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Achromatic (luminance) vision is used by animals to perceive motion, pattern, space and texture. Luminance contrast sensitivity thresholds are often poorly characterised for individual species and are applied across a diverse range of perceptual contexts using over-simplified assumptions of an animal’s visual system. Such thresholds are often estimated using the Receptor Noise Limited model (RNL) using quantum catch values and estimated noise levels of photoreceptors. However, the suitability of the RNL model to describe luminance contrast perception remains poorly tested.Here, we investigated context-dependent luminance discrimination using triggerfish (Rhinecanthus aculeatus)presented with large achromatic stimuli (spots) against uniform achromatic backgrounds of varying absolute and relative contrasts. ‘Dark’ and ‘bright’ spots were presented against relatively dark and bright backgrounds. We found significant differences in luminance discrimination thresholds across treatments. When measured using Michelson contrast, thresholds for bright spots on a bright background were significantly higher than for other scenarios, and the lowest threshold was found when dark spots were presented on dark backgrounds. Thresholds expressed in Weber contrast revealed increased contrast sensitivity for stimuli darker than their backgrounds, which is consistent with the literature. The RNL model was unable to estimate threshold scaling across scenarios as predicted by the Weber-Fechner law, highlighting limitations in the current use of the RNL model to quantify luminance contrast perception. Our study confirms that luminance contrast discrimination thresholds are context-dependent and should therefore be interpreted with caution.

Achromatic (luminance) vision is used by animals to perceive motion, pattern, space and texture. Luminance contrast sensitivity thresholds are often poorly characterised for individual species and are applied across a diverse range of perceptual contexts using over-simplified assumptions of an animal's visual system. Such thresholds are often estimated using the Receptor Noise Limited model (RNL) using quantum catch values and estimated noise levels of photoreceptors. However, the suitability of the RNL model to describe luminance contrast perception remains poorly tested. Here, we investigated context-dependent luminance discrimination using triggerfish (Rhinecanthus aculeatus) presented with large achromatic stimuli (spots) against uniform achromatic backgrounds of varying absolute and relative contrasts. ‘Dark’ and ‘bright’ spots were presented against relatively dark and bright backgrounds. We found significant differences in luminance discrimination thresholds across treatments. When measured using Michelson contrast, thresholds for bright spots on a bright background were significantly higher than for other scenarios, and the lowest threshold was found when dark spots were presented on dark backgrounds. Thresholds expressed in Weber contrast revealed increased contrast sensitivity for stimuli darker than their backgrounds, which is consistent with the literature. The RNL model was unable to estimate threshold scaling across scenarios as predicted by the Weber-Fechner law, highlighting limitations in the current use of the RNL model to quantify luminance contrast perception. Our study confirms that luminance contrast discrimination thresholds are context-dependent and should therefore be interpreted with caution.

Despite high rates of photosynthetic oxygen production during the day, the warm waters of coral reefs are susceptible to hypoxia at night due to elevated respiration rates at higher temperatures that also reduce the solubility of oxygen. Hypoxia may be a challenge for coral-reef fish that hide in the reef to avoid predators at night. Triggerfishes (Balistidae) are found in a variety of reef habitats, but they also are known to find refuge in reef crevices and holes at night, which may expose them to hypoxic conditions. The critical oxygen tension (P crit) was determined as the point below which oxygen uptake could not be maintained to support standard metabolic rate (SMR) for five species of triggerfish. The triggerfishes exhibited similar levels of hypoxia tolerance as other coral-reef and coastal marine fishes that encounter low oxygen levels in their environment. Two species, Rhinecanthus rectangulus and R. aculeatus, had the lowest P crit (~ 3.0 kPa O2), comparable to the most hypoxia-tolerant obligate coral-dwelling gobies, while Odonus niger and Sufflamen bursa were moderately tolerant to hypoxia (P crit ~ 4.5 kPa), and Xanthichthys auromarginatus was intermediate (P crit ~ 3.7 kPa). These differences in P crit were not due to differences in oxygen demand, as all the species had a similar SMR once mass differences were taken into account. The results suggest that triggerfish species are adapted for different levels of hypoxia exposure during nocturnal sheltering within the reef.

