Pleuronectiform Fish Research Articles

Age and growth of the red flounder Paralichthys orbignyanus (Teleostei: Pleuronectiformes) in southern Brazil

The red flounder Paralichthys orbignyanus is a large pleuronectiform fish endemic in coastal waters, coastal lagoons and estuaries in the southwestern Atlantic. Although less abundant than other Paralichthys spp, its high price makes it a valuable resource for small-scale fishers that have been intensely fished in the last decades. To study its growth and lifespan in southern Brazil, we examined thin otolith sections collected for age determinations of both young-of-the-year (YOY) and older fishes. Opaque bands form mainly in spring and summer, coincident with the reproductive season. Larger and older males reached 601 mm and eight years, while females reached 985 mm and 11 years. The assumed daily microincrements counts ranged from 127 to 196 for YOY of 135 to 184 mm TL. The common weight-length equation for grouped sexes was TW♀♂=0.000015TL2.93 (mm, g). The von Bertalanffy growth equations were: TL♀=1076(1–e–0.15 (t+0.78)); TL♂=652(1–e–0.28 (t+0.48)); and TL♀♂=839(1–e–0.20 (t+0.67)). Therefore, P. orbignyanus is a fast-growing and relatively short-living species for which females attain larger length and older ages than males, characteristics that have to be taken into account for its stock assessment and management.

Emendation of the genus Neoheterobothrium and a proposal of a new genus Paraheterobothrium (Monogenea: Diclidophoridae) for five species of diclidophorids from Pleuronectiform fishes.

Neoheterobothrium chilense González, Oliva & Acuña, 2002 is redescribed based on newly collected specimens from the type host, Hippoglossina macrops and type locality (Coquimbo, Northern Chile). Type specimens of Neoheterobothrium hippoglossini Piasecki, Wierzbicka & Kempter, 2000 and Choricotyle exilis Crane, 1972 are also redescribed. These three diclidophorid monogeneans infecting pleuronectiform flatfishes have pre-ovarian seminal receptacle, ootype inside the semicircle of ovary and elongated pharynx, differentiated from the most similar Orbocotyle Euzet & Suriano, 1975 in that members of the latter genus possess post-ovarian seminal receptacle, post-ovarian ootype and cylindrical or pyriform pharynx. Paraheterobothrium n. g. is proposed for P. chilense n. comb. (type), P. hippoglossini n. comb., P. exilis n. comb., P. papillosum n. comb. and P. syacii n. comb. A redescription of Neoheterobothrium affine (Linton, 1898), the type species of the genus, based on voucher specimens confirmed differences from the new genus in the presence of lamellate plate in the anterior jaw of clamps, absence of seminal receptacle and ovoid pharynx. The genus Neoheterobothrium was emended and N. cynoscioni (MacCallum, 1917) and N. mcdonaldi Payne, 1987 were removed from the genus. Neoheterobothrium now comprises N. affine (type), N. insulare Oliva & Luque, 1995, N. hirame Ogawa, 1999, and N. paralichthyi Suriano & Labriola, 1999, all of them parasites of flatfishes of the genus Paralichthys. Molecular analyses with the internal transcribed spacer 1 distinguished the clade for Paraheterobothrium spp. (P. chilense n. comb. and P. papillosum n. comb.) and Neoheterobothrium spp. (N. hirame, N. affine and N. paralichthyi), supporting this taxonomic emendation.

The residency, movement patterns and habitat association of several demersal fish species to the Orange County Sanitation District wastewater outfall

Abstract Wastewater outfall pipes are structures that may attract marine fishes, yet previous studies that address the risks of exposure to wastewater effluent rarely account for the movements of the species studied. This study used acoustic telemetry to quantify the movement patterns and habitat association of demersal species (Citharichthys sordidus, Pleuronichthys verticalis, Parophrys vetulus, Sebastes miniatus) at two sites (near a wastewater outfall and at a reference site) in southern California over one year. Residencies to both sites were low for pleuronectiform fishes (C. sordidus, P. verticalis, P. vetulus, less than 10% of the study duration was spent in either site), which indicates that tissue samples from these species likely reflect the accumulation of contaminants across individuals’ ranges, not just the outfall site. Alternatively, S. miniatus showed higher degrees of residency to the outfall site (nearly 40% of the study duration) and may be the most susceptible to wastewater effluent effects.

