Opercular Cavity Research Articles

Morphology of the Buccal and Opercular Sealing Apparatus in Mudskippers (Gobiidae: Oxudercinae)

Although possession of the large bucco-opercular cavity and its utilization in the feeding, breathing, egg brooding, and burrowing activities are quite obvious in mudskippers, the apparatus of this structure is little known. In the present study, we examined the anatomy of the bucco-opercular sealing apparatus of four oxudercine gobies, Oxuderces nexipinnis, Scartelaos histophorus, Boleophthalmus boddarti, and Periophthalmodon septemradiatus, showing different degrees of terrestriality. The results show that the morphological modifications including the short and restricted gill openings, the membranes on the gill opercular edge (except O. nexipinnis), and the developed hyohyoideus 3 could serve to seal the gill openings. The possible movement of the ceratohyal, the relative height of the urohyal, and the developed geniohyoideus could function to seal the mouth. Contraction of the hyohyoideus 1 to 3 could compress the opercular cavity generating strong mud spitting, whereas activation of the dilator opercula, levator opercula, and a portion of the geniohyoideus may serve to expand this cavity enable sucking mouthful of water at slow speed. These morphological modifications are presumable to facilitate vital activities of mudskippers as transition onto land.

Molecular and Morphological Characterizations of the Fish Parasitic Isopod Mothocya parvostis (Crustacea: Cymothoidae) Parasitizing Optional Intermediate Hosts: Juveniles of the Cobaltcap Silverside Hypoatherina tsurugae and Yellowfin Seabream Acanthopagrus latus.

Mothocya parvostis (Isopoda: Cymothoidae) is a parasitic crustacean that infests the opercular cavities of fishes. Its main final host is the Japanese halfbeak, Hyporhamphus sajori. However, M. parvostis also infests the black sea bream, Acanthopagrus schelgelii, as an optional intermediate host. Understanding the use of optional intermediate hosts is important for understanding the life history of Cymothoidae, and further information should be obtained. In this study, we aim to investigate the life cycle of M. parvostis. We collected and examined 20 mancae and 144 juveniles of M. parvostis from 129 cobaltcap silversides, Hypoatherina tsurugae, and 494 yellowfin seabreams, Acanthopagrus latus. Molecular analysis of the cytochrome c oxidase subunit I gene and 16S rRNA genes revealed that cymothoid mancae and juveniles from the two fish species were identified to be M. parvostis. All M. parvostis on H. tsurugae and A. latus might be mancae or juveniles, with no adult parasites; thus, H. tsurugae and A. latus juveniles were optional intermediate hosts of M. parvostis. In the results of morphological description, M. parvostis juveniles infesting the final host H. sajori lacked swimming setae, while juveniles parasitizing the two optional intermediate hosts had them. Mothocya parvostis mancae infested juveniles of both species just after metamorphosis, grew with the host. As the fish grows further, the parasite detached from the fish. The parasitic status of M. parvostis in the three optional intermediate hosts indicated that M. parvostis likely reproduced from June to December, and different optional intermediate hosts were used depending on the time of year in Hiroshima Bay. Therefore, a parasitic strategy involving optional intermediate hosts might increase the infestation success of M. parvostis to H. sajori.

Persistent companionships: The parasitic copepod community of the dolphinfishCoryphaena hippuruson the Ecuadorian coast

The common dolphinfish, Coryphaena hippurus, is an important and widespread fishing resource in tropical and subtropical latitudes. It harbors a diverse array of parasitic copepods, but data on their infection indices are quite limited worldwide. We analyzed its parasitic copepod community and infection indices based on the examination of 615 individuals of C. hippurus landed monthly on the coast of Ecuador, over a period of 1 year. Both the opercular cavities and gills of the sampled fish were examined for parasitic copepods, of which nine taxa were recorded: Brachiella quaternia, Caligus belones, C. bonito, C. coryphaenae, C. productus, Euryphorus brachypterus, E. nordmannii, Lepeophtheirus sp., and Lernaeenicus sp. The finding of five of these species (i.e., B. quaternia, C. belones, C. productus, E. brachypterus, and E. nordmannii) represents new geographic records. C. bonito showed the highest prevalence (83%), mean abundance (5.46 ± 4.99), and mean intensity (6.57 ± 4.99), followed by B. quaternia (prevalence = 32%, mean abundance = 1.89 ± 5.66, mean intensity = 5.89 ± 5.71). The infection indices of C. bonito decreased with increasing host length and were higher in females than in males. The parasitic copepod community of common dolphinfish in this study was similar to communities in other parts of its geographic distributional range, including the Atlantic Ocean, the Mediterranean Sea, and the Eastern Pacific, consistently dominated by a generalist parasitic species. This is the first and most detailed quantitative evaluation of the parasitic copepods associated with the dolphinfish and updates the extant parasitological data for this host.

