Abnormal hermaphroditism in the multispine skate Bathyraja multispinis (Chondrichthyes, Rajidae)

A hermaphroditic individual of the multispine skate, Bathyraja multispinis , caught on the Argentinean continental shelf, is described. This is the first record of hermaphroditism in the genus Bathyraja and one of the very few hermaphroditic specimens reported in the Rajidae.     

Diet of the Antarctic starry skate Amblyraja georgiana (Rajidae, Chondrichthyes) at South Georgia (Southern Ocean)

Stomach contents were identified from 206 Antarctic starry skate (Amblyraja georgiana) that were collected during three groundfish surveys (September 2007, April 2008 and January 2009) at South Georgia, Southern Ocean. The diet of A. georgiana varied with skate size and between years. Preferred prey included fish (particularly for larger individuals) and Antarctic krill, Euphausia superba, as well as amphipods, polychaetes and other benthic fauna. The skate A. georgiana appears to be an opportunistic predator, and the clear presence of Antarctic krill in this demersal predator’s diet may indicate a benthic habit of this euphausiid species, which has hitherto mainly been considered as occupying a purely pelagic niche.     

Avoiding being dragged away: finding egg cases of Schroederichthys bivius (Chondrichthyes: Scyliorhinidae) associated with benthic invertebrates

Egg cases of the narrowmouthed catshark Schroederichthys bivius were recorded entangled with sponges, corals and tubeworms at different sites in the south‐west Atlantic Ocean. This work sheds light on the importance of benthic invertebrates in the life cycle of oviparous chondrichthyan species.     

Reproductive cycles of Mugil cephalus, Liza ramada and Liza aurata (Teleostei: Mugilidae)

Carbohydrates in photoreceptor segments in the retina of the firemouth cichlid Thorichthys meeki are described and compared. The present periodic acid-Schiff (PAS) and lectin results revealed the occurrence of neutral carbohydrates, composed mainly of glycosamine and mannose and glucose, in the light absorbing segments in rods and cones in this species. Unlike in mammals, the retina in this teleost seems to be poor in galactose and galactose-galactosamine units in the light absorbing segments.     

Reproductive biology of Zearaja chilensis (Chondrichthyes: Rajidae) in the south-east Pacific Ocean

Between 2000 and 2002, three artisanal landing sites were sampled in southern Chile, with data on population structure and reproductive development collected from 5477 yellownose skates Zearaja chilensis. Total length (L(T) ) ranged from 33 to 158 cm for females and 34 to 155 cm for males. No sexual dimorphism was evident in disc size (length or width) or in L(T)-mass relationships. The smallest mature female was 95 cm L(T) and the size at which 50% were mature (L(T50) ) was 109 cm. Males matured between 80 and 90 cm L(T) with a L(T50) of 88 cm. Although the largest Z. chilensis captured by the artisanal fishery was 155 cm L(T) , 89% of landings comprised relatively small, immature fish. This situation may compromise the stock integrity if intrinsic vulnerability and probable long-life span of Z. chilensis are considered. Consequences for the survival of the species and possible signs of a fishery collapse must be reviewed by management authorities by consideration of both artisanal and industrial landings in Chile.     

Squalus bassi sp. nov., a new long‐snouted spurdog (Chondrichthyes: Squaliformes: Squalidae) from the Agulhas Bank

The long‐snouted African spurdog Squalus bassi sp. nov. is described based on material collected from the outer shelf and upper continental slope off South Africa and Mozambique. Squalus bassi shares with S. mitsukurii, S. montalbani, S. chloroculus, S. grahami, S. griffini, S. edmundsi, S. quasimodo and S. lobularis a large snout with prenarial length greater than distance between nostrils and upper labial furrows, dermal denticles tricuspidate and rhomboid and elevated number of vertebrae. Squalus bassi can be distinguished from all its congeners by a combination of body and fin colouration, external morphometrics, vertebral counts and shape of dermal denticles. Similar long‐snouted congeners from the Indo‐Pacific region, including S. montalbani, S. edmundsi and S. lalannei are compared in detail with the new species. This new species has been misidentified as the Japanese S. mitsukurii and the Mediterranean S. blainvillei due to the lack of comparative morphological analyses. The validity of the nominal species S. mitsukurii in the south‐eastern Atlantic Ocean and western Indian Ocean is also clarified herein, indicating it has a more restricted geographical distribution in the North Pacific Ocean.     

