Effects of pinealectomy on pituitary gonadotrophs, pituitary gonadotropin potency and hypothalamic gonadotropin releasing activity in Notemigonus crysoleucas

The effects of pinealectomy on pituitary gonadotrophs, pituitary gonadotropin potency and hypothalamic gonadotropin releasing activity were examined in the cyprinid teleost, Notemigonus crysoleucas, exposed to various photoperiod-temperature regimes. In fish exposed to a long photoperiod-warm temperature regime, pinealectomy resulted in a decrease in gonadal activity, in hypothalamic gonadotropin releasing activity and an increase in pituitary gonadotropin potency. Fewer gonadotrophs were present in the pituitary of sham operated fish than in the pituitary of pinealectomized fish. Ovarian development was more rapid in sham operated than in pinealectomized fish exposed to a long photoperiod–low temperature regime. Pituitary gonadotropin activity was also greater in shams than in pinealectomized fish. A short photoperiod-warm temperature regime retarded ovarian development in N. crysoleucas. Pinealectomy reversed this trend. Gonadotrophs made up a greater area of the pituitary in pinealectomized fish than in shams under these conditions. Gonadotropin potency of the pituitary and hypothalamic gonadotropin releasing activity were also greater in pinealectomized fish than in shams. The area of the pituitary occupied by gonadotrophs was greater in pinealectomized than in sham operated animals maintained on a short photoperiod-low temperature regime. Pituitary gonadotropin activity was also greater in pinealectomized fish as compared to shams. Pituitary gonadotropin potency varies diurnally in animals maintained on both short and long photoperiods; the rhythm of variation differs depending on photoperiod. Pinealectomy alters the diurnal rhythm of pituitary gonadotropin potency in animals exposed to both long and short photoperiods. It is concluded that pinealectomy has a pronounced effect on reproductive activity in N. crysoleucas. The effects of pinealectomy on reproduction vary with photoperiod, but are mediated via the hypothalamus and pituitary. In fish exposed to long daylengths the pineal favours reproductive activity, but the epiphysis retards reproductive processes in animals maintained on short photoperiods.     

Diurnal variations in pituitary gonadotropin content and in gonadal response to exogenous gonadotropin and prolactin in Notemigonus crysoleucas

Diurnal variations in pituitary gonadotropin content were determined in the golden shiner, Notemigonus crysoleucas. In fish maintained on a 15-5L/8-5D–15°C regime, a pronounced circadian variation in pituitary gonadotropin potency was observed, the gonadotropin content being minimal early and maximal late during the light phase. Little temporal variation was seen in fish exposed to a 9L/15D–15°C regime. The effects of gonadotropin and prolactin treatment on gonadal activity in N. crysoleucas were also investigated. Salmon gonadotropin was effective in stimulating an increased rate of gonadal development when given early during the light phase in fish maintained on a 15.5L/8-5D–15°C regime; injections of gonadotropin given late in the light phase failed to accelerate gonadal growth. Regardless of time of injection, ovine luteinizing hormone accelerated gonadal growth in fish maintained on a 9L/15D–15°C regime. Ovine prolactin retarded gonadal development in fish exposed to a 15.5L/8-5D–24°C regime, independent of injection time. In fish maintained on a 15.5L/8-5D–15°C regime, injections of prolactin given early, but not late, during the light phase repressed gonadal maturation. These data show that under certain photoperiod-temperature conditions there is a temporal aspect to responsiveness to exogenous hormone treatment.     

Role of LPXRFamide peptide in the neuroendocrine regulation of reproduction in fish

The decapeptide gonadotropin-releasing hormone (GnRH) is the primary factor responsible for the hypothalamic control of gonadotropin (GTH) secretion. This review focuses on a family of neuropeptides, LPXRFamide (LPXRFa) peptides, which have been implicated in the regulation of GTH secretion. LPXRFa acts on the pituitary via a G protein-coupled receptor, LPXRFa-R, to enhance gonadal development and maintenance by increasing gonadotropin release and synthesis. Because LPXRFa exists and functions in several fish species, LPXRFa is considered to be a key neurohormone in fish reproduction control. The precursors to LPXRFamide peptides encoded plural LPXRFamide peptides and were highly divergent in vertebrates, particularly in lower vertebrates. Tissue distribution analyses indicated that LPXRFamide peptides were highly concentrated in the hypothalamus and other brainstem regions. In view of the localization and expression of LPXRFamide peptides in the hypothalamo-hypophysial system, LPXRFamide peptide in fish increase GTH release in vitro and in vivo. This review summarizes the advances made in our understanding of the biosynthesis, mode of action and functional significance of LPXRFa, a newly discovered key neurohormone.     

