Fishery and Ontogenetic Driven Changes in the Diet of the Spiny Dogfish, Squalus acanthias, in Patagonian Waters, Argentina

The diet of the spiny dogfish in northern and central Patagonian waters was studied from the by-catch of the bottom trawling fisheries directed to Argentine hake Merluccius hubbsi and Argentine red shrimp Pleoticus muelleri between 1996 and 1998. Food habits were analyzed in relation to sex and maturity of sharks. Also, the relationship between diet and abundance of the main prey was explored. Intraspecific diet comparisons were performed. Differences in diet were found between immature individuals, mature males, and mature females. The Argentine shortfin squid Illex argentinus, the Argentine hake and ctenophores Pleurobrachia pileus were the most important prey for the spiny dogfish. Immature and small individuals were pelagic predators. After sexual maturity, the spiny dogfish shifted its diet. Mature and large individuals tended to reduce the consumption of ctenophores, and increase the consumption of demersal and benthic species. Previous diet studies on the spiny dogfish in 1984–1985 and 1994 indicated that the Argentine hake was the most important prey. In the present study, carried out in 1998, squid was the most important prey, followed by the hake. This diet change was related to the major decrease of hake due to overfishing and the increase of squid abundance between 1994 and 1999.     

Global population structure of the spiny dogfish Squalus acanthias,a temperate shark with an antitropical distribution

The spiny dogfish (Squalus acanthias) is a temperate, coastal squaloid shark with an antitropical distribution in the Atlantic and Pacific oceans. The global population structure of this species is poorly understood, although individuals are known to undergo extensive migrations within coastal waters and across ocean basins. In this study, an analysis of the global population structure of the spiny dogfish was conducted using eight polymorphic nuclear microsatellite markers and a 566‐bp fragment of the mitochondrial ND2 gene region. A low level of genetic divergence was found among collections from the Atlantic and South Pacific basins, whereas a high level of genetic divergence was found among Pacific Ocean collections. Two genetically distinct groups were recovered by both marker classes: one exclusive to North Pacific collections, and one including collections from the South Pacific and Atlantic locations. The strong genetic break across the equatorial Pacific coincides with major regional differences in the life‐history characters of spiny dogfish, suggesting that spiny dogfish in areas on either side of the Pacific equator have been evolving independently for a considerable time. Phylogeographic analyses indicate that spiny dogfish populations had a Pacific origin, and that the North Atlantic was colonized as a result of a recent range expansion from the South American coast. Finally, the available data strongly argue for the taxonomic separation of the North Pacific spiny dogfish from S. acanthias and a re‐evaluation of the specific status of S. acanthias is warranted.     

Bombesin-like immunoreactive material in the gut, and the effect of bombesin on the stomach circulatory system of an elasmobranch fish, Squalus acanthias

The distribution, nature and amount of bombesin-like immunoreactivity (IR) in the gastrointestinal canal and its afferent vessels was investigated in the spiny dogfish (Squalus acanthias) together with the in vitro effect of synthetic bombesin on perfusion flow through the vascularly perfused dogfish stomach. Nerve fibres showing bombesin-like IR frequently occurred in the walls of the anterior mesenteric and coeliac arteries and the intrinsic vessels of the gut. Chromatographic studies revealed that multiple peaks of bombesin-like IR material were present in extracts of the spiny dogfish gastrointestinal vessels. Bombesin-like IR was also present in muscle and mucosal layers of the gut with higher levels in muscle compared with mucosa, and higher levels in the stomach than in the intestine and the rectum. Exogenous bombesin increased the flow through the vasculary perfused spiny dogfish stomach in a dose-dependent manner. Studies with tetrodotoxin and atropine showed that bombesin probably exerts its effect directly on the vascular musculature. It is concluded from this study that bombesin-like material is present in nerves innervating the gut circulatory system of the spiny dogfish. Bombesin may affect the blood-flow to the gastrointestinal canal, possibly via a direct effect on vascular smooth muscle.     