External Asymmetry and Pectoral Fin Loss in the Bamboo Sole (Heteromycteris japonica): Small-Sized Sole with Potential as a Pleuronectiformes Experimental Model.

Pleuronectiform fish develop marked external asymmetry in eye location and skin color at metamorphosis. The bamboo sole, Heteromycteris japonica, also exhibits loss of the pectoral fins at metamorphosis. Because of its small body size, short generation time, and long spawning season, we focused on the bamboo sole as an experimental model to investigate metamorphic asymmetry and pectoral fin loss during development. In the present study, we utilized a small-scale culture system to evaluate bamboo sole larvae and larval development, and a microinjection system for fertilized eggs. The culture system described here uses an 18 L culture tank for rotifers (the first diet for larvae) and 5 L plastic beakers for larval culture. Under this system, most larvae completed metamorphosis, including one-eye migration and pigmentation of the ocular side, by 23 days postfertilization (dpf) at 25°C. Larvae at density of 120-150 per liter were grown from hatching to 23 dpf with a survival ratio of 60-75% per beaker. Pectoral fins, including coracoid and disk cartilage, formed but were completely lost in late metamorphosis without formation of proximal radials and fin rays. The microinjection system designed here is adequate for the bamboo sole and allows injection of 100 one-cell-stage embryos per day. We expect that the culture and microinjection systems described here will facilitate the use of the bamboo sole as an experimental model organism in developmental biology.

Ecotoxicity and genotoxicity of cadmium in different marine trophic levels

Cadmium ecotoxicity and genotoxicity was assessed in three representative species of different trophic levels of marine ecosystems – the calanoid copepod Acartia tonsa, the decapod shrimp, Palaemon varians and the pleuronectiform fish Solea senegalensis. Ecotoxicity endpoints assessed in this study were adult survival, hatching success and larval development ratio (LDR) for A. tonsa, survival of the first larval stage (zoea I) and post-larvae of P. varians, egg and larvae survival, as well as the presence of malformations in the larval stage of S. senegalensis. In vivo genotoxicity was assessed on adult A. tonsa, the larval and postlarval stage of P. varians and newly hatched larvae of S. senegalensis using the comet assay. Results showed that the highest sensitivity to cadmium is displayed by A. tonsa, with the most sensitive endpoint being the LDR of nauplii to copepodites. Sole eggs displayed the highest tolerance to cadmium compared to the other endpoints evaluated for all tested species. Recorded cadmium toxicity was (by increasing order): S. senegalensis eggs < P. varians post-larvae < P. varians zoea I < S. senegalensis larvae < A. tonsa eggs < A. tonsa LDR. DNA damage to all species exposed to cadmium increased with increasing concentrations. Overall, understanding cadmium chemical speciation is paramount to reliably evaluate the effects of this metal in marine ecosystems. Cadmium is genotoxic to all three species tested and therefore may differentially impact individuals and populations of marine taxa. As A. tonsa was the most sensitive species and occupies a lower trophic level, it is likely that cadmium contamination may trigger bottom-up cascading effects in marine trophic interactions.