Reproductive biology of Vinciguerria nimbaria in the equatorial waters of the eastern Atlantic Ocean

Adult Vinciguerria nimbaria in an area of the Atlantic Ocean (0–5°N; 10–20°W), collected from November 1994 to February 1998, exhibited two different patterns in diel behaviour: 'typical' behaviour which consisted of large diel vertical migration and 'atypical', characterized by concentrations of schools that remained in the surface layers during the daytime. The total life span of V. nimbaria was estimated at 6–7 months. Females were mature when they reached 30·6 mm standard length ( L _S), which corresponded to an age of 85 days. Once the females were mature, spawning was continuous in the population as a whole, and V. nimbaria spawned continuously throughout the year. Spawning took place during two restricted times of the day: typical females spawned at dusk and atypical females spawned at dawn. Using the post-ovulatory follicles method, spawning frequency was estimated at 2 days. Batch fecundity was estimated at 1236 oocytes or 1230 oocytes g⁻¹ of total body mass, and egg size was 650 µm whatever the period of the year. The lifetime fecundity of V. nimbaria was estimated at 9000 eggs (109 000 eggs if mortality rate was not taken into account), and the maximum stock egg production of a theoretical cohort occurred at 37 mm L _S. Young adults thus contributed the most to the reproductive output for the survival of the population.     

Effects of intrinsic and extrinsic factors on the diet of Bathyraja macloviana,a benthophagous skate

The effects of intrinsic (sex, maturity stage and body size) and extrinsic (depth and region) factors on the diet of Bathyraja macloviana, in the south‐west Atlantic Ocean, were evaluated using a multiple‐hypothesis modelling approach. Bathyraja macloviana fed mainly on polychaetes followed by amphipods, isopods and decapods. Effects of intrinsic and extrinsic factors on diet composition of this species were found. The consumption of polychaetes had a humped relationship with total length (L_T), and isopods and decapods increased with increasing L_T. Immature individuals preyed on amphipods more heavily than mature individuals. Furthermore, region and depth had an important effect on the consumption of isopods, decapods and amphipods. Such ontogenetic changes and spatial patterns may provide insights into understanding the regulatory mechanisms of marine communities.     

Reproductive biology of the South West Atlantic marbled sand skate Psammobatis bergi Marini, 1932 (Elasmobranchii, Rajidae)

The reproductive biology of Psammobatis bergi was investigated based on 92 males and 136 females skates taken from the coastal bottom trawl fishery at Puerto Quequén, Argentina. The relationship between total body mass and total length (TL) was not significantly different between sexes, but females were heavier than males. Minimum length at maturity in males was 451 mm TL with a length ratio of 74%, whereas females were 415 mm TL with a length ratio of 74%. TL at which 50% of males were mature was 457.6 mm (75.6% of the largest male) and for females was 441.6 mm (79.1% of the largest female). The results indicate a continuous reproductive cycle during the year, with a maximum number of females carrying egg cases in warmer seasons.     

Reproductive characteristics and population decline of four species of skate (Rajidae) off the eastern coast of Canada

Four of the most common species of skate (Rajidae) were studied off eastern Canada to determine if their reproductive characteristics were linked to their population trajectories. The fecundity of the winter skate Leucoraja ocellata , the little skate Leucoraja erinacea , the thorny skate Amblyraja radiata and the smooth skate Malacoraja senta averaged between 41 and 56 egg cases per year for each species. For all species but L. ocellata , males matured at larger sizes and at later ages than females. Theoretical rates of population increase for non-equilibrium populations of L. ocellata ( c . 0·07), M. senta ( c . 0·14) and L. erinacea and A. radiata ( c . 0·20) were low compared to most fishes, indicating that north-west Atlantic skates are intrinsically unproductive, yet are theoretically capable of supporting low-level fisheries. Nevertheless, the results of 36 years of research surveys indicate that the abundance of mature L. ocellata , A. radiata and M. senta all decreased by >90% since 1970, indicating that past fishing mortality (both directed and undirected) has outstripped the net productivity of the skate populations on the eastern Scotian Shelf. The relationship between maximum age ( t _max) and age of maturity ( t _mat) was a better predictor of population growth rate than was body size, with the species exhibiting the highest ratios of t _mat : t _max ( L. ocellata = 0·68, M. senta = 0·66) having the lowest predicted population growth rates. L. ocellata appears to have the lowest productivity and has experienced the greatest population decline, thus raising concerns over its future status.     

