Independent and conjugate eye movements during optokinesis in teleost fish

In response to movements involving a large part of the visual field, the eyes of vertebrates typically show an optokinetic nystagmus, a response in which both eyes are tightly yoked. Using a comparative approach, this study sets out to establish whether fish with independent spontaneous eye movements show independent optokinetic nystagmus in each eye. Two fish with independent spontaneous eye movements, the pipefish Corythoichthyes intestinalis and the sandlance Limnichthyes fasciatus were compared with the butterflyfish Chaetodon rainfordi, which exhibits tightly yoked eye movements. In the butterflyfish a single whole-field stimulus elicits conjugate optokinesis, whereas the sandlance and pipefish show asynchronous optokinetic movements. In a split drum experiment, when both eyes were stimulated in opposite directions with different speeds, both the sandlance and the pipefish compensated independently with each eye. The optokinetic response in the butterflyfish showed some disconjugacy but was generally confused. When one eye was occluded, the seeing eye was capable of driving the occluded eye in both the butterflyfish and the pipefish but not in the sandlance. Monocular occlusion therefore unmasks a link between the two eyes in the pipefish, which is overridden when both eyes receive visual input. The sandlance never showed any correlation between the eyes during optokinesis in all stimulus conditions. This suggests that there are different levels of linkage between the two eyes in the oculomotor system of teleosts, depending on the visual input.

Molecular phylogenetics of Chaetodon and the Chaetodontidae (Teleostei : Perciformes) with reference to morphology

Butterflyfish are colourful, pan-tropical coastal fish that are important and distinctive members of coral reef communities. A successful systematic scheme and a robust phylogeny is considered essential in understanding further their biogeography and ecology, although recent cladistic treatments of butterflyfish phylogeny, based on soft tissue and bone morphology and coded at the generic and subgeneric levels, differ in character coding and subsequently tree topology. This study provides an independent test of the morphologically based hypotheses, using molecular systematic data from two partial mitochondrial gene fragments, cytochrome b (cytb) and small subunit rRNA (rrnS), for 52 ingroup chaetodontids and seven pomacanthids used to root the molecular trees. Individual gene trees were largely compatible and a combined molecular phylogeny, inferred from Bayesian analysis, was used to test alternative hypotheses suggested by morphological analyses. The tree was also used to map the latest morphological matrix in order to evaluate potential synapomorphies for various nodes defining butterflyfish interrelationships. A clade comprised of Chelmon and Coradion was sister group to other chaetodontids. Heniochus and Hemitaurichthys were each resolved as monophyletic groups, and as sister taxa Of the taxa sampled, Prognothodes was resolved as the sister genus to Chaeotodon. Of the ten Chaetodon subgenera sampled, all were monophyletic but their interrelationships differed significantly from that inferred from morphological characters. Lepidochaetodon was the most basal subgenus followed by Exornator and the remaining subgenera. Molecular data support the sister group relationship between Corallochaetodon and Citharoedus suggested by morphology, but major differences occur among the remaining more derived taxa. Chaetodon trifascialis and C. oligacanthus were resolved as sister taxa adding weight to the inclusion of the latter in C. Megaprotodon. Of those pairs of taxa known to hybridize and sampled with molecular data, all were closely related phylogenetically, except those hybrids known to occur in the Rabdophorus subgenus. Two base changes separated C. pelewensis from C. paucifasciatus which have been regarded previously as a single species. Cytb provided greater resolution than rrnS and will likely provide additional resolution with greater taxon sampling.

A new species of Aponurus looss, 1907 (Digenea : Lecithasteridae) in butterflyfishes (Perciformes : Chaetodontidae) from New Caledonia

Aponurus chelebesoi n. sp. is described from Chaetodon auriga, C. citrinellus, C. ephippium, C. flavirostris, C. lineolatus, C. melannotus, C. mertensii, C. pelewensis, C. lunulatus, C. vagabundus, Coradion altivelis, Forcipiger flavissimus, Heniochus acuminatus, H. chrysostomus and H. monoceros from the southern coast of New Caledonia. It is distinguished from most species in the genera Aponurus (synonym Brachadena) and Lecithophyllum by its claviform (as opposed to oval to subglobular) vitelline lobes. Three species, A. pyriformis, Lecithophyllum vogeae and Brachadena cheilonis, have similar claviform vitelline lobes, but differ from A. chelebesoi in their tandem testes and the distinct egg-size.