Phenomenon of the complete suppression of cardiac activity in the Black Sea scorpionfish Scorpaena porcus (Scorpaenidae) during an alertness reaction

Teleosts serve as experimental models for the physiological and pathophysiological processes investigation, in particular those related to the heart work. Methods allowing to analyze the frequency parameters of the heart functioning over a long period of time require taking into account the peculiarities of fish behavioral reactions, that can affect the results of the experiment. The aim of this study was to examine the effect of the simplest test loading (sound stimulus) on the frequency parameters of the heart activity recorded by the fiber-optic method. The objects of the study were adults of Scorpaena porcus (12–15 cm long, 80–120 g in weight). In the course of experiments, each scorpionfish was kept in a separate aquarium with seawater (400×400×350 mm), with constant temperature (21 ± 0.5) °C and given oxygen content (5.5–6.7 mg·L−1, normoxia). The heart rate (HR) recording was carried out by an invasive fiber-optic method, the essence of which is to transmit the radiation of the infrared semiconductor laser of the photoplethysmograph through a thin fiber-optic cable to the pericardial membrane of the heart and then to fix the signal reflected from the contracting myocardium in the photodetector. During implantation of the photoplethysmograph light guides, the fish were anesthetized by placing them in an anesthetic solution (urethane, 2.4 g·L−1 of seawater). In the fornix of the opercular cavity above the area of the conditional heart projection, a minimal dissection of the lining epithelium was performed, through which the underlying tissues were sequentially separated by a blunt method until the pericardial membrane was reached without breaking it. Through the lumen formed in the tissues, two optical light guide sensors were introduced to the surface of the pericardial membrane. Further, free-swimming scorpionfish participated in the experiment after a day of rehabilitation after the surgery. Additionally, we assessed the functional state of the animals by visual fixation of respiratory activity by the quantity of movements of the opercular covers per minute. During studying the test loading effect on the correct registration of the scorpionfish HR, the phenomenon of temporary complete suppression of cardiac activity was revealed, which manifested itself upon presentation of sound stimuli (alertness, “freezing” reaction). The duration of cardiac arrest was 31 to 50 seconds; it was accompanied by the cessation of movement of the opercular covers (respiratory arrest, apnea). During the restoration of cardiac activity, two types of physiological reactions were noted. The first type of recovery reaction was characterized by a simultaneous 1.5-fold increase in the HR and a 2-fold enhancement in the photoplethysmograph signal amplitude. The second type of reaction was accompanied by a rise in the HR by 22 % (p < 0.05) against the backdrop of a decrement in the signal amplitude of the photoplethysmograph sensors by 28 % (p < 0.05); within 120 seconds, the scorpionfish HR returned to baseline. It is assumed that the short-term delay in the scorpionfish cardiac activity is based on the phenomenon of cardiorespiratory coupling and synchronization. The behavioral reaction in the form of suppression for the cardiac and simultaneously respiratory activity generation ensures the complete absence of acoustic and electrical signals, which unmask an ambush predator location, and contributes to the scorpionfish survival.

The Amazonian fish Colossoma macropomum harbors high myxosporean diversity: A description of three novel species from a fish farm