Reproductive strategy of the Patagonian catfish Hatcheria macraei

This study describes the reproductive strategy of the stream‐dwelling catfish Hatcheria macraei in the Pichileufu River, Argentina. Gonad maturity phases, classified on the basis of histological analysis, stages of gamete development and the frequency distribution of oocyte size, were correlated with macroscopic features of the gonads. Hatcheria macraei has a cystovarian ovary, asynchronous oocyte development and lobular testes. Five oocyte and four spermatogenic stages were identified and related to macroscopic gonad characteristics, making it possible to divide gonad development into five phases for females and males. Mature oocyte diameter ranged from 922 to 1935 µm. Absolute fecundity in mature females varied from 115 to 480 oocytes. Hatcheria macraei has multiple spawning during a protracted reproductive season that extends from December to April. This, together with its small size, is characteristic of an opportunistic reproductive strategy, commonly found in species that inhabit adverse and unpredictable environments, such as the low‐order rivers of Patagonia.     

Catch composition,reproductive biology and diet of the bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae) from the south‐eastern Arabian Sea

Fishery and biological data are presented for the poorly known bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae), from the deep waters of the south‐eastern Arabian Sea. A total of 5318 individuals from by‐catch landings of deep‐water bottom set longlines, gillnets and shrimp trawl fisheries operating at depths of 200–1200 m were recorded between January 2008 and December 2011 at the Kochi Fisheries Harbour (Kerala). A total of 431 individuals, from 46 to 318 cm total length (L_T) and 0·8 to 132 kg total mass (M_T), were examined to determine biological data for this species. The L_T at which 50% were mature (L_T50) for females and males was estimated at 189 and 187 cm L_T. Litter size ranged from 10 to 36 and size at birth was between 42 and 46 cm L_T. Dietary analysis of stomach contents revealed E. brucus feeds on a variety of prey including crustaceans (69% index of relative importance, I_RI), teleosts (25·8% I_RI), cephalopods (1·7% I_RI) and elasmobranchs (0·7% I_RI). This study provides the first detailed biological data for this species and also highlights the extent of the by‐catch fishery for this species in Indian waters.     

Molecular barcoding of skates (Chondrichthyes: Rajidae) from the southern Northeast Atlantic

Serra‐Pereira, B., Moura, T., Griffiths, A. M., Gordo, L. S. & Figueiredo, I. (2010). Molecular barcoding of skates (Chondrichthyes: Rajidae) from the southern Northeast Atlantic. —Zoologica Scripta, 40, 76–84. Due to their vulnerability to fishing pressure, many species of skate (Rajidae) in the Northeast Atlantic are undergoing declines in abundance. The assessment of stock status and subsequent proposal of management measures are often complicated by high levels of species diversity and endemism, coupled with morphological and ecological conservatism, which makes distinguishing between species difficult. To improve the identification of skates and investigate the phylogenetic position of endemic species the cytochrome c oxidase subunit I (COI) was sequenced in 12 species (Dipturus oxyrinchus, Leucoraja naevus, Leucoraja circularis, Neoraja iberica, Raja brachyura, Raja clavata, Raja maderensis, Raja microocellata, Raja miraletus, Raja montagui, Raja undulata, Rostroraja alba) inhabiting the Portuguese waters. Based on sequence divergence R. maderensis and R. clavata only differ by 1% of the 652 bp COI sequence, questioning the recognition of R. maderensis (considered to be endemic to Madeira and the Azores), as a reproductively isolated species. Otherwise, there was clear phylogenetic support for the different genera and all the remaining species, although the genetic divergence was low compared to other chordates. In particular, COI analysis allowed clear identification of the morphologically similar species R. brachyura and R. montagui.     

