Evidence of stability in a chondrichthyan population: case study of the spotted ratfish Hydrolagus colliei (Chondrichthyes: Chimaeridae)

Results presented here provide evidence of an exception to the generalization that all chondrichthyan populations are especially vulnerable to exploitation to the extent that they remain at low abundance for a protracted or indefinite duration even after exploitation rates are reduced. Delta log-normal generalized linear models (GLM) and cluster analysis of fishery-independent catch-per-unit-effort (CPUE) data from 1977 to 2006 indicated the presence of at least two distinct stocks of spotted ratfish Hydrolagus colliei off the U.S. West Coast. CPUE of the continental slope and northern continental shelf and upper slope populations did not vary between 1977 and 1995 and increased from 1995 to 2006. On the basis of the timing of these changes, it is likely that both fishing and climate influenced these trends. Sex and size-specific differences in bathymetric distribution, along with the identification of nursery sites, indicate that fishery by-catch could have a significant effect on population growth. These aggregative behaviours, combined with low fecundity, indicate that H. colliei may be vulnerable to irreversible population depletion by fisheries mortality. Temporal abundance trends indicated, however, that their population size has increased significantly within the last decade, a demonstration of population stability. A literature review indicated that there is also evidence for population stability in other chondrichthyans. The paradigm that all chondrichthyan populations fail to rebuild in response to exploitation, therefore, may not be as broadly applicable as previously thought. Thus, it is not necessarily sufficient to make generalizations regarding the vulnerability of chondrichthyans across higher taxonomic scales.     

The role of a Sertoli cell actin-myosin system in sperm bundle formation in the ratfish, Hydrolagus colliei (Chondrichthyes, Holocephali)

Sertoli cells in the ratfish entirely surround a clone of spermatids to form a spermatocyst. As spermiogenesis proceeds within the cyst cavity, the acrosome areas become apposed to the Sertoli cell plasma membrane lining the spermatocyst. The spermatids elongate and are gathered into an increasingly compact bundle oriented with acrosomal tips directed toward the Sertoli cell base. As all acrosome areas move closer together, Sertoli cell microfilaments oriented parallel to the long spermatid axis appear and increase in concentration. Actin and myosin were demonstrated in the microfilament area with fluorescent antibodies and NBD-Phallacidin. Simultaneously, endocytosis of Sertoli cell membrane between spermatid attachment sites removes the intervening membrane and allows the latter sites to approach each other. Sertoli cell endocytosis is spatially and temporally related to a unique projection at the basal rim of each acrosome. During midspermiogenesis, structured intercellular material appears between the Sertoli cell and the acrosomal region of each spermatid. Its periodicity is closely related to periodic arrangement of Sertoli cell actin and material within the spermatids. These attachment sites move together upon endocytosis, gathering a clone of spermatids into a closely packed bundle.     

Body fluid osmolytes and urea and ammonia flux in the colon of two chondrichthyan fishes, the ratfish, Hydrolagus colliei, and spiny dogfish, Squalus acanthias

The present study has examined the role of the colon in regulating ammonia and urea nitrogen balance in two species of chondrichthyans, the ratfish, Hydrolagus colliei (a holocephalan) and the spiny dogfish, Squalus acanthias (an elasmobranch). Stripped colonic tissue from both the dogfish and ratfish was mounted in an Ussing chamber and in both species bi-directional urea flux was found to be negligible. Urea uptake by the mucosa and serosa of the isolated colonic epithelium through accumulation of ¹⁴C-urea was determined to be 2.8 and 6.2 fold greater in the mucosa of the dogfish compared to the serosa of the dogfish and the mucosa of the ratfish respectively. Furthermore, there was no difference between serosal and mucosal accumulation of ¹⁴C-urea in the ratfish. Through the addition of 2 mM NH₄Cl to the mucosal side of each preparation the potential for ammonia flux was also examined. This was again found to be negligible in both species suggesting that the colon is an extremely tight epithelium to the movement of both urea and ammonia. Plasma, chyme and bile fluid samples were also taken from the agastric ratfish and were compared with solute concentrations of equivalent body fluids in the dogfish. Finally molecular analysis revealed expression of 3 isoforms of the urea transport protein (UT) and an ammonia transport protein (Rhbg) in the gill, intestine, kidney and colon of the ratfish. Partial nucleotide sequences of the UT-1, 2 and 3 isoforms in the ratfish had 95, 95 and 92% identity to the equivalent UT isoforms recently identified in another holocephalan, the elephantfish, Callorhinchus milii. Finally, the nucleotide sequence of the Rhbg identified in the ratfish had 73% identity to the Rhbg protein recently identified in the little skate, Leucoraja erinacea.     