First record of abnormal body coloration in a rockfish Sebastes trivittatus (Scorpaenoidei: Sebastidae)

Abnormal body coloration (malpigmentation) in teleost fishes usually occurs as either a deficiency (albinism or hypomelanosis) or an excess (melanism or hypermelanosis) of pigmentation (e.g., Simon et al. 2009; Jawad et al. 2013). A particular form of the former, phenotypically expressed as bright yellow or orange body coloration, has been referred to as xanthism or xanthochroism (e.g., Amaoka 1995; Carson 2011; Lewand et al. 2013). Although malpigmentation in teleosts has been extensively studied in the context of aquaculture, especially in Pleuronectiform fishes in relation to developing asymmetry (e.g., Matsumoto and Seikai 1992; Venizelos and Benetti 1999; Burton 2010), it has been largely overlooked in natural populations. Abnormal coloration in rockfishes of the genus Sebastes has occasionally been reported, mostly from the eastern North Pacific (e.g., Phillips 1957, 1964; reviewed in Love et al. 2002). However, most of these were considered to have been caused by skin tumors, resulting in black patches on the body, with other color abnormalities having been relatively rarely documented [Love et al. 2002; but see Muto et al. (2013) for partial albinism; Lewand et al. (2013) for xanthochroism]. On 7 July 2014, a single individual of Sebastes trivittatus, exhibiting a rare example of abnormal body coloration, was captured by gill net at a depth of 17 m, near Daikokujima Island, off Muroran, Hokkaido, Japan (Fig. 1a). A brief description of the specimen is given below. Morphological characters were examined following Muto et al. (2011). The terminology of the head spines followed Randall and Eschmeyer (2001). The specimen was deposited in the Kyoto University Fish Collection (FAKU). Description (based on FAKU 137112, male, 189.5 mm in standard length). The following measurements are expressed as percentage of standard length: head length 38.2; snout length 9.3; orbit diameter 9.4; interorbital width 4.9; postorbital length 19.9; upper-jaw length 19.5; body width 17.1; body depth 1 35.0; body depth 2 26.9; caudal-peduncle depth 9.6; upper-peduncle length 10.8; lower-peduncle length 18.6; dorsal-fin base length 60.9; spinous dorsal-fin base length 37.2; soft dorsal-fin base length 24.2; anal-fin base length 15.3; preanal length 65.4; predorsal length 34.7; prepelvic length 41.7; first dorsal-fin spine length 7.1; second dorsal-fin spine length 11.6; third dorsal-fin spine length 17.0; fourth dorsal-fin spine length 19.5; fifth dorsal-fin spine length 19.9; antepenultimate dorsal-fin spine length 11.8; penultimate dorsal-fin spine length 9.9; last dorsal-fin spine length 12.2; first anal-fin spine length 8.2; second anal-fin spine length 16.5; third anal-fin spine length 15.3; longest (second) anal-fin soft ray length 19.9; pectoral-fin length 30.1; pelvic-fin length 25.2; pelvic-fin spine length 14.7. Dorsal-fin rays XIII, 13; anal-fin rays III, 6; pectoral-fin rays 18, uppermost ray unbranched, second to ninth Electronic supplementary material The online version of this article (doi:10.1007/s10228-015-0471-x) contains supplementary material, which is available to authorized users.

A diverse Eocene fish scale assemblage from Seymour Island, Antarctica

A collection of fish scales from the La Meseta Formation (Paleogene, Eocene; Seymour Island, Antarctica) has been studied, permitting the characterisation of five clearly distinguishable morphotypes. Three morphotypes are comparable to scales of recent trachichthyids, clupeids, and gadids. The other two morphotypes are represented only by two poorly preserved specimens; however, they probably pertain to perciform and pleuronectiform fishes. The latter is a new record for the La Meseta Formation. The mixed composition of the fish scale assemblage reflects substantial redistribution of fish remains within a high-energy, shallow marine environment. Scales were recovered from calcareous sandstone concretions, which accounts for their overall good preservation. This is the most diversified assemblage of fish scales yet reported from the fossil record of Antarctica.