Reproductive biology of two sympatric skates in the south‐west Atlantic: Psammobatis rudis and Psammobatis normani

The total lengths ( L _T) at which 50% were mature of Psammobatis rudis and Psammobatis normani , in the south‐west Atlantic were: P. rudis , 428 mm for males and 414 mm for females and P. normani , 443 mm for males and 403 mm for females. Clasper length in mature males was greater in P. normani than in P. rudis , whereas oviducal gland width was not different between species. Females of P. normani with egg cases were found in every month sampled, and in January, March, April and July in P. rudis , although insufficient samples were available to identify peak oviposition times. Geographic variation in size frequency and maturity were found. The effects of oceanographic conditions and fishing pressure are discussed. Size at 50% maturity in both species was >74% of the maximum L _T, indicating late sexual maturity and low potential stock recovery rate.     

Reproductive biology of female big‐bellied seahorses

In this study, ovarian morphology, reproductive condition and sex steroid levels were investigated in the big‐bellied seahorse Hippocampus abdominalis , collected by snorkel and SCUBA diving in Wellington Harbour, New Zealand. Within the ovary, oocytes were contained between an outer muscular wall and an inner layer of luminal epithelium. Two germinal ridges ran along the entire length of the ovary. In cross‐section, oocytes were arranged in sequential order of development beginning at the germinal ridges and ending at the mature edge. Ovarian lamellae were absent. Vitellogenic and advanced cortical alveoli oocytes were elongated in shape, whereas maturing oocytes were distinctively pear‐shaped. Mature oocytes were large (2·6 – 4·4 mm in length) and aligned with the animal pole towards the muscular wall. Reproductively mature females were found throughout the year indicating a protracted reproductive season. The gonado‐somatic index was significantly different between all ovarian stages, but the hepato‐somatic index was not. Females with previtellogenic ovaries had significantly higher plasma concentrations of testosterone than females with vitellogenic or maturing ovaries. There was no significant difference in plasma concentrations of testosterone between females with vitellogenic or maturing ovaries, or in plasma concentrations of 17β‐oestradiol between females in all ovarian stages. This study contributes to the knowledge on the reproductive biology of female syngnathids.     

The potential use of caudal thorns as a non-invasive ageing structure in the thorny skate (Amblyraja radiata Donovan, 1808)

The thorny skate, Amblyraja radiata, is the most widely distributed and abundant of all skate species worldwide, found on both sides of the north Atlantic Ocean. Large inter-regional size differences exist for this species and the few age and growth studies undertaken have revealed marked differences in life history traits for geographically distinct stocks. To facilitate the progression of further age and growth studies for this commercially important species, the effectiveness of caudal thorns as a rapid ageing tool was assessed. Twenty-eight male and 24 female thorny skates were collected off Greenland, covering the full size range of the species. Replicate age readings of crystal violet stained vertebral sagittal sections and whole silver nitrate stained caudal thorns revealed mean intra-reader age reading precision was higher for caudal thorns (Covariance (CV): reader 1 = 9.07, reader 2 = 9.73) than vertebrae (CV: reader 1 = 14.91, reader 2 = 14.27). Age bias plots revealed minimal inter-structure bias, apart from a higher average thorn age reading of 0.76 years from age classes 5–11 years for reader 1. Minor inter-reader bias was evident for vertebrae only; averaging 0.90 years higher for reader 1 from age classes 11 to 15 years. Preliminary evidence suggests caudal thorns could prove an effective non-invasive ageing tool for thorny skates.     

Revision of the bathyal cusk-eels of the genus Bassogigas (Ophidiidae) with description of a new species from off Guam, west Pacific Ocean

The bathyal genus Bassogigas (Teleostei: Ophidiidae) is revised based on 25 specimens, 18 from the west Atlantic Ocean and seven from the Indo-west Pacific Ocean. One specimen, from off Guam, west Pacific Ocean, represents a new species, Walker's cusk eel Bassogigas walkeri. The other 24 specimens all belong to the type species, Gills cusk eel Bassogigas gillii. A comparison between the Atlantic and the Indo-west Pacific Ocean specimens of B. gillii showed no differences in meristic and morphometric characters, but in two of the Indo-west Pacific Ocean specimens the sagittal otolith varied somewhat from the remaining specimens. The two Bassogigas species differ in the length of the lateral line, the number of scales in the midline of the body, the form of the median basibranchial tooth patches and in the thickness of the otolith.