Age determination of orange roughy,Hoplostethus atlanticus (Pisces: Trachichthyidae) using210Pb:226Ra disequilibria

Natural levels of²¹⁰Pb:²²⁶Ra in otoliths of orange roughy,Hoplostethus atlanticus, from south-east Australian waters, were measured to determine fish ages radiometrically. Up to maturity, radiometric age estimates were consistent with a single constant otolith growth rate. Radiometric ages for juveniles were comparable with, but greater than, those obtained in a recent, validated New Zealand study which employed counts of annuli on the surface of otoliths. Beyond maturity, radiometric ages were obtained by modelling with an otolith growth rate set at 45% of the juvenile rate. Radiometric ageing confirms that orange roughy is very slow-growing, with an age at maturity (32 cm standard length, SL) of ~ 32 yr, and is very long-lived, with fish 38 to 40 cm being 77 to 149 yr old. These results have important implications for the management of the fishery.     

Morphometric and meristic comparison of orange roughy (Hoplostethus atlanticus: Trachichthyidae) from the Puysegur Bank and Lord Howe Rise,New Zealand,and its implications for stock structure

Significant morphological differences were found between orange roughy, Hoplostethus atlanticus, caught in 1993 on the Puysegur Bank and those caught on the Lord Howe Rise, New Zealand. A total of 17 separate body measurements and counts were taken from each fish. Treating the sexes separately, significant differences were found between sites when linear relations between eight particular body measures and standard length were compared. The eight measures indicating differences in shape were head length, snout length, orbit diameter, maxilla width, premaxilla length, caudal peduncle, gill raker count, and anal fin count. Discriminant functions were used to compare sites and sexes, and these permitted a >90% success rate in distinguishing fish from the two sites. A discriminant function could not be found which successfully separated two separate tows made on the Puysegur Bank, indicating that phenotypic differences do not vary as much within a site as they do between sites. All analyses made suggested that fish from the two different areas had different body shapes. Morphological differences, such as those found in the current investigation, could only arise if the fish populations from the two areas were relatively discrete. There may be some movement of fish between areas, quite possibly enough to bring about relative genetic homogeneity, but clearly there is insufficient to prevent the two populations from differing phenotypically. These differences suggest that morphometric analysis may be a useful tool for distinguishing New Zealand orange roughy stocks.     

Stock discrimination of orange roughy,Hoplostethus atlanticus,by parasite analysis

Seasonal changes of respiratory metabolism and biochemical composition were studied in Actinia equina L. (Cnidaria: Anthozoa) collected in 1982 and 1983 from two shore locations in Spain. Changes of metabolic activity follow closely those of biochemical constituents, particularly carbohydrates and lipids, showing maxima in late fall and spring. Weight dependence, established according to the exponential equation y=a x^b (x=weight), results in virtually isometric relationships for proteins, total lipids and sugars but not glycogen. Allometry for this last compound represents a reduction in glycogen level in connection with size decrease; this weight effect declines when glycogen levels rise, both in field and laboratory fed anemones, thus suggesting a stronger influence of food availability on storage in small anemones.     

Allozyme and mitochondrial DNA variation in orange roughy,Hoplostethus atlanticus (Teleostei: Trachichthyidae): little differentiation between Australian and North Atlantic populations

Allozyme and mitochondrial DNA (mtDNA) genetic variation was compared in orange roughy (Hoplostethus atlanticus Collett) collected from waters off southern Australia and from waters about 22 000 km away in the North Atlantic west of Scotland. Samples were screened for 11 polymorphic allozyme loci and with 9 restriction enzymes. Significant heterogeneity between the two areas was detected for three allozyme loci (ADA ^*, CK ^* and GPI-1 ^*), and the overall G _ST (gene-diversity statistic) value of 1% was small but significant. Significant mtDNA haplotype heterogeneity was observed after ²- of haplotype frequencies but not after a G _ST analysis. Nucleotide sequence-diversity analysis showed very low net divergence (0.0023%) between the two samples. The Australian orange roughy had a lower allozyme heterozygosity and a lower mitochondrial DNA nucleon diversity than the North Atlantic sample. The very limited, although significant, allozyme and mitochondrial DNA heterogeneity between these areas suggests that there is some gene flow between these two populations. The species appears to be widespread, with its presence reported from the southern Pacific, southern Indian, and northern and southern Atlantic Oceans, and it is likely that gene flow between the antipodes is mediated by stepping-stone exchange between adjacent populations rather than by direct migration.     