Reproductive Biology of the Smooth Dogfish, Mustelus canis, in the Northwest Atlantic Ocean

Shark populations tend to be highly vulnerable to overexploitation due to low fecundity and slow growth rates. Recent fishing pressure on the smooth dogfish in the northwest Atlantic has created a necessity for more information about their basic biology. Length and age at maturity, fecundity, and reproductive season were estimated. Total length at 50% maturity was 102cm for females, and 86cm for males. The majority of females were mature at age 4 or 5, and all males were mature at 2 or 3 years of age. Females had an 11–12 month gestation with parturition occurring in May, ovulation occurring between May and July likely in late May and early June, and mating occurring between May and September. Fecundity ranged between 3 and 18 pups per litter, and was positively related to length and age, with a mean of 9.53 pups per litter. Sperm was found in the terminal zone of the oviducal gland of females throughout the year.     

Spatial overlap of shark nursery areas and the salmon farming industry influences the trophic ecology of Squalus acanthias on the southern coast of Chile

Potential interactions between marine predators and humans arise in the southern coast of Chile where predator feeding and reproduction sites overlap with fisheries and aquaculture. Here, we assess the potential effects of intensive salmon aquaculture on food habits, growth, and reproduction of a common predator, the spiny dogfish—identified as Squalus acanthias via genetic barcoding. A total of 102 (89 females and 13 males) individuals were collected during winter and summer of 2013–2014 from the Chiloé Sea where salmon aquaculture activities are concentrated. The low frequency of males in our study suggests spatial segregation of sex, while immature and mature females spatially overlapped in both seasons. Female spiny dogfish showed a functional specialist behavior as indicated by the small number of prey items and the relative high importance of the austral hake and salmon pellets in the diet. Immature sharks fed more on pellets and anchovies than the larger hake‐preferring mature females. Our results also indicate that spiny dogfish switch prey (anchovy to hake) to take advantage of seasonal changes in prey availability. Despite differences in the trophic patterns of S. acanthias due to the spatial association with intensive salmon farming, in this region, there appears to be no difference in fecundity or size at maturity compared to other populations. Although no demographic effects were detected, we suggest that a range of additional factors should be considered before concluding that intensive aquaculture does not have any impact on these marine predators.     

Age and growth of spiny dogfish <Emphasis Type="Italic">Squalus acanthias</Emphasis> (Squalidae,Chondrichthyes) in pacific waters off the Kuril Islands

On the basis of materials collected from catches of drift salmon nets in Pacific waters off the Kuril Islands from 2005 to 2006, the age and rate of growth of spiny dogfish Squalus acanthias are considered. Individuals with a length of 67–123 cm and weight of 1140–5970 g aged 10–26 years were represented in catches. In almost all age classes, the length of males was greater and the weight smaller than in females. The lifespan of females is slightly higher as compared to males-26 and 25 years, respectively. The values of K coefficient of the Bertallanffi equation of growth in males and females comprised 0.10 and 0.05 and the calculated values of the asymptotic body length comprised 116.3 cm and 147.2 cm. A relationship was found between the age of spiny dogfish and the spine size: its length (r _s = 0.693), base width (r _s = 0.815), and base length (r _s = 0.823).     

Reproductive and population parameters of spiny dogfish Squalus acanthias in the south‐western Atlantic Ocean

The objective of this study was to estimate reproductive and population parameters of the spiny dogfish Squalus acanthias for the south‐western Atlantic Ocean. In total, 2714 specimens (1616 males and 1098 females) were collected from surveys carried out using research vessels. Males ranged from 225 to 861 mm total length (L_T) and females from 235 to 925 mm L_T. The size at maturity of females (651 mm) was significantly greater than that of males (565 mm). The maximum proportion of mature individuals (P_max) of the gestation ogive was <1, which indicates that a proportion of mature females was not in gestation. This inactivity may be explained by the occurrence of resting periods between cycles or by the asynchrony of the reproductive cycle. The estimated P_max for the maternity ogive suggested that about one third of mature females were in the maternity stage (i.e. with embryos >156 mm). The temporal and spatial co‐occurrence of non‐gravid adult females at different stages of ovarian development, as well as gravid females at all embryonic development stages would indicate that the female reproductive cycle in the south‐western Atlantic Ocean is asynchronous. The results indicate that S. acanthias is susceptible to fishing pressure on account of its length at maturity, extended reproductive cycles and low fecundity.     