Terrestrial animals compute shortcuts through their environment by integrating self-motion vectors containing distance and direction information. The sensory and neural mechanisms underlying this navigational feat have been extensively documented, but their evolutionary origins remain unexplored. Among extant vertebrates, the teleost fish make up one of the most diverse and earliest-branching phylogenetic groups, and provide a powerful system to study the origins of vertebrate spatial processing. However, how freely-swimming teleost fish collect and compute metric spatial information underwater are unknown. Using the Picasso triggerfish,Rhinecanthus aculeatus, we investigate the functional and mechanistic basis of distance estimation in teleost fish for the first time. We show that a fish can learn and remember distance travelled with remarkable accuracy. By analysing swimming trajectories, we form hypotheses about how distance is represented in the teleost brain, and propose that distance may be encoded by dedicated neural structures in a similar way to terrestrial vertebrates. Finally, we begin exploring the sensory mechanisms underlying distance estimation in fish. Many walking animals use a step counter for odometry. By quantifying finbeat use during our distance task, we show that a functionally equivalent finbeat counter is unlikely to provide reliable and precise distance information in an aquatic environment.

Rhinecanthus verrucosus (Linnaeus 1758) —Blackpatch triggerfish (Fig. 164) Status at New Ireland. First recorded from Port Praslin, New Ireland as Balistes praslinoides by Lesson (1831: 117, poissons pl. 9, fig. 3), based on MNHN B.1771; reported as Balistes verrucosus by Günther (1910: 445), and from St. Mathias by Duncker & Mohr (1929: 74). Specimens observed in Kavieng Lagoon by Jeff Kinch during ACIAR Aquarium Survey in 2013 (see Teitelbaum et al. 2013: 15, R. verucosus); a specimen photographed at Lissenung Island, Kavieng District, 1 m depth, by Dean Tully on 27 June 2014; a video of a specimen taken in Senta Passage, east of New Hanover, at 5–16 m depth, St. KR118, in 2014 (identified by Barry C. Russell). ZMH material. Distribution and habitat. New Ireland: 1, 2, 3, 4.—General distribution: Seychelles and Chagos Archipelago east to western Caroline Islands and Vanuatu, north to southern Japan, south to northern Australia and New Caledonia. Found in sheltered areas of mixed coral and rubble, or in seagrass habitats, 1–20 m depth. Marine., Published as part of Andréfouët, Serge, Chen, Wei-Jen, Kinch, Jeff, Mana, Ralph, Russell, Barry C., Tully, Dean & White, William T., 2019, Checklist of the marine and estuarine fishes of New Ireland Province, Papua New Guinea, western Pacific Ocean, with 810 new records, pp. 1-360 in Zootaxa 4588 (1) on page 324, DOI: 10.11646/zootaxa.4588.1.1, http://zenodo.org/record/2988163, {"references":["Lesson, R. P. (1831) Poissons. In: Duperrey, L. I. (ed.), Foyage autour du monde, ..., sur la corvette de La Majeste La Coquille, pendant les annees 1822, 1823, 1824 et 1825..., Zoologie tome 2. Paris. (Pt. 1, text): 66 - 238; Atlas (1832): pls. 1 - 38.","Gunther, A. C. L. G. (1910) Andrew Garrett's Fische der Sudsee. Band III, Heft IX. Journal des Museum Godeffroy, Hamburg, 6 (17), i-vi + 389 - 515, pls. 161 - 180.","Duncker, G. & Mohr, E. (1929) Die Fische der Sudsee-Expedition der Hamburgischen Wissenschaftlichen Stiftung 1908 - 1909. 3. Teil. Mitteilungen aus dem Zoologischen Staatsinstitut und Zoologischen Museum in Hamburg, 44, 57 - 84.","Teitelbaum, A., Nahacky, A. & Kinch, J. (2013) A commercial survey of aquarium fish species in the Kavieng Lagoon, New Ireland Province, Papua New Guinea. Report, James Cook University, Townsville, 1 - 21."]}