The farming of Colossoma macropomum has intensified in recent years, leading to an increased need for research into the health of the fish. We therefore investigated the diversity of myxosporeans (Cnidaria: Myxozoa) infecting C. macropomum in a breeding system in the municipality of Rio Branco, in the state of Acre, Brazil. Twenty-four fish specimens were examined from June to August 2018. Our results revealed a high prevalence of infection, with 23 specimens (95.8%) exhibiting myxosporean plasmodia. Morphological analysis, based on light and electron microscopies, and molecular analysis (small subunit ribosomal DNA [SSU rDNA] sequencing) revealed the occurrence of three novel species of the genus Myxobolus. Plasmodia of Myxobolus guttae n. sp. were found in the fins of 75% of the specimens, and the myxospores were pear-shaped, measuring 12.3 ± 0.6 (10.3–13.5) μm in length, 8.1 ± 0.3 (7.1–8.6) μm in width, and 5.1 ± 0.6 (4.5–6.5) μm in thickness. The polar capsules were elongated and equal in size, measuring 6.8 ± 0.5 (5.8–7.6) μm in length and 2.5 ± 0.3 (1.8–3.1) μm in width, exhibiting polar tubules with 9–10 coils. The plasmodia of Myxobolus longus n. sp. were found in the gills of 45.8% of the C. macropomum specimens, and the myxospores were fusiform, measuring 16.4 ± 0.6 (14.7–17.3) μm in length, 7.1 ± 0.2 (6.8–7.7) μm in width and 5.5 ± 0.6 (4.4–6.6) μm in thickness. The polar capsules occupied more than half of the myxospore, exhibiting different sizes, the largest measuring 9.2 ± 0.5 (7.3–10.1) μm in length and 2.5 ± 0.3 (2.0–3.1) μm in width, while the smallest measured 8.5 ± 0.4 (7.1–9.1) μm in length and 2.4 ± 0.2 (1.9–3.0) μm in width. Both polar capsules contained polar tubules with 10–12 coils. For Myxobolus tambaquiensis n. sp., plasmodia were found in the opercular cavity of 41.7% of the fish specimens, and the myxospores had an oval shape, measuring 10.0 ± 0.4 (9.5–11.3) μm in length, 6.5 ± 0.2 (6.1–7.1) μm in width, and 4.6 ± 0.4 (3.9–5.6) μm in thickness. The polar capsules were elongated and equal in size, measuring 4.9 ± 0.2 (4.4–5.3) μm in length and 1.9 ± 0.2 (1.5–2.2) μm in width, closing with 8–9 coils of the polar tubule. The morphological and sequencing data of the SSU rDNA showed that the three species studied herein remain unknown to science, increasing the diversity of myxosporeans infecting C. macropomum, an iconic fish in South American freshwater fish farming. The SSU rDNA based phylogenetic analysis revealed that Myxobolus spp. parasites of C. macropomum did not have a monophyletic origin, identifying different times and pathways of the acquisition of parasites by this host species.

The feeding system of Tiktaalik roseae: an intermediate between suction feeding and biting

Changes to feeding structures are a fundamental component of the vertebrate transition from water to land. Classically, this event has been characterized as a shift from an aquatic, suction-based mode of prey capture involving cranial kinesis to a biting-based feeding system utilizing a rigid skull capable of capturing prey on land. Here we show that a key intermediate, Tiktaalik roseae, was capable of cranial kinesis despite significant restructuring of the skull to facilitate biting and snapping. Lateral sliding joints between the cheek and dermal skull roof, as well as independent mobility between the hyomandibula and palatoquadrate, enable the suspensorium of T. roseae to expand laterally in a manner similar to modern alligator gars and polypterids. This movement can expand the spiracular and opercular cavities during feeding and respiration, which would direct fluid through the feeding apparatus. Detailed analysis of the sutural morphology of T. roseae suggests that the ability to laterally expand the cheek and palate was maintained during the fish-to-tetrapod transition, implying that limited cranial kinesis was plesiomorphic to the earliest limbed vertebrates. Furthermore, recent kinematic studies of feeding in gars demonstrate that prey capture with lateral snapping can synergistically combine both biting and suction, rather than trading off one for the other. A "gar-like" stage in early tetrapod evolution might have been an important intermediate step in the evolution of terrestrial feeding systems by maintaining suction-generation capabilities while simultaneously elaborating a mechanism for biting-based prey capture.

Supplemental diagnosis and phylogeny of Myxobolus absonus (Cnidaria, Myxozoa) from the eye of the freshwater fish Pimelodus maculatus (Siluriformes, Pimelodidae)