Diet of spiny dogfish, Squalus acanthias Linnaeus, on the east coast, South Island, New Zealand

Stomach content data from 7283 spiny dogfish, Squalus ucunthius Linnaeus, from east coast South Island of New Zealand are presented. The major dietary components based on occurrence were 60% crustaceans and 15% fish. The principal food items were the post-larval phase of the squat lobster, Munida greguria Fabricius (30%), and the euphausiid, Nyctiphanes australis Sars (20%). Commercial fish species contributed to less than 5% of the diet. Diet of dogfish varied with dogfish size and sex. Compared to northern hemisphere studies, spiny dogfish in this study area had (1) a high proportion of crustaceans in their diet, (2) a relatively low percentage of empty stomachs, (3) a relatively high incidence of cannibalism.     

Reproductive cycle,sexual maturity and longevity of Odontophrynus americanus (Anura: Odontophrynidae) in South Brazil

Studies on the reproductive biology and age of amphibians provide primary information about the life history and population demographic parameters of species. Here, we describe the reproductive cycle, size–fecundity relationships, reproductive effort, sexual dimorphism and sexual maturity of Odontophrynus americanus, the flood frog, from South Brazil. A total of 96 individuals were analysed. The reproductive cycles of males and females were described through morphoanatomical analysis of testis and ovary. Age at onset of sexual maturity and estimated longevity were determined by skeletochronology. Individuals of O. americanus presented a potentially continuous reproductive cycle with a peak of reproductive activity in the warmer months. Females presented a higher reproductive investment than males. Sexual maturity was reached at around one year of age for both sexes while longevity differed between the sexes, with females living up to six years and males up to ten years. No evidence of sexual size dimorphism was found. This study is among the few that have assessed age at sexual maturity and longevity in a Neotropical anuran. Basic aspects of life history are of paramount importance because they allow comparisons and test of hypotheses to be made, which can help to build generalizations about the evolutionary meaning of ecological strategies.     

Using the composite variables of reproductive morphology, histology and steroid hormones to determine age and size at sexual maturity for the thorny skate Amblyraja radiata in the western Gulf of Maine

Age at size was linked to sexual maturity in 77 male and 93 female thorny skates Amblyraja radiata from the western Gulf of Maine using three criteria: 1) gross reproductive morphology, 2) histology and 3) steroid hormone concentrations. Age-bias plots and the coefficient of variation from vertebral band counts suggested that the ageing method represented a non-biased and precise approach to the age assessment of A. radiata . Maturity ogives for males, based on data gathered for clasper length, circulating testosterone concentrations and proportion of mature spermatocysts within the testes, predicted that 50% maturity occurred at a total length ( L _T) of 865 mm and c. 10·90 years of age. For females, maturity ogives, based on data gathered for ovary mass, shell gland mass, follicle size and circulating oestradiol concentrations, predicted that 50% maturity occurred at 875 mm L _T and c. 11·00 years of age. Collectively, the results suggest that analysis of several contemporaneous reproductive variables offers an accurate determination of sexual maturity in the thorny skate.     

Bomb dating and age validation using the spines of spiny dogfish (Squalus acanthias)

Bomb radiocarbon has previously been used to validate the age of large pelagic sharks based on incorporation into vertebrae. However, not all sharks produce interpretable vertebral growth bands. Here we report the first application of bomb radiocarbon as an age validation method based on date-specific incorporation into spine enamel. Our results indicate that the dorsal spines of spiny dogfish, Squalus acanthias, recorded and preserved a bomb radiocarbon pulse in growth bands formed during the 1960s with a timing which was very similar to that of marine carbonates. Using radiocarbon assays of spine growth bands known to have formed in the 1960s and 1970s as a dated marker, we confirm the validity of spine enamel growth band counts as accurate annual age indicators to an age of at least 45 year. Radiocarbon incorporation into northeast Atlantic dogfish spines occurred in similar years as those in the northwest Atlantic and northeast Pacific, although the amount of radiocarbon differed in keeping with the radiocarbon content of the different water masses. Published reports suggesting that Pacific dogfish are longer lived and slower growing than their Atlantic counterparts appear to be correct, and are not due to errors in interpreting the spine growth bands. Radiocarbon assays of fin spine enamel appears to be well suited to the age validation of sharks with fin spines which inhabit the upper 200 m of the ocean.     