Rhinecanthus aculeatus (Linnaeus 1758) —Blackpatch triggerfish Status at New Ireland. First recorded from Carteret Harbour, New Ireland as Balistes aculeatus by Peters (1877: 852). A specimen photographed at Lissenung Island, Kavieng District by Dietmar Amon on 20 Feb. 2010. Distribution and habitat. New Ireland: 2, 3.—General distribution: Eastern Atlantic: Senegal, South Africa; Indo-West Pacific: East and South Africa, Mozambique Channel, Seychelles, Madagascar and Mascarenes east to Pitcairn Group, north to southern Japan and Ogasawara Islands, south to Australia and Lord Howe Island. Found on reef flats or in coral reef lagoons, 0–50 m depth. Marine., Published as part of Andréfouët, Serge, Chen, Wei-Jen, Kinch, Jeff, Mana, Ralph, Russell, Barry C., Tully, Dean & White, William T., 2019, Checklist of the marine and estuarine fishes of New Ireland Province, Papua New Guinea, western Pacific Ocean, with 810 new records, pp. 1-360 in Zootaxa 4588 (1) on pages 323-324, DOI: 10.11646/zootaxa.4588.1.1, http://zenodo.org/record/2988163, {"references":["Peters, W. C. H. (1877) Ubersicht der wahrend der von 1874 bis 1876 unter der Commando des Hrn. Capitan z. S. Freiherrn von Schleinitz ausgefuhrten Reise S. M. S. Gazelle gesammelten und von der Kaiserlichen Admiralitat der Koniglichen Akademie der Wissenschaften ubersandten Fische. Monatsberichte der Koniglichen Preuss [ischen] Akademie der Wissenschaften zu Berlin, 1876, 831 - 854."]}

Rhinecanthus rectangulus (Bloch & Schneider [ex Lacepède & Commerson] 1801)—Wedgetail triggerfish Status at New Ireland. New record, based on a video of a specimen taken at Kavieng, Kavieng District, 0–11 m depth, St. KR22, 5 June 2014 (identified by Barry C. Russell). Distribution and habitat. New Ireland: 2.—General distribution: Red Sea, East Africa, Seychelles, Madagascar and Mascarenes east to Pitcairn Group, north to southern Japan and Ogasawara Islands, south to Lord Howe Island and Kermadec Islands, and Hawaiian Islands. Found on reef flats or in seaward coral reefs, 1–12 m depth. Marine., Published as part of Andréfouët, Serge, Chen, Wei-Jen, Kinch, Jeff, Mana, Ralph, Russell, Barry C., Tully, Dean & White, William T., 2019, Checklist of the marine and estuarine fishes of New Ireland Province, Papua New Guinea, western Pacific Ocean, with 810 new records, pp. 1-360 in Zootaxa 4588 (1) on page 324, DOI: 10.11646/zootaxa.4588.1.1, http://zenodo.org/record/2988163

Miyazaki, Y.; Murase, A.; Shiina, M.; Masui, R., and Senou, H., 2015. Integrating and utilizing citizen biodiversity data on the Web for science: An example of a rare triggerfish hybrid image provided by a sport fisherman. We report a photograph of the rare triggerfish hybrid, Rhinecanthus aculeatus × R. rectangulus (order Tetraodontiformes; family Balistidae), from Miyako-jima Island, Ryukyu Islands, southern Japan, that was provided by a sport fisherman via WEB sakana-zukan (an online photographic database of fish in Japan). The image was registered in the Fish Image Database of the Kanagawa Prefectural Museum of Natural History to make it available for scientific scrutiny. Here we emphasize the importance of communication between citizens, such as fishermen, scuba divers, and others, and experts via the Internet, to make possible the processing of biodiversity information provided by citizens into museum collections. This communication contributes Global Biodiversity Information Facility data ...

The ability to produce sounds for acoustic communication is known in different Balistidae species but the eventual synapomorphic aspect of the mechanism remains to be shown. In Rhinecanthus aculeatus, sounds result from alternate sweeping movements of the right and left pectoral fins, which push a system of three scutes against the swim bladder wall. In this study, we made a comparison between the sounds produced by this species and two additional ones (Balistapus undulatus and Rhinecanthus rectangulus) using hand-held specimens to provide a description of the sound mechanism. The results highlighted that the sound production mechanism is similar in the three species. According to recent phylogenetic data and shared morphological features, this mechanism could be common to the majority of Balistidae family members and all species could be capable of sound production using pectoral fins.

Humans group components of visual patterns according to their colour, and perceive colours separately from shape. This property of human visual perception is the basis behind the Ishihara test for colour deficiency, where an observer is asked to detect a pattern made up of dots of similar colour with variable lightness against a background of dots made from different colour(s) and lightness. To find out if fish use colour for object segregation in a similar manner to humans, we used stimuli inspired by the Ishihara test. Triggerfish (Rhinecanthus aculeatus) were trained to detect a cross constructed from similarly coloured dots against various backgrounds. Fish detected this cross even when it was camouflaged using either achromatic or chromatic noise, but fish relied more on chromatic cues for shape segregation. It remains unknown whether fish may switch to rely primarily on achromatic cues in scenarios where target objects have higher achromatic contrast and lower chromatic contrast. Fish were also able to generalize between stimuli of different colours, suggesting that colour and shape are processed by fish independently.