Contribution to the molecular phylogenetic analysis of extant holocephalan fishes (Holocephali, Chimaeriformes)

Much attention has been paid to the molecular phylogeny of holocephalan fishes during recent years, but sampling was very low and not all genera were examined. This study offers an extended sampling of species from all known genera to clarify their phylogeny and to provide an estimate of the time of origin of extant holocephalan taxa. Three mitochondrial genes (cytochrome b, 12S rRNA, and 16S rRNA) were sequenced and analysed using a variety of phylogenetic methods (Bayes, maximum likelihood, and maximum parsimony). Callorhinchidae diverged from Rhinochimaeridae and Chimaeridae about 187?Ma ago. Chimaeridae and Rhinochimaeridae diverged from each other about 159?Ma ago. Within Rhinochimaeridae, Neoharriotta is the sister genus to the closely related Harriotta and Rhinochimaera. Eight species of the family Chimaeridae, belonging to the genera Hydrolagus and Chimaera, were examined. They probably had a common ancestor about 107?Ma ago and appear paraphyletic. These results indicate that the traditional morphological generic definition of the families Rhinochimaeridae and Chimaeridae has to be reinvestigated.     

Ultrastructure and ATPase activity of the rectal gland of the chondrichthyean fish Hydrolagus colliei (Holocephali)

Summary The anatomy, histology, ultrastructure and ATPase activity of the intramural rectal gland of the chondrichthyean Hydrolagus colliei, are described. The cells of the rectal gland of Hydrolagus demonstrate the same well developed lateral and basal cisternae, elongate mitochondria and luminal border as those of their elasmobranch counterparts. ATPase activity within the rectal gland of Hydrolagus is as intense as that in a number of elasmobranchs examined in the course of the study. Despite its primitive intramural location the rectal gland of Hydrolagus respresents a homolog of the more specialized and better known elasmobranch gland and appears as well suited for cation excretion.     

Biological activity of a bombesin-like peptide extracted from the intestine of the ratfish, Hydrolagus colliei.

1. Ratfish (Hydrolagus colliei) intestines were boiled in water to inactivate proteases and then treated with cold 4% trifluoroacetic acid to extract bombesin-like peptides. 2. The extract was fractionated in several steps using reverse-phase and ion exchange HPLC, and bombesin-like immunoreactive peptides were detected by radioimmunoassay using an antiserum specific for the bioactive C-terminal region of bombesin. 3. A highly purified bombesin-like peptide-containing fraction stimulated amylase release in a dose-responsive fashion from rat pancreatic acini; the dose-response curve was parallel to a bombesin standard, and the ratfish peptide stimulated the same maximal rate of amylase secretion as the bombesin standard. 4. A potent, highly selective bombesin receptor antagonist completely abolished the stimulation of amylase release caused by the ratfish peptide, demonstrating the specificity of the response. 5. Estimates of the bombesin-like peptide concentration of this fraction by radioimmunoassay and by bioassay were nearly identical, indicating that ratfish bombesin is very similar biologically and antigenically to frog skin bombesin.     