Identical digeneans in coral reef fishes from French Polynesia and the Great Barrier Reef (Australia) demonstrated by morphology and molecules

Three coral reef fish species, Zanclus cornutus, Chaetodon vagabundus and Naso lituratus, were collected in French Polynesia and on the Great Barrier Reef, Queensland. These fish species were each infected by one morphologically similar digenean species in both localities; Schistorchis Zancli Hanson, 1953 was found in Zanclus cornutus. Preptetos laguncula Bray and Cribb, 1996 in Naso lituratus and Neohypocreadium dorsoporum Machida and Uchida, 1987 in Chaetodon vagabundus. In addition, on the Great Barrier Reef P. laguncula was also found in Naso unicornis and N. dorsoporum in Chaetodon ephippium and Chaetodon flavirostris. Morphometric differences between the species from the two sites were only slight. Sequences from the second internal transcribed spacer of the ribosomal DNA of each worm revealed total homology or negligible divergence between samples from hosts caught in French Polynesia and on the Great Barrier Reef. These results show that across more than 6000 km these digeneans are similar in morphology and genotype. Some species of fishes and molluscs a-re considered to have distributions that encompass the entire tropical Indo-West Pacific. These findings suggest that at least some of their parasites have similarly broad distributions. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.

Ptychogyliauchen, a new genus of Gyliauchenidae (Platyhelminthes: Digenea) from siganid fishes of the Indo-West Pacific

We propose a new genus of the Gyliauchenidae Fukui, 1929 ( Digenea), Ptychogyliauchen, gen. nov., for four new species that infect Indo-West Pacific siganid fishes. Ptychogyliauchen, gen. nov. is a morphologically distinctive genus, diagnosed principally by the presence of a highly convoluted oesophagus, which generally exceeds the total body length of the worm, and by the unusual folded structure of the ejaculatory duct. Ptychogyliauchen thetidis, sp. nov. is designated as the type species, and is described from the intestine of Siganus punctatus (Siganidae) from Heron Island, Great Barrier Reef, Queensland, Australia. Ptychogyliauchen himinglaeva, sp. nov. is described from the intestine of Siganus corallinus ( Siganidae) from Lizard Island, Great Barrier Reef, Queensland, Australia. Ptychogyliauchen leucothea, sp. nov. is described from the intestine of S. argenteus, and further recorded from S. fuscescens, off Ningaloo, Western Australia, Australia. Ptychogyliauchen thistilbardi, sp. nov. is described from the intestine of S. doliatus from Noumea, New Caledonia, and is also found in S. argenteus, S. canaliculatus, S. corallinus and S. spinus from Noumea, New Caledonia, and Moorea, Tahiti, French Pacific. Ptychogyliauchen thistilbardi, sp. nov. also occurs in the intestine of Chaetodon citrinellus (Chaetodontidae) from Moorea. A key to species is provided. All species have been described following morphological examination using light microscopy, and specimens of P. thetidis, sp. nov., P. leucothea, sp. nov. and P. thistilbardi, sp. nov. have been characterised using molecular methods. Sequences were obtained for a combination of nuclear ribosomal (28S (D1-D3) and ITS2) and mitochondrial (ND1) genes. A phylogenetic analysis of sequenced specimens of Ptychogyliauchen, gen. nov. was conducted using species of Petalocotyle Ozaki, 1934 for outgroup comparison. This analysis, based on alignments of the ITS2 and 28S (D1-D3) rDNA genes, supports monophyly of the geographically widespread P. thistilbardi, sp. nov., which is known from both siganid and chaetodontid hosts. We discuss the taxonomy of the genus and the host associations of each species and the group.