The reproduction of Rhinecanthus aculeatus (Linnaeus, 1758), a tropical Indo-Pacific reef fish, occurs around the full and new moon (Kuwamura 1997). Spawning begins 16 to 45 min before the sunrise. The courtships begin 7 to 27 min before the spawning. A specific behaviour of the courtships is when the male places its rostrum against the caudal peduncle of the female (Kuwamura 1997). Observations have been recorded in the lagoon of Tiahura [shallow sandy area (0.5 - 2 m deep) with algae Hypnea spinella (C.Agardh) Kutzing, 1847 - Moorea, French Polynesia; 17°29′27′ S, 149°53′32″O] in March and April 2015. Fifteen R. aculeatus (five males and ten females) lived in this area where the males have territories, which included the subterritories of the females. During video-recorded courtships, in addition to the behaviour described by Kuwamura (the nuzzling), two new behaviours have been observed: circling and touching. During the circling, the male and the female swim to the surface in progressively larger circles (Fig. 1). The circling behaviour has been observed in other Balistidae such as Pseudobalistes flavimarginatus (Ruppell, 1829) and Balistapus undulatus (Park, 1797) (Lobel and Johannes 1980). During the touching, the abdomens of the male and the female’s touch each other without gametes emission (Fig. 2). The touching has been reported for Xanthichthys mento (Jordan and Gilbert 1882) (Kawase 2003). Although Balistidae present different reproductive strategies, they have common reproduction features, such as the time and the day of hatching and spawning (Kawase 2003). Our observations are innovative because the courtship of R. aculeatus is more complicated than previously described. This result suggests, thus, that Balistidae have also some common courtship behaviour features. These behaviours may facilitate the release of gametes, as with the nuzzling (Kuwamura 1997) or can convince the partner to mate. We do not know if these patterns are phylogenetically related. But as the egg care strategy of Balistidae (biparental vs maternal) appears to be related to the distribution of food and breeding sites, more than by the phylogeny (Kuwamura 1997), more studies on this topic will be useful to better understand the establishement of these behaviours.

The ability to produce sound has been known for decades in Balistidae. Sounds of many species have been recorded and a variety of sound-producing mechanisms have been proposed, including teeth stridulation, collision of the buccal teeth and movements of the fins. The best-supported hypothesis involves movements of the pectoral fin against the lateral part of the swimbladder, called a drumming membrane. In this study, we describe for the first time the sounds made by the blackbar triggerfish Rhinecanthus aculeatus, which are like short drum rolls with an average duration of 85 ms, 193 Hz dominant frequency and 136 dB SPL level at 3 cm distance. The sounds are a series of pulses that result from alternate sweeping movements of the right and left pectoral fins, which push a system of three scutes that are forced against the swimbladder wall. Pulses from each fin occur in consecutive pairs. High-speed videos indicate that each pulse consists of two cycles. The first part of each cycle corresponds to the inward buckling of the scutes, whereas the second part of the cycle corresponds to an apparent passive recoil of the scutes and swimbladder wall. This novel sound production mechanism is probably found in many members of Balistidae because these peculiar scutes occur in other species in the family. Comparison of sound characteristics from fishes of different sizes shows that dominant frequency decreases with size in juveniles but not in adults.

Coral reef fish present the human observer with an array of bold and contrasting patterns; however, the ability of such fish to perceive these patterns is largely unexamined. To understand this, the visual acuity of these animals - the degree to which they can resolve fine detail - must be ascertained. Behavioural studies are few in number and anatomical analysis has largely focused on estimates of ganglion cell density to predict the visual acuity in coral reef fish. Here, we report visual acuity measures for the triggerfish Rhinecanthus aculeatus. Acuity was first assessed using a series of behavioural paradigms and the figures were then contrasted with those obtained anatomically, based on photoreceptor and ganglion cell counts. Behavioural testing indicated an upper behavioural acuity of 1.75 cycles·degree-1, which is approximately the same level of acuity as that of the goldfish (Carassiusauratus). Anatomical estimates were then calculated from wholemount analysis of the photoreceptor layer and Nissl staining of cells within the ganglion cell layer. Both of these anatomical measures gave estimates that were substantially larger (7.75 and 3.4 cycles·degree-1 for the photoreceptor cells and ganglion cells, respectively) than the level of acuity indicated by the behavioural tests. This indicates that in this teleost species spatial resolution is poor compared to humans (30-70 cycles·degree-1) and it is also not well indicated by anatomical estimates.