DNA fingerprints of orange roughy,Hoplostethus atlanticus: a population comparison

Genetic variability among Hoplostethus atlanticus collected from two spawning grounds east and west of New Zealand was examined using DNA fingerprints as revealed by hybridization with three clonal probes: 33.15, M13 and 3HVR. The 33.15 and 3HVR fingerprints revealed a complex pattern of restriction fragments, apparently refecting a multi-locus system of highly variable minisatellite alleles similar to the pattern of alleles reported in other vertebrates. The M13 fingerprints revealed a distinct pattern of restriction fragments of high molecular weight, reflecting a single-locus system that overlapped with the family of minisatellite alleles observed in 33.15 fingerprints. In a sample of 12 orange roughy collected on a single regional spawning site, the average percent similarity of 33.15 fingerprints was 21.15% (SD=17.75), the average percent similarity of 3HVR fingerprints was 14.32% (SD=14.45) and the inferred average allelic frequency of the M13 single-locus system was 0.071. A comparison of 33.15 and M13 fingerprints from two distant spawning sites ground New Zealand revealed no obvious regional differences. The variability of orange roughy fingerprints was so great, however, that regional comparisons could not be considered conclusive indicators of genetic identity. Our results provide a preliminary assessment of the power and pitfalls of using DNA-level markers for the population analysis of marine fish.     

Evidence of stock separation in southern hemisphere organge roughy (Hoplostethus atlanticus,Trachichthyidae) from restriction-enzyme analysis of mitochondrial DNA

Restriction enzyme analysis of mitochondrial DNA (mtDNA) was used to test for genetic homogeneity of orange roughy (Hoplostethus atlanticus) in the southern hemisphere. Two hundred and eighty-six orange roughy specimens were collected from seven general localities: the Great Australian Bight; South Australia (off southeastern Kangaroo Island); the west coast of Tasmania; the east coast of Tasmania; New South Wales; New Zealand and South Africa. Mitochondrial DNA was extracted from developing ovary tissue and analysed with 10 six-base enzymes and 3 four-base enzymes. Both forms of analysis revealed a low level of genetic diversity in this species. The six-base enzyme study found no evidence of reproductively isolated populations of orange roughy in southeastern Australian waters. However, an analysis of 107 fish with 3 four-base enzymes identified at least partial genetic separation of the New South Wales (NSW) sample of orange roughy from South Australian (off southeastern Kangaroo Island) and Tasmanian samples. This finding supports biological evidence for the presence of a distinct subpopulation of orange roughy in NSW waters. The four-base study also provided evidence of the presence of genetically distinct samples of orange roughy occurring in the same localities off southeastern Kangaroo Island from consecutive years. Additional sampling and the use of a greater number of four-base enzymes may be needed to determine if any genetic structuring exists among orange roughy south of New South Wales.     

Transition zone in otoliths of orange roughy (Hoplostethus atlanticus) and its relationship to the onset of maturity

A transition zone in the otoliths of orange roughy (Hoplostethus atlanticus) is described where annulus width decreases markedly. For fish sampled at spawning time, the relationship between gonad stage and the presence or absence of a transition zone is consistent with the hypothesis that this zone marks the onset of maturity, if allowance is made for some error in gonad staging and identification of the zone. Another data set from a non-spawning area after the spawning season is not consistent with the hypothesis. However, these latter data are considered less reliable because of the small size of the fish in the sample and difficulties in determining, outside the spawning season, whether a fish has been reproductively active. This hypothesis was used to provide estimates of the median age (30 yr) and length (31 cm) at the onset of maturity for the Chatham Rise, New Zealand population. These estimates are unaffected by the biases associated with the usual ogive method of estimation. Received: 27 June 1997 / Accepted: 1 July 1997     

Wax-ester metabolism in the orange roughyHoplostethus atlanticus (Beryciformes: Trachichthyidae)