Characterization and isolation of DNA microsatellite primers in the spiny dogfish (Squalus acanthias)

The North Atlantic spiny dogfish (Squalus acanthias) population has been declining since the 1980s. Proper management of this population is essential as dogfish are prone to rapid collapse based on the unique biology of this species. We characterized eight microsatellite loci for spiny dogfish to use in determining the genetic structure of this species along the Atlantic coast of the USA.     

Bilirubin metabolism in the spiny dogfish, Squalus acanthias, and the small skate, Raja erinacea.

1. The main bilirubin conjugate in bile of spiny dogfish (Squalus Acanthias) and small skate (Raja Erinacea) is bilirubin monoglucuronide. 2. Microsomal preparations from dogfish and small skate liver have similar bilirubin UDPglucuronyltransferase (UDPGT) activity and catalyze the conjugation of bilirubin with glucose from UDPglucose. 3. The activity of bilirubin glucosidation (UDPGT) was 0.5 times UDPG1T activity in dogfish and 0.15 times in skate liver microsomes. 4. Sodium cholate increased UDPGT and UDPG1T activities in dogfish and skate liver microsomal preparations only minimally, but the detergent markedly increased thermolability of UDPGT in skate liver microsomes.     

Variations in age and size at maturity of female Nile tilapia, Oreochromis niloticus, populations from man-made lakes of Côte d'Ivoire

The reproductive characteristics of Oreochromis niloticus females were studied in two large hydroelectric dams and 6 small agropastoral reservoirs of Côte d'Ivoire, selected for their diversity of environmental conditions and sizes (6 to 80000 ha). Comparative analysis of age and size at maturity revealed large differences between the populations with early maturity, late maturity, and intermediate situations. All the populations matured in their first year, between 5.6 and 10 months. Age and size at maturity were positively correlated with the reservoir area. The range of variation in age at maturity between populations was far greater than that of size at maturity. However, size at maturity also appears to be very plastic as intra-population variations of 2 to 3 cm were found between consecutive years. A comparison of age at maturity for a population in 1994 and 1996 showed that this trait is also likely to vary significantly at the intra-population level. Environmental factors which could potentially affect age and size at maturity are discussed. Growth differences are the probable explanation for the observed patterns of variation between populations. Rapid changes in age and size at maturity at inter or intra-population levels suggest that the observed variations might be explained by differences in environmental variables (phenotypic plasticity) rather than by genetic differences.     

Reproductive biology and implications for management of the painted sweetlips Diagramma pictum in the southern Arabian Gulf

The reproductive biology of the painted sweetlips Diagramma pictum was determined from 487 individuals collected between January and December 2010 in the southern Arabian Gulf. There was no evidence of sex change and the combination of histological results with the sex composition of the size and age structures indicated a gonochoristic sexual pattern. There were peaks in gonado-somatic indices for females in March and October with spawning occurring during two seasons (April to May and November). The mean size and age at sexual maturity (L(m50) and A(m50) ) were 35·7 cm fork length (L(F) ) and 2·9 years for females and 26·7 cm L(F) and 0·5 years for males. The maximum recorded age (11 years) and small mean size and young age at sexual maturity for males may be a direct result of intensive demersal fishing in the southern Arabian Gulf. There was an exponential increase in the cumulative reproductive potential with size and a linear increase with age for both sexes. The mean L(F) (L(c50) ) at which D. pictum became vulnerable to capture was 33·3 cm, which corresponded to only 3 and 7% of the cumulative reproductive potential of males and females, respectively. Size-specific and age-specific reproductive potential indicated that conventional regulations that equate the mean size at first capture to sexual maturation are unsuitable for the management of D. pictum.     