Interaction of orexin/hypocretin-like immunoreactive neurons with melanin-concentrating hormone and α-melanocyte-stimulating hormone neurons in brain of a pleuronectiform fish, barfin flounder

Immunohistochemical localization of orexin/hypocretin in the brain of a pleuronectiform fish, the barfin flounder Verasper moseri was examined as the first step in unraveling the possible function of the hormone in the brain. Orexin-A-like immunoreactive (ir) cell bodies were found to be located in the nucleus posterioris periventricularis (NPPv) of the hypothalamus, and orexin-A-like-ir fibers were detected not only in the hypothalamus but also extensively throughout the brain. The orexin-A-like-ir cell bodies did not project their fibers to the pituitary gland. Since melaninconcentrating hormone (MCH) and α-melanocyte-stimulating hormone (α-MSH) are suggested to regulate food intake in addition to orexin/hypocretin in the teleost fish, it was examined whether neural connections exist between orexin neurons and the MCH and α-MSH neurons in the barfin flounder brain by using double-staining immunohistochemistry. Some orexin-A-like-ir fibers were in close contact with the MCH-ir and α-MSH-ir cell bodies in the hypothalamus. Moreover, a few MCH-ir and α-MSH-ir fibers were in close contact with the orexin-A-like-ir cell bodies in the hypothalamus. These results suggest that reciprocal connections exist between the orexin and MCH neurons and between the orexin and α-MSH neurons in the brain of the barfin flounder.

A new Western Pacific Tonguefish (Pleuronectiformes: Cynoglossidae): The first Pleuronectiform discovered at active Hydrothermal Vents

Symphurus thermophilus n. sp., described from 16 specimens collected by submersibles, ROV, epibenthic sled and dredge, occurs on a variety of substrata at several active hydrothermal sites located at 239–733 m between 21°N and 35°S in the western Pacific Ocean. Symphurus thermophilus, the only pleuronectiform fish known to inhabit hydrothermal vent areas, is characterized by the combination of a 1–2–2–2–2 pattern of interdigitation of dorsal proximal pterygiophores and neural spines, 14 caudal-fin rays, 5 hypurals, 9 abdominal vertebrae, 47–51 total vertebrae, 88–94 dorsal-fin rays, 74–80 anal-fin rays, 100–112 scales in longitudinal series, ocular-side pigmentation pattern featuring 5–8, black, mostly incomplete crossbands, uniformly white blind side, and black peritoneum. Of specimens examined, seven including the holotype, were collected on Kaikata Seamount off southern Japan; one specimen was collected at the Kasuga-2 hydrothermal vent, Marianas Islands; and six were collected at sites on the Kermadec Ridge. In addition to specimens captured, many other S. thermophilus were observed from submersibles and ROVs at hydrothermal sites in the western Pacific including those in the Marianas Islands, at Nikko Seamount near Minami-Iohjima Island, and at Minami-Ensei Knoll, Mid-Okinawa Trough. Many of the specimens examined have skeletal anomalies including fused bones in the caudal skeleton, and missing or partially developed and/or misshapen fin rays.

Evidence for positive Darwinian selection on the hepcidin gene of Perciform and Pleuronectiform fishes

Hepcidin is a small cysteine-rich peptide that plays an important role in antimicrobial activity and in maintaining iron homeostasis in vertebrates. Here we report on the underlying mechanism that maintains high sequence diversities among the hepcidin-like variants of perciform and pleuronectiform fishes. In contrast to mammals, maximum likelihood-based codon substitution analyses revealed that positive Darwinian selection (nonsynonymous to synonymous substitution, omega > 1) is the likely cause of accelerated rate of amino acid substitutions in the hepcidin mature peptide region of these fishes. Comparison of models incorporating positive selection (omega > 1) at certain sites with models not incorporating positive selection (omega < 1) failed to reject (p = 0) the evidence of positive selection among the codon sites of percifom and pleuronectiform hepcidin. The adaptive evolution of this peptide in perciform and pleuronectiform fishes might be directed by pathogens when the host is exposed to new habitats/environments.