An investigation of carbonic anhydrase activity in the gills and blood plasma of brown bullhead (Ameiurus nebulosus), longnose skate (Raja rhina), and spotted ratfish (Hydrolagus colliei)

Separated plasma and whole blood non-bicarbonate buffering capacities, together with plasma and gill carbonic anhydrase activities and endogenous plasma carbonic anhydrase inhibitor activity were investigated in three species of fish: the brown bullhead (Ameirus nebulosus), a teleost; the longnose skate (Raja rhina), an elasmobranch; and the spotted ratfish (Hydrolagus colliei), a chimaeran. The objective was to test the hypothesis that species possessing gill membrane-bound carbonic anhydrase and/or plasma carbonic anhydrase activity would also exhibit high plasma nonbicarbonate buffering capacity relative to whole blood non-bicarbonate buffering capacity and would lack an endogenous plasma carbonic anhydrase inhibitor. Separated plasma non-bicarbonate buffering capacity constituted > or = 40% of whole-blood buffering in all three species. In addition, all species lacked an endogenous plasma carbonic anhydrase inhibitor. Separated plasma from skate and ratfish contained carbonic anhydrase activity, whereas bullhead plasma did not. Examination of the subcellular distribution and characteristics of branchial carbonic anhydrase activity revealed that the majority of branchial carbonic anhydrase activity originated from the cytoplasmic fraction in all species, with only 3-5% being associated with a microsomal fraction. The microsomal carbonic anhydrase activity of bullhead and ratfish was significantly reduced by washing, indicating the presence of carbonic anhydrase activity that was not integrally associated with the membrane pellet, microsomal carbonic anhydrase activity in skate was unaffected by washing. In addition, microsomal carbonic anhydrase activity from skate and ratfish but not bullhead gills was released to a significant extent from its membrane association by treatment with phosphatidylinositol-specific phospholipase C. The results obtained for skate are consistent with published data for dogfish, suggesting that the possession of branchial membrane-bound carbonic anhydrase activity may be a generalised elasmobranch characteristic. Ratfish, which also belong to the class Chondrichthyes, exhibited a similar pattern. Unlike skate and ratfish, bullhead exhibited high plasma non-bicarbonate buffering capacity and lacked an endogenous carbonic anhydrase inhibitor in the absence of plasma and gill membrane-bound carbonic anhydrase activities.     

Gonadotropin-releasing hormone in ratfish (Hydrolagus colliei): distribution between the sexes and possible relationship with chicken II and salmon II forms

1. Brain extract from the spotted ratfish, Hydrolagus colliei, contains gonadotropin-releasing hormone (GnRH)-like peptides in both sexes. 2. The dominant form occurs with a concentration of 0.5-1.7 ng/g frozen brain tissue in males, and 1.3-2.5 ng/g in females. 3. A similar pattern of GnRH immunoreactivity and chromatographic behaviour are found in both sexes. 4. A semipurified extract of this peptide could not be distinguished chromatographically from either chicken II or salmon II forms of the peptide. 5. The ratfish represents the most primitive organism that contains a form of GnRH that coelutes with chicken II and salmon II GnRH.     

The leopardChimaera, a new species of chimaeroid fish from New Zealand (Holocephali, Chimaeriformes, Chimaeridae)

A new species ofChimaera is described from three specimens collected from deep water fishing grounds off the North Island of New Zealand at depths ranging from 327–1020 m. This species is distinguished from all other members of the genus by gray coloration with chocolate brown reticulations and spots covering the body and fins, as well as additional external features such as rounded pelvic fins, first dorsal fin with distinct white margin, preopercular and oral lateral line canals sharing a common branch, and morphology of pelvic claspers in males bifid, the distal 1/3 divided, with pale colored fleshy, distal lobes. Comparisons are made toC. monstrosa andC. owstoni, the two most similar species in the genus. this represents the first species ofChimaera to be described from New Zealand.     