Response to De Silva et al. (2007): Endemic freshwater finfish of Asia: distribution and conservation status

De Silva et al . (2007) present an overview of the distribution and conservation status of the endemic freshwater fish of Asia. Within that review they use data from the IUCN Red List of Threatened Species™ (2006) to conduct an analysis of the conservation status of those endemic fish species. Their analysis is incorrect and provides a very misleading impression of the level of threat to Asian freshwater fish and to freshwater fish at the global scale. The errors stem from a misinterpretation of the data presented on the IUCN Red List. The sources of errors are discussed below and the opportunity is taken to clarify what the information on the IUCN Red List represents.     

Proteinases of hydrobionts--potential objects of fish feeding

The review analyzes data on activities and characteristics of proteinases of digestive system and of cathepsins of various tissues in potential preys of fish differing by the character of feeding. There are presented data on multiple forms and molecular mass of proteinases, species-related differences, dependence of proteinase activities on the life cycle stages, type of nutrition, and biochemical food composition as well as on temperature and pH optima. Role of cathepsin in evolution of enzymatic systems providing degradation of food protein components in fish is discussed.     

Proteinases of potential objects of fish nutrition

The review analyzes data on activities and characteristics of proteinases of digestive system and of cathepsins of various tissues in potential preys of fish differing by the character of nutrition. There are presented data on multiple forms and molecular mass of proteinases, species-related differences, dependence of proteinase activities on the life cycle stages, type of nutrition, and biochemical food composition as well as on temperature and pH optima. Role of cathepsin in evolution of enzymatic systems providing degradation of food protein components in fish is discussed.     

Parasitofauna of freshwater fishes in the Serbian open waters: a checklist of parasites of freshwater fishes in Serbian open waters

As a result of freshwater fish parasitofauna investigations, throughout the past 75 years, the number of parasitic species is presented. This paper reviews the history, current state, and tendencies of the fish parasitofauna studies in Serbian open waters. Up to now, in total 170 parasitic species have been reported. Systematic parasitofauna investigations have been carried out on 54 freshwater fish species in waters of the Danube River Basin in Serbia, also in hill-mountanious watercourses, lakes and salmonid fishpond of Sjenicko-Pesterska plateau (south-west region of Serbia), Homolje area (east Serbia), and in Vlasina lake (south-east Serbia). This data review pointed that it is necessary to continue the investigation on fish parasites in Serbia. The data on freshwater fish parasites are important for evaluation of general influence on the community structure.     

Pike eel (Muraenesox cinereus) gonadotropin. Amino acid sequences of both alpha and beta subunits

The amino acid sequences of pike eel gonadotropin alpha and beta subunits have been determined by standard sequencing analytical methods. The alpha subunit is composed of 93 amino acid residues while the beta subunit comprises 113 amino acid residues. All the invariant half-cystine residues are in the same positions as those found in other gonadotropins. It is noteworthy that the first, putative glycosylation site (Asn56) found in the alpha subunit of other gonadotropins was replaced by Asp56 in the alpha subunit of pike eel gonadotropin. Similarity analyses indicate that both subunits are structurally more similar to other known fish gonadotropin subunits than to those of the mammalian gonadotropins.     

The role of amino acid neurotransmitters in the regulation of pituitary gonadotropin release in fish.