Cell and molecular biology of SAE, a cell line from the spiny dogfish shark, Squalus acanthias

Cartilaginous fish, primarily sharks, rays and skates (elasmobranchs), appeared 450 million years ago. They are the most primitive vertebrates, exhibiting jaws and teeth, adaptive immunity, a pressurized circulatory system, thymus, spleen, and a liver comparable to that of humans. The most used elasmobranch in biomedical research is the spiny dogfish shark, Squalus acanthias. Comparative genomic analysis of the dogfish shark, the little skate (Leucoraja erincea), and other elasmobranchs have yielded insights into conserved functional domains of genes associated with human liver function, multidrug resistance, cystic fibrosis, and other biomedically relevant processes. While genomic information from these animals is informative in an evolutionary framework, experimental verification of functions of genomic sequences depends heavily on cell culture approaches. We have derived the first multipassage, continuously proliferating cell line of a cartilaginous fish. The line was initiated from embryos of the spiny dogfish shark. The cells were maintained in a medium modified for fish species and supplemented with cell type-specific hormones, other proteins and sera, and plated on a collagen substrate. SAE cells have been cultured continuously for three years. These cells can be transfected by plasmids and have been cryopreserved. Expressed Sequence Tags generated from a normalized SAE cDNA library included a number of markers for cartilage and muscle, as well as proteins influencing tissue differentiation and development, suggesting that SAE cells may be of mesenchymal stem cell origin. Examination of SAE EST sequences also revealed a cartilaginous fish-specific repetitive sequence that may be evidence of an ancient mobile genetic element that most likely was introduced into the cartilaginous fish lineage after divergence from the lineage leading to teleosts.     

Further evidence for ancient role of ACTH peptides at melanocortin (MC) receptors; pharmacology of dogfish and lamprey peptides at dogfish MC receptors

The cloning of melanocortin (MC) receptors in distant species has provided us tools to get insight in how the ligand-receptors interactions in the MC system have evolved. We have however lacked studies on pharmacology of native ancient melanocortin peptides at the ancient MC receptors. In this paper we synthesized melanocortin peptides from both the sea lamprey (Petromyzon marinus) and spiny dogfish (Squalus acanthias) and tested them on the MC3 and MC4 receptors from spiny dogfish. The results show that both the dogfish and lamprey ACTH peptides have similar or higher affinity than the dogfish alpha-, beta- and gamma-MSH peptides to the dogfish MC3 and MC4 receptors. Moreover, both the dogfish and lamprey ACTH peptides have more than 10-fold higher affinity than alpha-MSH to the dogfish MC4 receptor. We also show that dogfish delta-MSH is able to bind to MC receptors and its potency is higher than of dogfish beta-MSH, which is considered to be its precursor. Our results provide the first evidence that native ACTH ligands from dogfish and lamprey have a preference above native MSH peptides to ancient version of the MC3 and MC4 receptors. This further strengthens the hypotheses that the ligand contributing to the first version of the melanocortin ligand-receptor system resembled ACTH.     

Phylogenetic Studies of Complete Mitochondrial DNA Molecules Place Cartilaginous Fishes Within the Tree of Bony Fishes

It is commonly acknowledged that cartilaginous fishes, Chondrichthyes, have a basal position among the Gnathostomata (jawed vertebrates). In order to explore this relationship we have sequenced the complete mitochondrial genome of the spiny dogfish, Squalus acanthias, and included it in a phylogenetic analysis together with a number of bony fishes and amniotes. The phylogenetic reconstructions placed the dogfish among the bony fishes. Thus, and contrary to the common view, the analyses have shown that the position of the sharks is not basal among the gnathostomes. The presently recognized phylogenetic position of the dogfish was identified irrespective of the outgroup used, echinoderms or agnathan fishes. The lungfish was the most basal gnathostome fish, while the teleosteans had an apical position in the piscine tree. A basal position of the dogfish among the gnathostomes was statistically rejected, but the phylogenetic relationship among the coelacanth, spiny dogfish, and teleosts was not conclusively resolved. The findings challenge the current theory that sharks and other chondrichthyans, if monophyletic, are the sister group to all other extant gnathostomes. The results open to question the status of several morphological characters commonly used in piscine phylogenetic reconstruction, most notably the presence versus absence of endochondral bone in the endoskeleton, the macromeric versus micromeric structure of the exoskeleton, and the presence/absence of swimbladder and/or lung. The study also confirmed recent findings demonstrating that the origin of the amniotes is deeper than the diversification of extant bony fishes. Received: 12 March 1998 / Accepted: 12 June 1998