Myxobolus absonusCellere et al., 2002 was originally described as having free cysts in the opercular cavity of the freshwater fish Pimelodus maculatus in Brazil. The present study provides a supplemental description of this parasite from the eye of its type host, with basis on morphological, ultrastructural, and molecular data of the SSU rRNA gene. The parasite formed spherical whitish cysts, which wall presented numerous microvilli that attached to the collagen layers of the corneal stroma. Myxospores were oval in valvular and sutural view, measuring 13.2 ± 0.4 μm in length, 8.5 ± 0.4 μm in width, and 6.6 ± 0.3 μm in thickness. Two asymmetric pyriform polar capsules were located at the anterior pole: the larger 6.2 ± 0.4 μm long and 3.6 ± 0.3 μm wide, containing a polar filament coiled in 6 turns; and the smaller 3.5 ± 0.3 μm long and 1.9 ± 0.1 μm wide, containing a polar filament coiled in 4 turns. At the posterior pole, the sporoplasm displayed two nuclei and numerous spherical sporoplasmosomes. Phylogenetic analysis using maximum likelihood, Bayesian inference and maximum parsimony revealed M. absonus clustering within a well-supported clade with poorly-resolved internal nodes, amongst the SSU rRNA sequences of other myxobolids that infect siluriform and characiform fish hosts, as well as the perciform-infecting species Myxobolus acanthogobii, Triangula percae and Cardimyxobolus japonensis. This clade appeared separated from the other clades comprising most of the species that infect siluriform and characiform hosts, showing that more than one myxobolid lineage evolved while parasitizing these taxonomic groups of fish.

Nerocila sp. (Isopoda: Cymothoidae) parasitizing Mugil liza (Teleostei: Mugilidae) in São Francisco do Sul, Santa Catarina, Brazil

Isópodes da família Cymothoidae são ectoparasitos de peixes, com baixa especificidade de hospedeiros, comumente encontrados fixados nas brânquias, boca, cavidade opercular, narinas e tegumento de ampla variedade de hospedeiros. Os danos causados são variáveis em função do grau de parasitismo e do sítio de infestação e podem provocar desconforto respiratório nos hospedeiros. O objetivo deste estudo foi relatar a ocorrência do isópode Nerocila sp. Leach, 1818 parasitando Mugil liza Valenciennes, 1836, capturada na Baía da Babitonga, estado de Santa Catarina, Brasil. Uma fêmea de 24 mm de comprimento e 11 mm de largura, contendo ovos de 1.18 ± 0.08 x 1.03 ± 0.06 mm, foi encontrada na nadadeira peitoral de M. liza.

Studies on Parasitic Crustaceans among Some Cultured Marine Fishes in Ismailia Governorate

The present study was conducted on a total of 200 marine fishes (100 of Dicentrarchus labrax and 100 of D.punctatus) collected from different private fish farms in Ismailia Governorate. There were no pathognomonic lesions in the naturally infested fishes except marbling appearance of gills infested by Isopoda. Skin lesions were found in opercular cavities of fishes infested by Isopoda. The main P.M lesions were hemorrhagic areas on EBS and emaciation. Some fishes showed Sea lice in the buccal cavity with ulcerative lesions in the area of attachment. The highest crustacean infestation rate was recorded in Dicentrarchus labrax (75%) followed by D.punctatus (42%). The isolated crustacean parasites from both fish species were copepods (Lernanthropus kroyeri, Caligus minimus and C.longipedis) and Isopods (Nerocila spp., Renocila spp. and Anilocra spp.).Total and Seasonal prevalence of crustacean parasites, histopathological picture and identification of copepod parasites using molecular biology (PCR) were also recorded.

Molecular phylogeny of obligate fish parasites of the family Cymothoidae (Isopoda, Crustacea): evolution of the attachment mode to host fish and the habitat shift from saline water to freshwater

In host–parasite coevolution, parasite innovations including the acquisition of new habitats and novel traits can trigger evolutionary breakthroughs and enhance parasite diversification via accumulation of new hosts. All species of the family Cymothoidae are obligate fish parasites, attaching to exterior body surfaces of fish, the buccal or opercular cavities, or burrowing into abdominal muscle tissue. In the present study, we constructed a molecular phylogeny of 27 cymothoid species that parasitise 38 fish species, combined with 2 prior cymothoid datasets, based on the sequences of mitochondrial 16S rRNA and COI genes. We explored the evolution of the host attachment mode, and the habitat shift from saline water to freshwater. Our evolutionary trees include two freshwater clades, an abdominal burrower clade, and cymothoid clades that are closer to the base of Cymothoidae than those initially analysed. We found that the basal clade of Cymothoidae was Elthusa sacciger, which is parasitic in the opercular cavity of synaphobranchid eels. This result suggests that cymothoids may have originated in deep seas, subsequently expanded to shallow seas, and then to brackish and/or freshwater, by shifting host species. Invasion of freshwater habitats has occurred at least twice; freshwater abdominal muscle burrowers living on armoured catfish constitute a clade allied to E. sacciger. The ancestral host attachment site, based on our dataset, was the opercular cavity, followed (sequentially) by buccal colonisation and attachment to the external body.