Melanocyte-stimulating hormone facilitates hypermelanosis on the non-eyed side of the barfin flounder, a pleuronectiform fish

A pleuronectiform fish, the barfin flounder, Verasper moseri, is promising for aquaculture and resource enhancement in Northern Japan due to its high commercial value. Hypermelanosis of its non-eyed side, which frequently occurs under culture conditions, diminishes its commercial value. Two peptide hormones, melanin-concentrating hormone (MCH) and melanocyte-stimulating hormone (MSH), having opposing actions, are associated with the color changes of fish. We have previously reported the positive effect of MCH in preventing hypermelanosis. Here, we examined the effects of MSH on the occurrence of hypermelanosis. A single injection of Des-Ac-α-MSH [0.01 nmol/g–10 nmol/g (0.016 μg–16 μg/g)] did not change the eyed-side body color, while a single injection of MCH [0.1 nmol/g (0.21 μg/g)] made the eyed-side color paler. No difference was observed in eyed-side lightness between fish injected with MCH (0.1 nmol/g) and those receiving MCH (0.1 nmol/g) and an increased amount of Des-Ac-α-MSH (0.01 nmol/g–10 nmol/g) simultaneously. These results indicate that MSH does not suppress the in vivo body color-paling effects of MCH in barfin flounders. On the other hand, implantation of a cholesterol pellet containing Des-Ac-α-MSH (280 μg, twice at 29-day interval) increased hypermelanosis of the non-eyed side of barfin flounders compared to control fish. Eyed-side bodies of MSH-treated fish were darker than control fish; thus, MSH is involved in morphological color change including ectopic melanin synthesis in non-eyed-side skin.

Self-feeding activity of a pleuronectiform fish, the barfin flounder

The self-feeding activity of the barfin flounder ( Verasper moseri) was examined under natural photoperiod and temperature. The experiment, carried out over 12 weeks from September to December, involved tagged fish (mean body weight: 371 g) reared in three 1000-l tanks (3 or 5 fish per tank) with a self-feeder device. The sensor comprised a switch and trigger string with a bead. Self-feeding activity was recorded in all tanks from day 1. The fish fed mostly at night. Strong positive correlations were observed between the number of daily feeder activations and water temperature/photoperiod, and all fish grew during the experiment. These results demonstrate that barfin flounder can operate self-feeding systems and it is suggested that self-feeding activity is influenced by photoperiod and water temperature.

Spatial and temporal changes of coastal demersal assemblages in the Gulf of Cadiz (SW Spain) in relation to environmental conditions

Abstract Changes in space and time in “global values” (numerical abundance, biomass, diversity ( H ′, Shannon–Wiener), number of species ( S )) and in the structure of demersal assemblages were studied in a coastal fringe of the Gulf of Cadiz between the Guadiana and the Guadalquivir rivers. Further, the seasonal patterns in length–frequency histograms and the percentage of juveniles of 10 selected species were calculated based on literature data on length at first maturity ( L m ). Twenty-four successive monthly demersal fishery surveys were conducted between March 2002 and February 2004 at eight fixed stations between 5 and 30 m depth, from which 175 hauls were analysed. Fifty-seven taxa belonging to four orders of fish, cephalopods and crustaceans were selected for analysis. Environmental characterisation included the variables depth, sediment type, bottom temperature (BT), total bottom chlorophyll (BChl), and bottom suspended solids (BSS). Relationships among environmental variables as well as their spatial and temporal changes were explored through Spearman rank correlation ( R s ) and Kruskall–Wallis tests. Their relation to global values was assessed through R s . Differences in global values with respect to space (station) and time (year and season) was assessed through ANOVA techniques via GLM. Spatial and temporal differences in demersal structure were analysed through different multivariate routines from PRIMER including between-matrix correlation analysis (RELATE), analysis of similarities (ANOSIM), species contributions to similarity/dissimilarity (SIMPER), non-metric multidimensional scaling (MDS) and group-average cluster analysis. The degree of match between species-similarity matrices (Bray–Curtis, root–root transformed) and environmental similarity matrices (Euclidean distance) was assessed through the BIO-ENV approach also from PRIMER. Individual R s correlations between selected species and environmental variables also were performed at each station. A strong spatial gradient related to depth, sediment type, and BT (all related to the distance from the Guadalquivir River mouth) was responsible for most of the explained variability in global values and demersal species structure. The shallowest stations, also close to the Guadalquivir River mouth, showed higher numerical abundance and biomass values, and lower H ′ and S values. Typical or abundant species from those stations included fishes from the families Sparidae (particularly Diplodus bellottii ), Haemulidae, Soleidae or the stomatopod Squilla mantis . Some small pelagics like Engraulis encrasicolus were also important at those stations, although were excluded from the analyses to reduce bias. Northwestern deeper stations were defined by higher relative densities of cephalopods and several pleuronectiform fish. Significant seasonal differences in the abundance of several species also were observed at most stations, mainly between summer and winter. Species like Merluccius merluccius were particularly abundant in winter, whereas Arnoglossus laterna was more abundant in summer. Length–frequency analyses showed that changes in abundance were, in many cases, related to the massive appearance of small individuals in the area. Juvenile stages were observed either exclusively or temporally for many of the analysed taxa, revealing the high importance of this zone as a nursery.