Coral reef fishes are among the most colourful animals in the world. Given the diversity of lifestyles and habitats on the reef, it is probable that in many instances coloration is a compromise between crypsis and communication. However, human observation of this coloration is biased by our primate visual system. Most animals have visual systems that are ‘tuned’ differently to humans; optimized for different parts of the visible spectrum. To understand reef fish colours, we need to reconstruct the appearance of colourful patterns and backgrounds as they are seen through the eyes of fish. Here, the coral reef associated triggerfish, Rhinecanthus aculeatus , was tested behaviourally to determine the limits of its colour vision. This is the first demonstration of behavioural colour discrimination thresholds in a coral reef species and is a critical step in our understanding of communication and speciation in this vibrant colourful habitat. Fish were trained to discriminate between a reward colour stimulus and series of non-reward colour stimuli and the discrimination thresholds were found to correspond well with predictions based on the receptor noise limited visual model and anatomy of the eye. Colour discrimination abilities of both reef fish and a variety of animals can therefore now be predicted using the parameters described here.

The prevalence of a haremic mating system type with parental care is one of the main characteristics of the modern triggerfish family (Balistidae). In addition, intraspecific modifications of the mating system in relation to environmental conditions have been recognized. Thirteen months of observation of mating units in a natural population of Rhinecanthus aculeatus from Okinawa Island, Japan, revealed that the mating system in this species involved a mixture of polygyny, monogamy, and potential promiscuity in solitary females. Females defended individual, multi-purpose territories, while males engaged in female defence (“female defence polygyny”) using displays and overt aggressions that advertised that territories were occupied. Male size was strongly linked to access to multiple females (i.e. polygyny). Plasticity in the mating system was related to male–male competition and the ability of females to reject males. An increase in the proportion of monogamous pair territories over the course of the reproductive season was positively correlated with the adult sex ratio (increased male density relative to females), and facultative monogamy was enhanced under a less female-biased sex ratio. A comparison between female and male mating success (number of matings) and the adjustment of the mating status over time revealed that polygyny was advantageous and the optimal mating system for males. Females achieved higher number of matings when pairing with larger males, but mating success was not negatively affected by the actual mating status, and females did not attempt to escape polygyny. Polygyny is therefore considered as the primary mating system in R. aculeatus.

To understand age and growth of the Picasso triggerfish, Rhinecanthus aculeatus, monthly sampling was conducted from February 2010 to October 2011 on the subtropical Okinawa Island, Japan, using trammel net and speargun. Fish were measured by weight (W) and standard length (SL) and age was determined by examining thin-sections of the first dorsal spine and the second abdominal vertebra. A total of 352 fish were caught ranging from 20.9 mm to 209.5 mm (SL). Marginal increment analysis indicated that translucent rings were deposited annually during the colder season from October to January. The relationship of observed SL and age was described by the original form of the von Bertalanffy growth equation. Male and female growth models were significantly different. Overall growth was rapid during the first 2.5 years for both sexes, thereafter growth curves diverged. Males consequently reached larger sizes and greater ages. Maximum age for males and females was 13.5 and 9.5 years, respectively. Regression models of somatic growth (SL) as a function of vertebral and spine radii were significantly correlated (r = 0.98 and r = 0.96, respectively). According to the weight–length relationship, growth in R. aculeatus was negative allometric. Small recruits (SL

Paternal care is predominant among telcost fishes with external fertilization. This study describes maternal care in a haremic coral-reef fish and discusses the possible factors leading to its evolution. Both sexes of the triggerfish Rhinecanthus aculeatus (Balistidae) maintained territories; some individuals for more than 8 years. Each male's territory overlapped 2-3 female territories. Pair-spawning occurred around sunrise. Only females cared for the demersal eggs until hatching, which occurred just after sunset on the day of the spawning. No predation was observed on eggs under the maternal care, but experimental removal of parental females decreased the hatching rate to nearly zero. Egg-guarding females foraged as frequently as males, but less than half of non-spawning days. Spawning occurred only in the periods of about 1 wk around the new or full moon, and individual females spawned up to three times in each period. Thus, the maternal care did not significantly affect the duration of the females' spawning intervals, while males would suffer mate loss if they performed parental care. In this situation, maternal care should be the evolutionarily stable strategy. Evolutionary transition from no care to maternal care and then to biparental care is suggested in the Balistidae.