A Solution Strategy to Include the Opening of the Opercular Slits in Moving-Mesh CFD Models of Suction Feeding.

The gill cover of fish and pre-metamorphic salamanders has a key role in suction feeding by acting as a one-way valve. It initially closes and avoids an inflow of water through the gill slits, after which it opens to allow outflow of the water that was sucked through the mouth into the expanded buccopharyngeal cavity. However, due to the inability of analytical models (relying on the continuity principle) to calculate the flow of fluid through a cavity with two openings and that was changing in shape and size, stringent boundary conditions had to be used in previously developed mathematical models after the moment of the valve's opening. By solving additionally for the conservation of momentum, computational fluid dynamics (CFD) has the capacity to dynamically simulate these flows, but this technique also faces complications in modeling a transition from closed to open valves. Here, I present a relatively simple solution strategy to incorporate the opening of the valves, exemplified in an axisymmetrical model of a suction-feeding sunfish in ANSYS Fluent software. By controlling viscosity of a separately defined fluid entity in the region of the opercular cavity, early inflow can be blocked (high viscosity assigned) and later outflow can be allowed (changing viscosity to that of water). Finally, by analyzing the CFD solution obtained for the sunfish model, a few new insights into the biomechanics of suction feeding are gained.

Gill monogenean communities on three commercially important sparid fish in Omani waters

The prevalence and intensity of polyopisthocotylean monogeneans on the gills of three commercially important species of sparid caught in Omani coastal waters close to the city port of Muscat were determined and compared. Throughout May 2012 to April 2013, infections on bi-weekly samples of the soldier seabream, Argyrops filamentosus (Valenciennes, 1830), the king soldier seabream, Argyrops spinifer (Forsskål, 1775), and, the silver seabream, Rhabdosargus sabra were evaluated. From a total of 200 specimens (standard length of 26–52 cm), caught by line angling or by traps, at least three species of gill monogenean, namely Omanicotyle [Bivagina] heterospina, Heteromicrocotyla sp. and Microcotyle sp., were commonly encountered. Silver bream, which was infected by all three monogeneans, bore the highest infections (100% prevalence; mean intensity of 20.14 ± 0.92 parasites fish-1), whilst the soldier bream, which was infected only by O. heterospina had the lowest levels of infection (of the three sparids with 63.8% prevalence; mean intensity 5.8 ± 0.17 parasites fish-1). Comments on the distribution of monogeneans on each host are provided but to what extent this is influenced by water current speeds passing through the buccal and opercular cavities, gill morphology, parasite size, and / or the morphology and efficiency of the parasite’s attachment apparatus requires establishing and forms the basis of ongoing investigations.

A new species of Acantholochus (Cyclopoida, Bomolochidae) parasitic on the barred grunt Conodon nobilis (Linnaeus, 1758) (Osteichthyes, Haemulidae) from Rio de Janeiro, Brazil

A new species of Acantholochus Cressey, 1984 (Cyclopoida, Bomolochidae), parasitic on the gills and opercular cavity of the barred grunt Conodon nobilis (Linnaeus, 1758), from the coastal zone of the State of Rio de Janeiro, Brazil, is described and illustrated. The new species differs from its congeners through a combination of characters that includes presence of lamellae on the spines on the third segment of the exopods of the third leg, the number of antennule segments, and the presence of one seta on the second endopodal segment of the third leg.

Sarcoma in the thymus of juvenile meagre Argyrosomus regius reared in an intensive system

Juvenile meagre Argyrosomus regius (Asso, 1809) maintained in experimental conditions developed lateral and/or bilateral circular-shaped sarcoma within the opercular cavity. The sarcoma was dense, reddish and its growth from the branchial arch exerted pressure on the operculum forcing it to open. Histologically, the neoplasm exhibited marked proliferation of mesenchymal connective tissue composed largely of fusiform cells, which developed in a solid pattern accompanied by abundant mononuclear cell types. Multifocal areas of discrete necrosis were also observed, compatible with a sarcomatous proliferation. The immunological parameters analysed suggested an inflammatory response. No bacteria were isolated from the hematopoietic organs. However, Vibrio species, components of the normal seawater flora, were isolated from the tumour, which may have had a role in eliciting the immune response. No evidence of viral pathogens was found by electron microscopy. In order to look for cytogenetic alterations often linked to sarcomas, the diploid number and karyotype of this species were determined for the first time. An increase in the aneuploidy level was observed in sarcoma cell metaphase stages compared to other tissues. The aetiology of this tumour remains unknown.