Effects of tank color on melanin-concentrating hormone levels in the brain, pituitary gland, and plasma of the barfin flounder as revealed by a newly developed time-resolved fluoroimmunoassay

A pleuronectiform fish, the barfin flounder Verasper moseri, reared in a white tank had a smaller ratio of pigmented area of the skin on non-eyed side, grew faster, and had greater melanin-concentrating hormone (MCH)-immunoreactive cell bodies and MCH gene expression in the brain than in the black tank, indicating that synthesis and release of MCH are higher in fish from a white tank. In the present study, a time-resolved fluoroimmunoassay for MCH was developed. MCH levels were assessed in the brain, pituitary gland, and plasma of barfin flounders reared in a white or black tank. A competitive assay using two antibodies was performed among secondary antibodies in the solid phase, MCH antibodies, samples, and europium-labeled MCH. Displacement curves of serially diluted extracts (brain, pituitary gland, and plasma) of the barfin flounder paralleled that of the MCH standard. MCH levels in the brain and plasma were higher in fish reared in the white tank for 5 months than in the black tank. These results suggest that synthesis and secretion of MCH are enhanced with the white background and that MCH is involved in both somatic growth and the skin pigmentation in the barfin flounder.

Immunocytochemical localization and ontogenic development of ?-melanocyte-stimulating hormone (?-MSH) in the brain of a pleuronectiform fish, barfin flounder

Alpha-melanocyte-stimulating hormone (alpha-MSH) is a pituitary hormone derived by post-translational processing from proopiomelanocortin and is involved in background adaptation in teleost fish. It has also been reported to suppress food intake in mammals. Here, we examined the immunocytochemical localization of alpha-MSH in the brain and pituitary of a pleuronectiform fish, the barfin flounder (Verasper moseri), as a first step in unraveling the possible function of alpha-MSH in the brain. The ontogenic development of the alpha-MSH system was also studied. In the pituitary, alpha-MSH-immunoreactive (ir) cells were preferentially detected in the pars intermedia. In the brain, alpha-MSH-ir neuronal somata were located in the nucleus tuberis lateralis of the basal hypothalamus, and alpha-MSH-ir fibers were located mainly in the telencephalon, hypothalamus, and midbrain. Alpha-MSH-ir neuronal somata did not project their axons to the pituitary. The alpha-MSH-ir neurons differed from those immunoreactive to melanin-concentrating hormone. Alpha-MSH cells in the pituitary and alpha-MSH-ir neuronal somata in the brain were first detected 1 day and 5 days after hatching, respectively. The distribution of alpha-MSH-ir cells, neuronal somata, and fibers showed a pattern similar to that in adult fish 30 days after hatching. These results indicate that the functions of alpha-MSH in the brain and pituitary are different and that alpha-MSH plays physiological roles in the early development of the barfin flounder.