International audience; Cableia balistidicola n. sp. is described from Abalistes stellatus (type-host) off New Caledonia (type-locality) and the Great Barrier Reef and Pseudobalistes fuscus off New Caledonia and Rhinecanthus aculeatus off Moorea, French Polynesia. It is distinguish able by its large ventral sucker with a highly developed sphincter around the aperture. Cableia pudica is reported from Meuschenia freycineti off northern Tasmania, M. hippocrepis off south-western Western Australia and northern Tasmania and Acanthaluteres spilomelanurus off Kangaroo island, South Australia. Measurements of C. pudica are given and the distinguishing features of the three known species of Cableia are discussed and summarised in a key. C. balistidicola is reported only in balistid fishes in the tropical Pacific Ocean and C. pudica is reported only in monacanthid fishes in Australian coastal waters.

There was an error published in J. Exp. Biol. 220 , [186-193][1]. The surname of Sam Van Wassenbergh was incorrectly displayed. This has been corrected in the online full-text and PDF versions. The authors apologise for any inconvenience this may have caused. [1]: /lookup/volpage/220/186?iss=2

Double cones (DCs) are the most common cone types in fish, reptiles and birds. It has been suggested that DCs are used for achromatic tasks such as luminance, motion and polarization vision. Here we show that a reef fishRhinecanthus aculeatuscan discriminate colours on the basis of the difference between the signals of individual members of DCs. This is the first direct evidence that individual members of DCs are used in colour vision as independent spectral channels.

Summary Animals use coloured signals for a variety of communication purposes, including to attract potential mates, recognize individuals, defend territories and warn predators of secondary defences (aposematism). To understand the mechanisms that drive the evolution and design of such visual signals, it is important to understand the visual systems and potential response biases of signal receivers. Here, we provide raw data on the spectral capabilities of a coral reef fish, Picasso triggerfish Rhinecanthus aculeatus, which are potentially trichromatic with three cone sensitivities of 413 nm (single cone), 480 nm (double cone, medium sensitivity), 528 nm (double cone, long sensitivity) and a rod sensitivity of 498 nm. The ocular media have a 50% transmission cut off at 405 nm. Behavioural experiments confirmed colour vision over their spectral range; triggerfish were significantly more likely to choose coloured stimuli over grey distractors, irrespective of luminance. We then examined whether response biases existed towards coloured and patterned stimuli to provide insights into how visual signals - in particular, aposematic colouration - may evolve. Triggerfish showed a preferential foraging response bias to red and green stimuli, in contrast to blue and yellow, irrespective of pattern. There was no response bias to patterned over monochromatic non-patterned stimuli. A foraging response bias towards red in fish differs to that of avian predators, who often avoid red food items. Red is frequently associated with warning colouration in terrestrial environments (ladybirds, snakes, frogs), whilst blue is used in aquatic environments (blue-ringed octopus, nudibranchs); whether the design of warning (aposematic) displays is a cause or consequence of response biases is unclear.

Investigations to determine whether juvenile gnathiid isopods are vectors of haemogregarines between coral reef fishes were undertaken at Lizard Island, Australia. Haemogregarina balistapi parasitaemias in triggerfish, Rhinecanthus aculeatus, decreased under gnathiid-free, laboratory conditions, compared with those in tagged R. aculeatus returned to the reef. Gnathia aureamaculosa juveniles were common ectoparasites of reef R. aculeatus and laboratory reared specimens of this gnathiid were fed on R. aculeatus infected with H. balistapi. Subsequent squashes of this gnathiid contained haemogregarine gamonts similar to those seen in blood films of R. aculeatus, and haemogregarine developmental stages, including oocysts, sporozoites, meronts and merozoites. Biological transmission of H. balistapi and a second haemogregarine species, Haemogregarina bigemina, using laboratory reared gnathiids to several species of triggerfishes and surgeonfishes raised from larvae was then attempted. Investigations involved recipient fish ingesting, or being bitten by, G. aureamaculosa juveniles fed on donor fish with haemogregarines; control fish were exposed to gnathiids fed on uninfected donor fish. Subsequently, no haemogregarines were detected in recipient triggerfishes and controls were negative. However, a recipient surgeonfish, Acanthurus xanthopterus, which had ingested gnathiids likely infected with donor fish H. balistapi, carried H. bigemina-like stages. A second recipient surgeonfish, which had ingested gnathiids presumed to be infected with H. bigemina, also carried haemogregarine stages. Finally, a third surgeonfish apparently carried haemogregarines after gnathiids presumed to be infected with H. bigemina had bitten this fish, although not all gnathiids were recovered during the trials and the third infected surgeonfish may have also ingested gnathiids. The study provides strong evidence that G. aureamaculosa is the definitive host of H. balistapi, to our knowledge the first such observation from a coral reef environment. Although transmission of H. balistapi has not yet been demonstrated, laboratory trials tend to support the view that G. aureamaculosa is also a potential vector of H. bigemina between surgeonfish.