Freshly caught orange roughy (Hoplostethus atlanticus) obtained at the edge of the Chatham Rise, east of the South Island of New Zealand, in June 1988, were used to investigate tissue-specific lipid synthesis and to obtain blood for plasma lipoprotein analysis. Tissue slices prepared from an intraneurocranial fat deposit, pieces of skull (neurocranium), swimbladder and liver were incubated with radioactive acetate, palmitate and oleate, and the labelled lipids extracted and analysed. All four tissues could incorporate acetate label into fatty acids which were themselves incorporated into triacylglycerols and phospholipids although not into wax esters, the most abundant lipid class in these tissues. Exogenous palmitate and oleate were also incorporated into more complex lipids, with the label from oleate (but not palmitate) being found in wax esters as well as triacylglycerols and phospholipids. The distribution of the label in the wax esters showed that some reduction of the fatty acid to fatty alcohol had occurred. The only exception to this pattern was the swimbladder, which incorporated small amounts of palmitate-label into both the fatty acid and fatty alcohol portions of the wax esters. Lipoproteins were isolated from serum by centrifugation. All lipoprotein classes contained phospholipid, cholesterol, triacylglycerol, cholesteryl esters and wax esters. A very low-density lipoprotein class also contained large amounts of unesterified fatty acids, which are possibly artefacts resulting from storage of the samples. Significant quantities of-3 fatty acids were also found in the serum lipids.     

Between-area differences in age and length at first maturity of the orange roughy Hoplostethus atlanticus

Mean age and length at onset of maturity were estimated for orange roughy (Hoplostethus atlanticus) populations off New Zealand, Namibia, and Great Britain. Significant between-area differences were apparent in both these parameters. Implications of the between-area differences on stock structure of orange roughy in New Zealand waters are discussed. A proportional relationship between age at onset of maturity and modal size of fish in the mature population is demonstrated. This is consistent with later-maturing fish experiencing a longer period at a pre-maturity growth rate that is relatively faster than the rate of somatic growth after maturity. Received: 22 December 1997 / Accepted: 5 May 1998     

Population structure and life history of orange roughy (Hoplostethus atlanticus) in the SW Pacific: inferences from otolith chemistry

We examined site differences in the elemental composition of the primordium and ontogenetic variability of Sr in otoliths of fish from Australia and New Zealand and, as an out-group, the North Atlantic. Differences among sites in primordium composition are slight, but significant for all five elements assayed (Sr, Pb, Cu, Zn and Hg), but principally reflect differences between the North Atlantic and SW Pacific specimens, do not replicate for independent samples in the SW Pacific and constitute a poor “natural tag” in roughy, with <25% of fish successfully assigned to source location. However, mean Sr weight-fractions at the primordium showed similar latitudinal variation across sites in Australia, New Zealand and the Tasman Sea, indicating both spatially structured populations and a common structuring process across the region. Comparisons of ontogenetic variability of Sr in otoliths from juveniles and young adults within and between sites in the SW Pacific strongly support the hypothesis that variability in this element is site-specific and environmentally sensitive, although the environmental factors involved are not obvious. The otolith analysis confirms previous suggestions that juvenile and adult Hoplostethus atlanticus are relatively sedentary, but also indicates that the population sub-structuring by age within sites is more complex and there are likely to be more spawning areas in Australian waters than previously thought. More broadly, although single point analysis of otolith composition at the primordium resolves a population structure in roughy, alone it is not precise enough to test hypotheses about the processes causing this structure. Ontogenetic variability in Sr provides better resolution of spatial structure, even in a relatively homogenous marine environment like the deep ocean, and also provides insight into behavioural and ecological factors. Ontogenetic analyses of Sr in otoliths are expensive to obtain, require more effort in specimen preparation than single point analyses, and are difficult to compare statistically, but the increased information they yield warrants their broader consideration in marine species.     

Genetically isolated stocks of orange roughy (Hoplostethus atlanticus), but not of hoki (Macruronus novaezelandiae), in the Tasman Sea and Southwest Pacific Ocean around New Zealand

Restriction fragment-length polymorphisms of mitochondrial (mt) DNA, generated by six-base restriction enzymes, were used to examine the stock structure of the two major commercial species in New Zealand fisheries, orange roughy (Hoplostethus atlanticus Collett) and hoki (Macruronus novaezelandiae Hector). Samples of orange roughy from six spawning sites around New Zealand and one site off Tasmania show significant genetic heterogeneity. Samples from two sites around the south of New Zealand were genetically similar to each other, but dissimilar to samples from all other sites. The common haplotype observed in northern sites was absent from the two southern sites. Low numbers of unique haplotypes were restricted to the Challenger Plateau in the Tasman Sea. There was no significant genetic heterogeneity in five samples of hoki from two spawning sites off New Zealand and one site off Tasmania.     