White background reduces the occurrence of staining, activates melanin-concentrating hormone and promotes somatic growth in barfin flounder

A pleuronectiform fish, the barfin flounder, Verasper moseri, is promising for aquaculture and resource enhancement in Northern Japan due to its high commercial value. A major problem in the aquaculture is staining (pigmentation of the skin on non-eyed side) under culture conditions since it diminishes the commercial value of the fish. Melanin-concentrating hormone (MCH) is a peptide hormone produced in the hypothalamus which turns the body of teleosts pale. Here, we examined the employment of MCH to prevent staining. Bolus injection of MCH (1 μg/g body weight (BW)) in barfin flounder turned the stained area pale. The occurrence of staining was suppressed by injection of MCH (1 μg/g BW, once a week, total 10 times). These results indicated that MCH affected the non-eyed side color in addition to the physiological color change on the eyed side. Then, we prepared juvenile fish having no staining by rearing with a tank containing Microceramic on the bottom and transferred them to white, yellow, or black tanks without Microceramic. Eight months later, the percent area of each fish that is stained in white or yellow tanks was significantly smaller than that of fish reared in a black tank. The number of MCH-immunoreactive cell bodies in the brain was significantly greater in the white tank fish than that of the black tank fish, suggesting that white background enhanced the secretion of endogenous MCH, by which occurrence of staining was prevented. Interestingly, both the total length and body weight of the white-reared fish were greater than those of the black-reared fish, respectively. The enhanced production of MCH might augment the food intake of barfin flounders as in mammals, so that the somatic growth of the fish is promoted.

Effects of photoperiod on gonadotropin-releasing hormone levels in the brain and pituitary of underyearling male barfin flounder

: A pleuronectiform fish, the barfin flounder Verasper moseri, expresses three gonadotropin-releasing hormone (GnRH) forms in the brain: salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and seabream GnRH (sbGnRH). To clarify the effects of photoperiod on GnRH systems, changes in brain and pituitary GnRH peptide levels were examined using time-resolved fluoroimmunoassays. In experiment 1, 5-month-old male barfin flounder (mean total length 9.0 cm, body weight 11.0 g) were divided into short (8:16 h light : dark [L:D] cycle; lights on 08.00–16.00 hours) and long photoperiod (16:8 h L:D cycle; lights on 04.00–20.00 hours) groups in mid September and maintained until November under natural water temperature (19.3–15.2°C). Brain sGnRH concentrations were significantly higher in the 16:8 h L:D group than in the 8:16 h L:D group, whereas no significant differences were observed in total length, body weight, plasma testosterone concentration, brain cGnRH-II concentration and pituitary sbGnRH content. In experiment 2, 7-month-old male barfin flounder (mean total length 16.5 cm, body weight 76.8 g) were divided into short and long photoperiod groups in mid December and maintained until February under natural water temperature (12.5–6.6°C). Total length, body weight and condition factor were significantly greater in the 16:8 h L:D group than in the 8:16 h L:D group, whereas no significant differences were observed in plasma testosterone concentration and GnRH levels in the brain and pituitary. These results indicate that levels of sGnRH in barfin flounder are influenced by photoperiodic treatment dependent on water temperature and/or body size.

Two Species of Trichodina (Ciliophora: Peritrichida) from Cultured Flatfishes (Pleuronectiformes) in Atlantic Canada

Air-dried smears of trichodinids were collected from cultured marine flatfishes of the families Pleuronectidae and Scophthalmidae at 2 localities in Atlantic Canada and stained using Klein's dry-silver impregnation technique to reveal the morphology of the adhesive disk. Two species were identified: Trichodina jadranica from the skin of captive broodstock of Pleuronectes americanus, Limanda ferruginea, Hippoglossus hippoglossus, and Scophthalmus aquosus and Trichodina hippoglossi from the skin of juvenile and broodstock H. hippoglossus. The former parasite has an extensive distribution in marine seas worldwide and has broad host specificity. The latter parasite is known only from the North Atlantic Ocean and has been found only on H. hippoglossus. This study represents the first confirmed identifications of Trichodina from pleuronectiform fishes in Atlantic Canada and the first reports of these species in Canadian waters.