Two new species of Chimaericola Brinkmann (Monogenea: Chimaericolidae) from Hydrolagus spp. (Chimaeriformes: Chimaeridae) in the Pacific

Chimaericola ogilbyi n. sp. and C. colliei n. sp. are proposed for chimaericolids found on the gills of the ghost shark, Hydrolagus ogilbyi taken off the coast of southeastern Australia, and the ratfish, H. colliei, taken off the coast of Vancouver Island, respectively. Supplementary observations on C. leptogaster, the type-species of the genus Chimaericola, are included. The two new species are differentiated on the size and shape of the median sucker sclerite, hamuli, spines of the male copulatory apparatus and eggs. Amended diagnoses for the family Chimaericolidae and genus Chimaericola are provided.     

Callorhynchocotyle hydrolagi n. sp. (Monogenea: Hexabothriidae) from Hydrolagus ogilbyi (Chimaeriformes: Chimaeridae) in the South Pacific

Callorhynchocotyle hydrolagi n. sp. is proposed for hexabothriids found on the gills of the ghost shark, Hydrolagus ogilbyi, taken off the coast of southeastern Australia. The species is distinguished from the three previously described species of the genus in that the sclerites and the points of the sclerites of the three sucker pairs are all of similar size. The greater thickness of the sucker sclerites, the hamuli with inflated, almost spherical terminations of the roots, and the robust male copulatory complex also serve to differentiate C. hydrolagi.     

Two new species of chimaeroid fishes from the southwestern Pacific Ocean (Holocephali, Chimaeridae)

 Two new species of chimaeroid fishes from the family Chimaeridae are described on the basis of morphological characters. The carpenter's chimaera is a large-bodied species of Chimaera distinguished from its congeners by massive head with blunt snout; firm, nondeciduous skin; purplish color; preopercular and oral lateral line canals branching together; and pelvic claspers that are divided for the distal one third of length, purple at the base with white fleshy tips. The pale ghost shark is a species of Hydrolagus distinguished from its congeners by a dorsal fin spine that reaches to the origin of the second dorsal fin when depressed; elongate second dorsal fin not indented along its length; preopercular and oral lateral line canals sharing a common branch; long, stout caudal filament; and pale silvery-gray coloration fading to white ventrally. The pale ghost shark has long been recognized as a new species from New Zealand, and formal taxonomic recognition of this species will prove important for fishery management. Received: October 15, 2001 / Revised: May 1, 2002 / Accepted: May 29, 2002 Acknowledgments I am grateful to Peter Last, Alastair Graham (CSIRO, Dept. of Marine Research), Clive Roberts, Andrew Stewart (NMNZ, Wellington), and Mark McGrouther and Doug Hoese (AMS, Sydney), for their hospitality and support of this research. This work was funded by grants from the National Science Foundation (NSF DEB-9510735) and the National Geographic Society (no. 5414–95), and also funded in part by the New Zealand Foundation for Scientific Research and Technology, Biosystematics of NZ EEZ Fishes Project, contract MNZ603, C. Roberts, program leader.     

A review of the sensory biology of chimaeroid fishes (Chondrichthyes; Holocephali)

The chimaeroid fishes (Chondrichthyes: Holocephali) are a small, ancient and poorly studied group of cartilaginous fishes that have puzzled and intrigued taxonomists, ichthyologists and evolutionary biologists for over 100 years. Like their close relatives, the elasmobranchs (sharks, skates and rays), chimaeroids possess an extensive battery of sense organs that allow them to detect information about the external environment in order to find mates, locate food and preferred habitats and avoid predators. In recent years the sensory systems of elasmobranchs have received an up-swell of attention from biologists, which has resulted in a greater understanding of the sensory capabilities and behaviour of these fishes. However, very little recent work has been done on the chimaeroids. The aim of this review is to provide a survey of the existing literature on the major senses (vision, smell, taste, mechanoreception, hearing and electroreception) in chimaeroids, in order to stimulate and identify areas for future research. In chimaeroids information on sensory systems is largely restricted to one or two species (with the exception of some aspects of the visual system) and for some sensory systems essentially nothing is known. Most studies are anatomical in nature and so there is a demand for a greater degree of neurophysiological and behavioural assessment of sensory capability in these fishes. The majority of chimaeroids occupy deep-sea habitats and are becoming increasingly threatened by the expansion of deep-sea fisheries, so an understanding of the sensory biology and behaviour of chimaeroids may be important for the protection and management of these fascinating fishes.     