Population variation in the mitochondrial cytochrome b gene of the orange roughy Hoplostethus atlanticus and the hoki Macruronus novaezelandiae

To describe the genetic relationship among regional populations of two commercially valuable species of marine fish, the orange roughy Hoplostethus atlanticus and the hoki Macruronus novaezelandiae, the mitochondrial (mt) DNA haplotypes of 59 individuals were defined by direct sequencing of the cytochrome b gene. Samples of orange roughy were collected on four fishing grounds around New Zealand, one off the west coast of Tasmania and one near South Africa from 1990–1991. Samples from hoki were collected on three fishing grounds around New Zealand and one off Tasmania during the same period. An average of 252 nucleotides were sequenced from each of 32 orange roughy and an average of 372 nucleotides from each of 27 hoki. Sequence variation allowed the definition of 9 unique orange roughy haplotypes and 5 hoki haplotypes. Genetic variation, as measured by both average sequence divergence and haplotype diversity, was high in the orange roughy (nucleotide diversity=0.590%, haplotype diversity=0.782) and low in the hoki (nucleotide diversity=0.076%, haplotype diversity=0.279) relative to a similar survey of the Atlantic cod, Gadus morhua. Differences in haplotype frequencies of orange roughy from New Zealand, Tasmania and South Africa were not significant, and the most common haplotype was found in similar frequencies in these three geographically distant regions. Differences in haplotype frequencies between the New Zealand and Tasmanian samples of hoki were significant, suggesting restricted gene flow between these two regions. The contrasting patterns of low but regionally subdivided genetic variation in the hoki versus high but geographically undifferentiated genetic variation in the orange roughy may be attributed to the low fecundity, slow maturation and long lifespan of the orange roughy relative to the hoki.     

Role of wax esters in determining buoyancy inHoplostethus atlanticus (Beryciformes: Trachichthyidae)

Specimens of the orange roughyHoplostethus atlanticus were caught at the edge of the Chatham Rise, east of the South Island of New Zealand, in June 1988, during a commercial fishing voyage. Several tissues of the fish were found to contain large quantities of lipid almost entirely as wax esters. These tissues include a fat-invested swimbladder, the skin, skull and spine, and a fat-infiltrated tissue found in the neurocranial cavity. The physical properties of the wax esters have been examined relative to the temperatures that exist where the fish are found. Differential scanning calorimetry and NMR spectroscopy both suggest that at 6°C, the temperature at which the fish are located in the water column, the lipid is partially solid. However, at 14°C, the temperature at the surface where the fish are positively buoyant, the lipid is completely liquid. It is proposed that the increased density of the lipid at 6°C would make the fish neutrally buoyant in its normal habitat. The location of the lipidrich tissues has been examined relative to their possible buoyancy contribution, and a histological examination of the swimbladder has been performed.     

New morphological characteristic of Xyrichtys novacula (Pisces: Labridae) from the Adriatic Sea

In 1983 curred horns were detected in the rare Adriatic Sea fish Xyrichtys novacula (Linnaeus, 1758). Their dimensions and histological structures have been investigated. This observation, compared with previous occurrences, suggested the existence of heteromorphism within this species.     

Ecological studies on intertidal New Zealand Sphaeromatidae (Isopoda: Flabellifera)

Ten sympatric rocky shore species and 3 brackish-water species of Sphaeromatidae were studied. Rocky shores were classified in terms of substrate and exposure to wave action. Although most of the rocky-shore species occur on all shore classes, vertical and horizontal distribution in each species, as well as densities, vary with substrate and wave action. A close relationship between distribution and breeding exists in the rocky-shore species; maximum differences in the vertical distribution of juveniles and adults occur, together with the highest reproductive capacities, in the species exposed to the greatest wave action. Tolerances to temperature, salinity and desiccation are wider in the species of brackish water and less exposed rocky shores, correlating with the greater variations in these conditions where wave action is reduced. Exoskeletons and pereopods are stouter in the species of more exposed shores, except where the microhabitat affords protection from wave action. In Isocladus armatus, geographic and seasonal variations in relative frequencies of colour forms correlate with differences in environmental temperatures. Under laboratory conditions, the colour forms show differences in tolerances to temperature and salinity.This work was carried out in the Zoology Department, University of Canterbury, New Zealand; the text was completed in Zoologisches Institut der Universität Kiel, Germany.     