GnRH systems in masu salmon and barfin flounder

Multiple forms of the gonadotropin-releasing hormone (GnRH) exist in teleost fish. A salmonid fish, masu salmon Oncorhynchus masou has salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II). sGnRH neurons were scattered from the olfactory nerve through the ventral telencephalon (VT) and the preoptic area (POA). sGnRH but not cGnRH-II was detected in the pituitary. sGnRH mRNA levels in the VT and the POA increased during gonadal maturation, suggesting that sGnRH neurons in these areas are involved in gonadal maturation. sGnRH neurons were first detected in a cluster near the olfactory epithelium 40 days after fertilization. sGnRH neurons were not detected in the brain by the olfactory epithelia lesion, suggesting that sGnRH neurons are derived from the olfactory epithelium. A pleuronectiform fish, barfin flounder Verasper moseri has sGnRH, cGnRH-II and seabream GnRH (sbGnRH). sGnRH and cGnRH-II-immunoreactive fibers were observed throughout the brain, but not in the pituitary. sbGnRH neurons were located in the POA and sent fibers to the pituitary, indicating that sbGnRH is involved in GTH secretion. Judging from the location of neuronal somata and their projections, it is indicated that three GnRH systems exist in the barfin flounder; the TN-, the MT- and the POA-GnRH system. However, in masu salmon, clear anatomical identification of the TN- and the POA-GnRH system is difficult, because the GnRH neurons located in the ventral forebrain are consecutive and the GnRH form produced in these neurons is the same (sGnRH). Thus, it is suggested in masu salmon that sGnRH neurons are derived from the olfactory epithelium, migrate into the brain and play different roles according to the location in the brain.

Immunocytochemical localization and ontogenic development of melanin-concentrating hormone in the brain of a pleuronectiform fish, the barfin flounder.

Melanin-concentrating hormone (MCH) was first discovered in the pituitary of chum salmon because of its role in the regulation of skin pallor. Later, it was found that MCH could also play a role as a central neurotransmitter or neuromodulator in the brain. However, knowledge of the function of MCH in fish has been restricted to certain fish species. Therefore, in the present study, the immunocytochemical localization and ontogenic development of MCH in the brain of a pleuronectiform fish, the barfin flounder Verasper moseri, were examined to obtain a better understanding of this hormone. In adult barfin flounder, MCH-immunoreactive (ir) neuronal somata were most prevalent in the magnocellular neurons of the nucleus tuberis lateralis (NLT), which project to the pituitary. In the pituitary, MCH-ir fibers were distributed in the neurohypophysial tissues within the pars intermedia and, to a lesser extent, into the pars distalis. MCH-ir neuronal somata were also present in dorsally projecting parvocellular neurons, located more posteriorly in the area above the lateral ventricular recess (LVR). LVR-MCH neurons did not seem to project to the pituitary. In the brain, MCH-ir fibers were detected not only in the hypothalamus but also in areas such as the optic tectum and thalamus. MCH-ir neuronal somata and fibers were not detected on the day of hatching. MCH-ir neuronal somata and fibers were first detected in the hypothalamus and the pituitary, respectively, 7 days after hatching. Subsequently, MCH-ir neuronal somata were observed in the NLT and in the area above the LVR 14 days after hatching. The distribution of MCH-ir neuronal somata and fibers showed a pattern similar to that in the adult fish 35-42 days after hatching. These results indicate that MCH neurons were located in the NLT and in the area above the LVR and that NLT-MCH neurons project to the pituitary. MCH neurons were first detected 7 days after hatching, suggesting that MCH plays some physiological role in the early development of barfin flounder.