Respiratory vasculatures of the intertidal air-breathing eel goby, Odontamblyopus lacepedii (Gobiidae: Amblyopinae)

Lacking a propensity to emerge over the mud surface, the eel goby, Odontamblyopus lacepedii, survives low tide periods by continuously breathing air in burrows filled with hypoxic water. As with most marine air-breathing fishes, O. lacepedii does not possess an accessory air-breathing organ, but holds air in the buccal–opercular cavity. The present study aimed to clarify how the respiratory vasculature has been modified in this facultative air-breathing fish. Results showed that the gills apparently lacked structural modifications for air breathing, whereas the inner epithelia of the opercula were richly vascularized. Comparison with two sympatric gobies revealed that the density of blood capillaries within 10μm from the inner opercular epithelial surface in O. lacepedii (14.5 ± 3.0 capillaries mm−1; mean ± s.d., n = 3) was significantly higher than in the aquatic non-air-breathing Acanthogobius hasta (0.0 ± 0.0) but significantly lower than in the amphibious air-breathing mudskipper, Periophthalmus modestus (59.1 ± 8.5). The opercular capillary bed was supplied predominantly by the 1st efferent branchial arteries (EBA1) and drained by the opercular veins, which open into the anterior cardinal vein. Deep invaginations at the distal end of the EBA1 and the junction with EBA2 are suggestive of blood flow regulatory sites during breath-holding and apnoeic periods. It remains to be investigated how blood flow through the gills is maintained during breath holding when the buccal–opercular cavity is filled with air.

Morphological study on the gills of two species of fresh water fishes: Oreochromis niloticus and Clarias gariepinus

The gross and microscopic morphology of the gills of both Nile tilabia (Oreochromis niloticus) and sharptooth catfish (Clarias gariepinus) were described including light and scanning electron microscopy. The anatomical differences between the gill system of the two species were basically related to the geometry of the head and opercular cavities. Each species had four pairs of gills which were connected in a median interbranchial septum. In addition, a fifth rudimentary gill without gill filaments was found in catfish. The lengths and gaps between the gill arches in both species decreased medialwards. The gill rakers of tilabia were generally short and widely spaced compared to the long and narrow spaced rakers of the catfish. The gill filaments and lamellae of tilabia were longer than those of the catfish indicating a greater gill surface area in the former species. The catfish was additionally supplied by modified gills in the form of branched bulbous dendritic structures originating from the second and fourth gill arches. Scanning electron microscopy revealed that the surface of both gill filaments and lamellae was covered by polyhedral cells in tilabia and oval or elongated cells in catfish. These cells carried numerous microplicae which were better developed in tilabia. All gill parts, as revealed by light microscope, were nearly covered by mucous epithelium, however, the mucous cells were present on the lamellae of the catfish only. The rakers of both species demonstrated many taste buds and infiltrating lymphocytes in the epithelial covering. In catfish, in particular, several alarm substance cells were also scattered in this epithelium.

Pseudobranch and gill Na +, K +-ATPase activity in juvenile chinook salmon, Oncorhynchus tshawytscha: developmental changes and effects of growth hormone, cortisol and seawater transfer

The teleost pseudobranch is a gill-like structure often fused to the anterior of the opercular cavity. Pseudobranch cells are mitochondria rich and have high levels of Na +, K +-ATPase activity. In this study, pseudobranch Na +, K +-ATPase activity in juvenile chinook salmon ( Oncorhynchus tshawytscha) was compared to gill Na +, K +-ATPase activity, a known marker of parr–smolt transformation, in three experiments. In two stocks of New Zealand chinook salmon, pseudobranch Na +, K +-ATPase activity was found to significantly increase during development. At these times gill Na +, K +-ATPase activity was also elevated. Pseudobranch Na +, K +-ATPase activity did not increase 10 days after transfer from fresh water to 34 ppt seawater, a treatment that resulted in a twofold increase in gill Na +, K +-ATPase activity. Cortisol (50 μg/g) and ovine growth hormone (5 μg/g) implants had no effect on pseudobranch Na +, K +-ATPase activity in underyearling chinook salmon, while gill Na +, K +-ATPase activity was stimulated by each hormone. In yearling chinook salmon, only cortisol stimulated pseudobranch Na +, K +-ATPase activity 14 days post-implantation. It was concluded that the pseudobranch differs from the gill in terms of the regulation of Na +, K +-ATPase activity and a role during adaptation to seawater is likely to be limited.