Food selection by laboratory-reared larvae of the scaled sardine Harengula pensacolae (Pisces,Clupeidae) and the bay anchovy Anchoa mitchilli (Pisces,Engraulidae)

Food selection by laboratory-reared larvae of scaled sardines Harengula pensacolae, and bay anchovies Anchoa mitchilli, was compared. Natural plankton was fed to the larvae during the 22 days following hatching. Food levels in the rearing tanks were maintained at an average of 1,600 to 1,800 potential food organisms per liter. Larvae of both species selected as food copepod nauplii, copepodites, and copepods; initial feeding was on organisms of 50 to 75 body width. Larvae of H. pensacolae averaged 4.2 mm in total length at hatching and those of A. mitchilli about 2.0 mm. H. pensacolae larvae grew about 1.0 mm per day and A. mitchilli 0.70 mm per day. The mean number of food organisms in each digestive tract was greater in H. pensacolae than in A. mitchilli, and the difference in number increased as the larvae grew. Average size of food organisms eaten increased for both species with growth, because of selection by the larvae; the average size of copepodites and copepods in digestive tracts increased at a faste rate in H. pensacolae than A. mitchilli. A. mitchilli longer than 8 mm did not eat copepod nauplii.Contribution No. 170, Bureau of Commercial Fisheries Tropical Atlantic Biological laboratory, Miami, Florida 33149, USA.     

Genetic similarity between samples of the orange roughyHoplostethus atlanticus from the Tasman Sea,South-west Pacific Ocean and North-east Atlantic Ocean

Gel electrophoresis was used to measure genetic variation in the orange roughyHoplostethus atlanticus. Samples were collected on the continental slope in the Tasman Sea, South-west Pacific Ocean and North-east Atlantic Ocean, at various periods from 1982 to 1984. Twenty-two enzymatic loci were resolved in seven samples to give observed heterozygosities between 0.104±0.037 and 0.125±0.044. There was little genetic differentiation between populations separated by a distance of approximately 21 000 km. Tasman-Pacific and Atlantic samples differed significantly in allele frequency at only two loci, while at a third locus a rare allele was found only in the Atlantic Ocean.     

A genetic analysis of the pea crabs (Decapoda: Pinnotheridae) of New Zealand

Seven populations of the pea crabPinnotheres atrinicola Page were sampled from around the North Island of New Zealand from February to October 1987, and individuals were scored at 23 presumptive enzymatic loci. For a brachyuran crab,P. atrinicola revealed high levels of polymorphism and heterozygosity. Of the loci scored, phosphoglucose isomerase (Gpi) and phosphoglucomutase (Pgm) were distinguished by high variability ( =0.602 and 0.526, respectively). A clinal variation in electromorph frequency was evident at several loci, and atGpi in particular. Statistical analyses revealed that, despite relatively small genetic distance separation, a high degree of structuring was present between the geographic populations. The degree of population subdivision observed in this study is atypical of brachyuran crabs. It is suggested that the genetic differentiation observed between pea crab populations is maintained by life-history attributes and current movements which restrict gene flow between populations and, to some extent, by random genetic drift.Publication No. 41 from the Evolutionary Genetics Laboratory, University of Auckland     

Effects of Pollinator Loss on Endemic New Zealand Mistletoes (Loranthaceae)

Abstract: The endemic mistletoes Peraxilla colensoi and P. tetrapetala (Loranthaceae) have declined considerably in New Zealand since 1840, reputedly because of introduced herbivores but coincident with a major decline in native bird densities. We show that at two South Island sites ( Craigieburn and Ohau) there are too few bird pollinators visiting the flowers to allow full fruit set. We studied pollination rates in P. colensoi at Wakefield and P. tetrapetala at Craigieburn over four flowering seasons and P. tetrapetala in one season at Ohau. Supplemental hand pollination increased fruit production 1.25–5.3 times at Craigieburn and Ohau but not at Wakefield. Excluding birds by covering mistletoes with mesh bags decreased fruit set significantly at Wakefield but had little effect at Craigieburn and Ohau. Bellbirds ( Anthornis melanura ) and Tuis (   Prosthemadera novaeseelandiae ) visited flowers significantly more often at Wakefield than at Craigieburn. A lack of pollen tubes in the style, not self-incompatibility or resource shortage, caused the low fruit production in unmanipulated flowers at Craigieburn. Thus, at the two P. tetrapetala sites (Craigieburn and Ohau) fruit set was chronically pollen limited, whereas P. colensoi at Wakefield was not pollen-limited. Data from other Peraxilla sites also suggest pollination failure. Our study suggests that the conservation of Peraxilla species will require maintenance of native bird populations. Tuis and Bellbirds are important pollinators and dispersers of many other New Zealand plants, and the breakdown of such mutualistic relationships may have widespread consequences.