scale osteoclasts in the rainbow trout

The morphology of scale osteoclasts in rainbow trout Oncorhynchus mykiss was characterized by light and scanning electron microscopy, and the effects of oestradiol-17β-treatment and sexual maturation on scale osteoclast morphology were investigated. The cells associated with resorption cavities could be distinguished morphologically as two types: symmetrical, compact cells lacking or having only a few cell processes, termed type 1 cells, and asymmetrical cells covered with folds and having several cell processes, termed type 2 cells. In adult sexually maturing fish, where scale resorption was high, type 1 cells were predominant. In juveniles and spawned adults where scale resorption was assumed to be relatively low, mostly type 2 cells were present. Oestradiol 17-β-treatment of juvenile rainbow trout increased the osteoclast activity, but did not affect the osteoclast morphology. Using light microscopy, the majority of the cells observed in, and closely associated with, the resorption cavities were mononucleated in both maturing and spawned fish. Occasionally, bi- and multinucleated osteoclasts were observed in the maturing, but not in the spawned fish. Light microscopic enzyme-histochemistry showed that the majority of the mononucleated cells, as well as the bi- and multinucleated ones, were tartrate resistant acid phosphatase positive in both groups of fish, thus implying that both type 1 and type 2 cells were osteoclasts. It is thus apparent that scale resorption in rainbow trout is carried out by two morphologically distinct osteoclast populations, representing different stages of osteoclast activity and/or different stages of osteoclast differentiation.     

Diet and reproduction in the Australian butterfly ray Gymnura australis from northern and north‐eastern Australia

The diet of Gymnura australis was dominated by teleosts (99·8% index of relative importance). A wide‐ranging species, females matured at 446 mm disc width (W_D), had a single functional ovary and two functional uteri. Males matured at 377 mm W_D and had a single functional testis.