Does client size affect cleaner fish choice of client? An empirical test using client fish models

To determine whether the choice of client fishes in the cleaner fish Labroides dimidiatus was influenced by client size, cleaner fish were given a choice of equal amount of food spread on large and small client redfin butterflyfish Chaetodon trifasciatus models. All large models received bites from cleaners compared to 27% for small models. Seventy-nine per cent of cleaners took their first bite from the large fish model. The results suggest that client size may affect cleaner fish choice.

Cardicola Short, 1953 and Braya n. gen. (Digenea : Sanguinicolidae) from five families of tropical Indo-Pacific fishes

A survey of Pacific coral reef fishes for sanguinicolids revealed that two species of Lutjanidae (Lutjanus argentimaculatus, L. bohar), six species of Siganidae (Siganus corallinus, S. fuscescens, S. lineatus, S. margaritiferus, S. punctatus, S. vulpinus), seven species of Chaetodontidae (Chaetodon aureofasciatus, C. citrinellus, C. flavirostris, C. lineolatus, C. reticulatus, C. ulietensis, C. unimaculatus), three species of Scombridae (Euthynnus affinis, Scomberomorus commerson, S. munroi) and three species of Scaridae (Chlorurus microrhinos, Scarus frenatus, S. ghobban) were infected with morphologically similar sanguinicolids. These flukes have a flat elliptical body, a vestigial oral sucker, a single testis, separate genital pores and a post-ovarian uterus. However, these species clearly belong in two genera based on the position of the testis and genital pores. Sanguinicolids from Lutjanidae, Siganidae, Chaetodontidae and Scombridae belong in Cardicola Short, 1953; the testis originates anteriorly to, or at the anterior end of, the intercaecal field and does not extend posteriorly to it, the male genital pore opens laterally to the sinistral lateral nerve chord and the female pore opens near the level of the ootype ( may be anterior, lateral or posterior to it) antero-dextral to the male pore. Those from Scaridae are placed in a new genus, Braya; the testis originates near the posterior end of the intercaecal field and extends posteriorly to it, the male pore opens medially at the posterior end of the body and the female pore opens posterior to the ootype, antero-sinistral to the male pore. The second internal transcribed spacer (ITS2) of ribosomal DNA from these sanguinicolids and a known species, Cardicola forsteri Cribb, Daintith & Munday, 2000, were sequenced, aligned and analysed to test the distinctness of the putative new species. Results from morphological comparisons and molecular analyses suggest the presence of 18 putative species; 11 are described on the basis of combined morphological and molecular data and seven are not because they are characterised solely by molecular sequences or to few morphological specimens (n= one). There was usually a correlation between levels of morphological and genetic distinction in that pairs of species with the greatest genetic separation were also the least morphologically similar. The exception in this regard was the combination of Cardicola tantabiddii n. sp. from S. fuscescens from Ningaloo Reef ( Western Australia) and Cardicola sp. 2 from the same host from Heron Island ( Great Barrier Reef). These two parasite/ host/location combinations had identical ITS2 sequences but appeared to differ morphologically ( however, this could simply be due to a lack of morphological material for Cardicola sp. 2). Only one putative species ( Cardicola sp. 1) was found in more than one location; most host species harboured distinct species in each geographical location surveyed ( for example, S. corallinus from Heron and Lizard Islands) and some ( for example, S. punctatus, S. fuscescens and Chlorurus microrhinos) harboured two species at a single location. Distance analysis of ITS2 showed that nine species from siganids, three from scombrids and five from scarids formed monophyletic clades to the exclusion of sanguinicolids from the other host families. Cardicola milleri n. sp. and C. chaetodontis Yamaguti, 1970 from lutjanids and chaetodontids, respectively, were the only representatives from those families that were sequenced. Within the clade formed by sanguinicolids from Siganidae there wasa further division of species; species from the morphologically similar S. fuscescens and S. margaritiferus formed a monophyletic group to the exclusion of sanguinicolids from all other siganid species.