Both glutamate and gamma-aminobutyric acid (GABA) are involved in pituitary hormone release in fish. Glutamate serves 2 purposes, both as a neurotransmitter and as a precursor for GABA synthesis. Glutamate can be catabolized to GABA by the actions of 2 distinct but related enzymes, glutamate decarboxylase 65 (GAD65) and GAD67. They derive from 2 different genes that likely arose from an early gene duplication prior to the emergence of teleosts more than 400 million years ago. There is good evidence for the involvement of GABA in luteinizing hormone (LH) release in fish. The mechanism of GABA action to stimulate LH release appears to be a combination of effects on GnRH release, potentiation of gonadotropin hormone-releasing hormone (GnRH) action, and in some cases directly at the LH cell. These actions appear to be dependent on such factors as sex or sex steroid levels, and there may also be species differences. Nevertheless, the stimulatory effects of GABA on LH are present in at least 4 fish species. In contrast, convincing data for the inhibitory effects of GABA on LH release have only been observed in 1 fish species. The sites and mechanisms of action of amino acid neurotransmitters on LH release have yet to be fully characterized. Both 130N-methyl-D-aspartic acid (NMDA) and S-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamate receptors are likely to have important roles. We suggest that it is a receptor similar to the GABA(A) type which mediates the effects of GABA on LH release in fish, at least partially acting on the GnRH neuron, but likely directly acting at the gonadotroph as well. GABA may also be involved in regulating the release of other pituitary hormones in fish, namely follicle stimulating hormone (FSH = GTH-I), prolactin, and growth hormone. Based on the findings described in this review, a working model for the involvement of glutamate and GABA in the regulation of LH release in teleost fish is proposed.     

Effects of in vivo crude human chorionic gonadotropin on ovulation and spawning of the African catfish, Clarias gariepinus Burchell–1822

The effects of increasing dosages of crude human chorionic gonadotropin (cHCG) on ovulation and spawning of Clarias gariepinus Burchell were examined. Four and 5 mg cHCG/100g body weight of fish gave the best response. The activation of the interrenals and stimulation of the ovary are discussed as a possible route of in vivo human chorionic gonadotropin administration on ovulation and spawning in catfish.     

A teleost (Tilapia mossambica) gonadotropin that resembles luteinizing hormone.

A purified gonadotropin preparation was obtained from pituitaries of a teleost fish ($\text{Tilapia}$$\text{mossambica}$). This gonadotropin was found to resemble LH in that it behaved identically to mammalian and non-mammalian LHs in several chromatographic systems, and stimulated testerone production in isolated rat Leydig cells. In this assay, specific for LH, the $\text{Tilapia}$ gonadotropin was less potent than mammalian LHs but significantly more active than avian, reptilian or amphibian LHs. The $\text{Tilapia}$ gonadotropin was found to be a glycoprotein; preliminary amino acid composition data show resemblances to both mammalian and non-mammalian LHs.     

Selective depletion of dopamine in the goldfish pituitary caused by domperidone.

The effects of the dopamine type-2 receptor (D-2) antagonist domperidone on pituitary and brain amine concentrations and serum gonadotropin levels in the goldfish were investigated. Domperidone caused a long-lasting, dose-dependent depletion of dopamine in the goldfish pituitary. Pituitary concentrations of 5-hydroxytryptamine (5HT) were unaffected by domperidone treatment. Concentrations of noradenaline, dopamine, and 5HT in the hypothalamus and telencephalon were also unaffected by domperidone treatment. In contrast to the goldfish, dopamine levels in both mouse pituitary and hypothalamus were unaffected by domperidone treatment. The depletion of dopamine was observed in both sexually regressed and recrudescent, male and female fish, but elevation of serum gonadotropin levels in response to domperidone treatment occurred only in sexually recrudescent fish. Treatment of sexually recrudescent fish with the D-2 antagonists pimozide, (-)-sulpiride and eticlopride and the dopamine type-1 (D-1) antagonists SKF 83566 and SCH 23390 failed to elicit a depletion of pituitary dopamine or elevation of serum gonadotropin. Treatment of sexually recrudescent fish with domperidone, alpha-methyl-p-tyrosine or carbidopa elicited comparable depletions of pituitary dopamine and elevations of serum gonadotropin. The results suggest that in addition to D-2 receptor antagonist activity, domperidone has some other neuropharmacological action on dopaminergic neurones in the goldfish pituitary.     