Suspected viral erythrocytic necrosis (VEN) was detected in blood films from an immature blackbar triggerfish, Rhinecanthus aculeatus, captured on a patch reef at Lizard Island, Great Barrier Reef in November 2005, probably the first record of such an infection from Australia. The fish was kept in captivity and sampled intermittently until December 2007. Giemsa-stained blood films showed initially ~18% of mature erythrocytes affected by the VEN-like condition, but accompanying erythroblasts appeared free from infection. Erythrocytes with VEN-like bodies were smooth or crenated in outline, while the inclusion bodies were intracytoplasmic, single or paired, round in outline, stained deep magenta and were between 0.5–1.7 μm across. Bodies associated with clouds of granular material, fine eosinophilic haloes, and distinct pink-stained comet-tails, were also observed. The DNA content of the VEN-like bodies was confirmed by their green fluorescence following acridine orange staining. Infection levels in this fish fell to 0.4% of mature erythrocytes by May 2006 and persisted at this level until December 2007, when the fish died after just over two years in captivity. Squashes of haematophagous, juvenile gnathiid isopods taken from this fish on initial capture, also contained eosinophilic VEN-like bodies within digesting erythrocytes, suggesting that these crustaceans may be vectors of the condition observed.

Due to oceanic exploitation necessities, such as benthonic archaeology, exploration to benthonic mineral resources and salvaging of sunken ships, a novel kind of fish-like robot has become one of the hot topics in the field of underwater vehicles. For such aquatic robots, high maneuverability and great stability are more important than high speed or remarkable accelerating performance. This paper extracts some interesting and helpful inspirations from Rhinecanthus aculeatus, which belongs to MPF (median and/or paired fin) propulsion fish and impresses researchers with agility by cooperative undulations of the dorsal-and-anal fins. To begin with, a selected specimen of R. aculeatus was filmed in a large aquarium (150 cm times 50 cm times 60 cm) in which artificial seawater was maintained at 26 degC or so, for observations and measurements. Then, several characteristics in morphology and locomotion were respectively analyzed with image processing and other approaches based on the filmed swimming sequences. Finally, we sum up some bionic inspirations of R. aculeatus for a novel robfish which is distinct with an undulatory multi-fin biopropulsor, and this conceptual aquatic vehicle has been expected to exhibit better maneuverability, greater stability, and higher efficiency

This paper proposes a novel conceptual underwater bio-robot inspired by Rhinecanthus aculeatus, which belongs to median and/or paired fin (MPF) propulsion fish and impresses researchers with agility by cooperative undulation of the dorsal-and-anal fins. Such a fish-like robot is anticipated to outperform the conventional aquatic robots in maneuverability and stability for oceanic exploitation necessities, e.g. benthonic mineral exploration. To begin with, a specimen of R. aculeatus was filmed in a glass aquarium (150cm times 50cm times 60cm) in which artificial seawater was maintained at 26 degC or so. Afterwards, we analyzed a few characteristics in morphology and locomotion with image processing and other approaches. The morphological and kinematical bionic inspirations were summarized, and in succession, we elaborately delineated the design scheme of our conceptual robotic fish including the schematic architectures, the structural and outside form, and the undulatory multi-fin propulsor