Myxobolus absonus sp. n. (Myxozoa: Myxosporea) parasitizing pimelodus maculatus (siluriformes: Pimelodidae), a South American freshwater fish.

A new myxoporean species is described from a freshwater fish in Brazil. Myxobolus absonus sp. n. was found infecting Pimelodus maculatus captured in the river Piracicaba, State of São Paulo, Brazil. Cysts were found free in the opercular cavity. The spores are large (length--15.7 +/- 1.5 microns, width--10.2 +/- 0.7 microns; mean +/- S.D.) and oval in shape, with the anterior end slightly pointed. The spore valves are relatively thin, smooth, and asymmetrical in a frontal view. The polar capsules are pyriform in shape, and unequal in size; the largest are 6.4 +/- 0.7 microns long and 3.6 +/- 0.5 microns wide, while the smallest are 4.2 +/- 0.6 microns long and 2.5 +/- 0.5 microns wide.

Aquatic prey capture in ray-finned fishes: a century of progress and new directions.

The head of ray-finned fishes is structurally complex and is composed of numerous bony, muscular, and ligamentous elements capable of intricate movement. Nearly two centuries of research have been devoted to understanding the function of this cranial musculoskeletal system during prey capture in the dense and viscous aquatic medium. Most fishes generate some amount of inertial suction to capture prey in water. In this overview we trace the history of functional morphological analyses of suction feeding in ray-finned fishes, with a particular focus on the mechanisms by which suction is generated, and present new data using a novel flow imaging technique that enables quantification of the water flow field into the mouth. We begin with a brief overview of studies of cranial anatomy and then summarize progress on understanding function as new information was brought to light by the application of various forms of technology, including high-speed cinematography and video, pressure, impedance, and bone strain measurement. We also provide data from a new technique, digital particle image velocimetry (DPIV) that allows us to quantify patterns of flow into the mouth. We believe that there are three general areas in which future progress needs to occur. First, quantitative three-dimensional studies of buccal and opercular cavity dimensions during prey capture are needed; sonomicrometry and endoscopy are techniques likely to yield these data. Second, a thorough quantitative analysis of the flow field into the mouth during prey capture is necessary to understand the effect of head movement on water in the vicinity of the prey; three-dimensional DPIV analyses will help to provide these data. Third, a more precise understanding of the fitness effects of structural and functional variables in the head coupled with rigorous statistical analyses will allow us to better understand the evolutionary consequences of intra- and interspecific variation in cranial morphology and function.

Surface ultrastructure of the gills of the mullets Mugil curema, M. liza and M. platanus (Mugilidae, Pisces).

Mugil curema, M. liza, and M. platanus were collected from the southeastern and southern coast of Brazil. The second gill arches were analyzed by scanning electron microscopy and histology. The highest density of chloride and mucus-secreting cells was observed in the gill filaments of M. liza and M. platanus. Spines are scarce and were found only in the pharyngeal region of M. curema. The dorsal angle of curvature of the simple projections is most reduced in the rakers of M. liza and M. platanus. The raker borderline on the internal side of the arches of M. curema has grooves that do not occur in the other two species. On the external side of the branchial arches, the borders of the rakers of M. liza and M. platanus are smooth. The shape of the rakers is characteristic for each species: in M. curema, it resembles the letter "D"; in M. liza, it is trapezoidal, and in M. platanus, it is triangular. Thus there is a morphologic similarity between M. liza and M. platanus, and both differ from M. curema. All three species show elongated and extremely elaborated rakers that are placed next to each other and turned toward the opercular cavity. There are few taste buds and only several mucus-secreting cells along the whole pharyngeal region. These characteristics suggest that these species do not select food chemically but obtain it mechanically with the rakers and aggregate it with mucus.