Social organization of the spotted sharpnose puffer,Canthigaster punctatissima (Tetraodontidae)

Synopsis Tagged individuals of the Eastern Pacific sharpnose puffer, Canthigaster punctatissima, were studied at Punta Santa Inez, Baja California Sur. Territories were maintained by both sexes in this sexually dimorphic fish. Male puffers appear to have harems; one large male interacts with one to four smaller females. Puffers from different harems were not seen to interact except for occasional aggressive contact. Removal of a male puffer resulted in the overnight takeover of his harem by a neighboring male. Harem-forming behavior is discussed, as well as the possible role of predation.     

Mechanisms of vasodilation in the dorsal aorta of the elephant fish, <Emphasis Type="Italic">Callorhinchus milii</Emphasis> (Chimaeriformes: Holocephali)

This study investigated vasodilator mechanisms in the dorsal aorta of the elephant fish, Callorhinchus milii, using anatomical and physiological approaches. Nitric oxide synthase could only be located in the perivascular nerve fibres and not the endothelium of the dorsal aorta, using NADPH histochemistry and immunohistochemistry. In vitro organ bath experiments demonstrated that a NO/soluble guanylyl cyclase (GC) system appeared to be absent in the vascular smooth muscle, since the NO donors SNP (10⁻⁴ mol l⁻¹) and SIN-1 (10⁻⁵ mol l⁻¹) were without effect. Nicotine (3 × 10⁻⁴ mol l⁻¹) mediated a vasodilation that was not affected by ODQ (10⁻⁵ mol l⁻¹), l-NNA (10⁻⁴ mol l⁻¹), indomethacin (10⁻⁵ mol l⁻¹), or removal of the endothelium. In contrast, the voltage-gated sodium channel inhibitor, tetrodotoxin (10⁻⁵ mol l⁻¹), significantly decreased the dilation induced by nicotine, suggesting that it contained a neural component. Pre-incubation of the dorsal aorta with the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP_8–37 (10⁻⁶ mol l⁻¹) also caused a significant decrease in the nicotine-induced dilation. We propose that nicotine is mediating a neurally-derived vasodilation in the dorsal aorta that is independent of NO, prostaglandins and the endothelium, and partly mediated by CGRP.     

Ontogenesis of catabolic and energy metabolism capacities during the embryonic development of spotted wolffish (Anarhichas minor)

The catabolic and energy metabolism capacities during spotted wolffish (Anarhichas minor) embryogenesis were investigated. We assessed the embryo's ability to catabolize proteins (trypsin-like proteases) and lipids (triglyceride lipase) and examined the development of metabolic capacities using enzymatic assays: ability to use carbohydrates (pyruvate kinase), amino acids (aspartate aminotransferase) and fatty acids (hydroxyacyl-CoA dehydrogenase) for energy production, and aerobic (citrate synthase) and anaerobic (lactate dehydrogenase) energy production. Functional enzymatic systems were detected from the eyed stage (350 degree-days), except for fatty acids, which was detected from 540 degree-days. To compare the development of 1) aerobic and anaerobic pathways and 2) the capacity to mobilize the different energy substrates, enzymatic ratios were calculated. Anaerobic capacity appeared to increase at a significantly higher rate than the aerobic capacity. Ratios revealing the relative capacity to use specific energy substrates showed a significantly slower increase during development in the capacity to use carbohydrates than amino acids and fatty acids. The end of embryogenesis was characterized by a significant decrease in the use of carbohydrates for aerobic energy production but an increasing capacity to use amino acids. Egg survival as affected by the variability in metabolic parameters is discussed.     

Correction to: Metabolic growth hypothesis for the evolution of the nuchal hump in swordtail fishes

Environmental Biology of Fishes -