A checklist of parasites of non-native populations of the fish rotan Perccottus glenii (Odontobutidae): Communication II

The fish rotan, Perccottus glenii Dybowski, 1877 (Odontobutidae) is one of the most successful fish invaders during 20th and beginning of 21st century in European and Asian fresh waters. The diversity of its parasites within its invaded range was first reviewed by Sokolov, Reshetnikov, et al. (2014). The current paper analyzes new data from 2013 to 2019 on protistan and metazoan parasites of the non-native populations of this fish. We used information from peer-reviewed journals, difficult to access grey literature and our own recently obtained original data. 45 literature sources were included in the analysis. The newly-available data originate from 95 water bodies of 13 river basins, isolated lakes in West Siberia, and Gulf of Finland, spanning a total of eight countries. A total of 132 recently detected parasite species/taxa are listed in this paper. Each species is presented with its location in/on the host, geographical localities, countries, and according literature sources. When available, number of examined fish as well as prevalence and range of intensity of infection are cited from the original source. This review enlarges contemporary knowledge on parasites of non-native populations of the studied fish species up to 167 species/taxa. We highlight perspectives for further parasitological investigations of this invasive fish.     

Reproductive Endocrinology of Fishes

While evidence is currently lacking for the agnatha and elasmobranchs,the release of pituitary gonadotropin by the teleost pituitaryappears to be under stimulatory control by the hypothalamus. Gonadotropin has to date only been purified from teleost pituitaryglands. Bioassay and biochemical data suggest that the teleostpituitary gland elaborates only one gonadotropin; however, thereis some conflicting histological data on this point. Salmongonadotropin has a molecular weight of approximately 29,000at neutral pH and approximately 13,000 at low pH or after treatmentwith 8M urea or 1M propionic acid. Radioimmunossays have recently been developed for carp and salmongonadotropin. Immunological techniques have also been used toidentify pituitary gonadotrops. Pharmacological treatment of fish with methallibure has permittedinhibition of gonadal development while treatment with clomiphenecitrate has stimulated ovulation. The role of corticosteroidsand other steroid hormones in ovulation is still not fully elucidated.It is possible that the control of ovulation may differ betweenspecies. Experiments are described which aim to enhance natural stocksof pink salmon by endocrine manipulation of sexual developmentin the male.     

Recent advances in the pharmacologic regulation of fertility in men.

An updated review of research into contraceptives for men is presented. New concepts of the pharmacologic effects of chemical agents on germinal stem cells and spermatogenic arrest, and the effect of new compounds that act at the post-testicular level but do not affect androgen production are discussed. The latest results of studies on steroidal compounds that inhibit pituitary secretion of gonadotropin and hence result in suppression of spermatogenesis and testosterone secretion are presented. The newer contraceptive pills for men are also evaluated. The major drawback to the development of chemical contraceptives for men is the fear of genetic damage and impotence. New and continued research into this type of contraception is urgently needed.     

Modelling spatial dynamics of fish

Our ability to model spatial distributions of fish populations is reviewed by describing the available modelling tools. Ultimate models of the individual's motivation for behavioural decisions are derived from evolutionary ecology. Mechanistic models for how fish sense and may respond to their surroundings are presented for vision, olfaction, hearing, the lateral line and other sensory organs. Models for learning and memory are presented, based both upon evolutionary optimization premises and upon neurological information processing and decision making. Functional tools for modelling behaviour and life histories can be categorized as belonging to an optimization or an adaptation approach. Among optimization tools, optimal foraging theory, life history theory, ideal free distribution, game theory and stochastic dynamic programming are presented. Among adaptation tools, genetic algorithms and the combination with artificial neural networks are described. The review advocates the combination of evolutionary and neurological approaches to modelling spatial dynamics of fish.     

Familial hypothalamic hypogonadotropic hypogonadism

Clinical findings and endocrine studies are reported concerning six subjects (from two pedigrees) suffering from isolated hypogonadotropic hypogonadism. Their complete lack of any gonadotropin response to clomiphene stimulation, together with positive responses of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to LH-releasing-hormone stimulation (LH-RH) provide evidence for a hypothalamic basis for this disorder. Additional data are presented indicating that variables such as circulating estrogen levels may influence the gonadotropin response to LH-RH.