The effect of tetrodotoxin (TTX) was examined on action potentials in various fishes obtained in the waters of the Great Barrier Reef. The action potentials in muscles of all pufferfishes examined (seven species) were found to be insensitive to 3 × 10−6 M TTX. On the other hand, TTX blocked the action potentials in common hardy-head (Pranesus ogilbyi), slender remora (Echeneis naucrates) and parrotfish (Callyodon pyrrhostethus) at a concentration of 3 × 10−7 M. The dose-response curve fits well the curve predicted by the Langmuir adsorption isotherm. The dissociation constants thus determined in the above mentioned fishes were 3 × 10−8 M, 6 × 10−8 M and 5 × 10−8 M respectively. In contrast to the small dissociation constants found in ordinary fishes, some fishes closely related to pufferfishes have large dissociation constants. They are 3 × 10−7 M in porcupinefish (Diodon holacanthus), 1 × 10−7 M in boxfish (Rhynchostracion nasus) and 5 × 10−7 M in triggerfish (Rhinecanthus aculeatus). We speculate that the resistivity of pufferfish action potentials to TTX is a result of evolutionary change and that the selection may have been done by TTX itself. The effect of saxitoxin (STX) on pufferfish action potentials (Arothron hispidus) was examined and it was found that the action potentials are also resistant to 3 × 10−7 M STX whereas those of common hardy-head (Pranesus ogilbyi) muscle were blocked by 3 × 10−8M. Possible molecular mechanisms of the TTX resistivity are discussed.

In the course of a general investigation of the optic system in some trigger-fishes, a hypothalamic, ventricular channel-system with pores, leading to the outside of the brain, has been discovered in the inferior lobes of Rhinecanthus aculeatus (Balistidae). A description of the morphological relations of the channel-system to the blood-vessel-supply and the cranium suggests that the organ-systems involved form a functional unit. The possibility of a hormone-producing system is discussed in the light of physiological and ecological aspects.

SUMMARYTo determine the energetic costs of rigid-body, median or paired-fin (MPF)swimming versus undulatory, body-caudal fin (BCF) swimming, we measured oxygen consumption as a function of swimming speed in two MPF swimming specialists, Schlegel's parrotfish and Picasso triggerfish. The parrotfish swam exclusively with the pectoral fins at prolonged swimming speeds up to 3.2 total lengths per second (L s-1; 30 min critical swimming speed, Ucrit). At higher speeds, gait transferred to a burst-and-coast BCF swimming mode that resulted in rapid fatigue. The triggerfish swam using undulations of the soft dorsal and anal fins up to 1.5 L s-1, beyond which BCF undulations were recruited intermittently. BCF swimming was used continuously above 3.5 L s-1, and was accompanied by synchronous undulations of the dorsal and anal fins. The triggerfish were capable of high, prolonged swimming speeds of up to 4.1 L s-1 (30 min Ucrit). In both species, the rates of increase in oxygen consumption with swimming speed were higher during BCF swimming than during rigid-body MPF swimming. Our results indicate that, for these species,undulatory swimming is energetically more costly than rigid-body swimming, and therefore support the hypothesis that MPF swimming is more efficient. In addition, use of the BCF gait at higher swimming speed increased the cost of transport in both species beyond that predicted for MPF swimming at the same speeds. This suggests that, unlike for terrestrial locomotion, gait transition in fishes does not occur to reduce energetic costs, but to increase recruitable muscle mass and propulsive surfaces. The appropriate use of the power and exponential functions to model swimming energetics is also discussed.

Eleven new species of the genus Hatschekia Poche, 1902 (Copepoda: Siphonostomatoida: Hatschekiidae) are described based on female specimens from triggerfishes (Tetraodontiformes: Balistidae) caught in coastal waters of the Ryukyu Islands, Japan. These include Hatschekia hemicyclium n. sp. on Rhinecanthus rectangulus (Bloch & Schneider), R. aculeatus (L.) and R. verrucosus (L.); H. jonesi n. sp. on Sufflamen bursa (Bloch & Schneider) and S. fraenatum (Latreille); H. kabatai n. sp. and H. izenaensis n. sp. on Xanthichthys lineopunctatus (Hollard); H. churaumi n. sp. on Pseudobalistes flavimarginatus (Ruppell); H. zanpa n. sp. and H. fukurubi n. sp. on Balistapus undulatus (Park); H. mongarah n. sp. on Balistoides conspicillum (Bloch & Schneider); H. nakamurai n. sp. on Melichthys vidua (Richardson); H. mihkagan n. sp. on Odonus niger (Ruppell); and H. pseudobalistesi n. sp. on Pseudobalistes fuscus (Bloch & Schneider). Ten of the 11 new species, with the exception of H. fukurubi n. sp., share the intercoxal sclerites of legs 1 and 2 armed with 4 processes. This character differs from 87 of the known 97 species in Hatschekia. Of the 20 species with this character, the 10 new species are separated from each other mainly by the following morphological characters: the number of setal elements in the leg armature, on the antennule and the caudal ramus, the presence of posterior lobes on the trunk, the segmentation and form of the abdomen, and the length ratios of certain body parts.