Feeding strategy and cannibalism of the Argentine hake Merluccius hubbsi

The diet composition and feeding strategy of the Argentine hake Merluccius hubbsi in the San Matías Gulf were analysed in order to use this information for the sustainable management of the fishery. Merluccius hubbsi behaved as an opportunistic predator. Small M. hubbsi consumed planktonic crustaceans, whereas medium and large fish ate numerous prey taxa with low frequency of occurrence and variable specific abundance. Intra- and intercohort cannibalism were detected in all size groups and were particularly significant in large M. hubbsi. Medium-sized M. hubbsi consumed small conspecifics and large-sized M. hubbsi consumed both small and medium M. hubbsi. These results indicate that the removal of large M. hubbsi by fishing may increase the risk of overfishing by two combined effects: a direct effect of recruitment-overfishing and an indirect effect of growth-overfishing through an enhanced cannibalism of medium M. hubbsi on small M. hubbsi. Intra- and intercohort cannibalism and other trophic relationships in the M. hubbsi should therefore be considered explicitly in stock assessment models.     

Population structure,relative growth and morphological sexual maturity of the snapping shrimp Alpheus brasileiro Anker, 2012 (Caridea: Alpheidae) from the south-eastern coast of Brazil

The present study investigated the population structure of the snapping shrimp Alpheus brasileiro. We tested the hypotheses that the sex ratio of the population differs from the expected 1:1 and that the growth pattern differs between adults and juveniles and between sexes. Reproductive period, juvenile recruitment and morphological sexual maturity were estimated. Samples were collected in two periods. The first sampling occurred bimonthly from March 2013 to January 2014. The second sampling occurred monthly from April 2015 to March 2016. The population structure was determined based on the size-frequency distribution of different demographic categories. To analyse the relative growth, we measured the second pleuron length, major cheliped propodus length, major cheliped propodus width, major cheliped propodus height, appendix interna length, appendix masculina length. The results showed that the sex ratio did not differ from 1:1 (male:female). Reproduction and juvenile recruitment were continuous throughout the study period. The analysis of relative growth confirmed the hypothesis that males and females, and juveniles and adults, have different growth patterns, indicating distinct strategies of energy allocation. The estimated carapace length at the onset of morphological sexual maturity was 4.9?mm in males and 4.7?mm in females. The results obtained in this study are probably related to the monogamous social behaviour of A. brasileiro. Monogamy can influence demographic parameters such as sex ratio and the size at which males and females reach morphological sexual maturity.     

Using citizen science to obtain data on large,floating gelatinous spheres from NE Atlantic,attributed to egg mass of ommastrephid squid (Oegopsida,Cephalopoda, Mollusca)

A total of 27 large, gelatinous spherical masses observed in coastal Norwegian waters from Nordland to Aust-Agder Counties in Norway, and off Lysekil in Sweden, Muljica Island in Croatia, Gulf of Naples in Italy, Reqqa Point in Malta, and Saint Mandrier in France, during the months of April to September 2001 to 2017, are reported. Individual spheres measured 0.3–2 m in diameter, averaging one metre (n?=?24, ±0.53 m), with all but four sighted in suspension in the water column between 0.5 and 52 m depth, in water temperatures ranging between 10–21°C. About half of all spheres contained a yellow-red streak through their gelatinous core. Tissue samples were not obtained. We attribute these gelatinous spheres to the egg masses of squid (Cephalopoda, Oegopsida), and most likely to the ommastrephid Todarodes sagittatus, given similarities with egg masses of T. pacificus.     

Age and growth differences in two populations of the edible marine gastropod Buccinanops globulosus

Buccinanops globulosus is an edible marine gastropod that is being captured by artisanal fishermen without management regulations. As basic knowledge on population features is required in case a sustained commercial exploitation of this species is established, we estimated and compared the age and growth of B. globulosus in two populations separated by 16?km, inhabiting similar physical environments but different anthropic influence. Our results, based on stable oxygen isotope analysis and best fitted models by likelihood ratio tests, detected differences in age and growth between both samplings. Maximum shell marks suggest one year difference between populations. Richards was chosen as the best fitting model for both sampling sites and significant differences were observed between them. Human activities could be causing the age reduction among other irreversible effects on the population under anthropic influence. This should be considered when developing sustainable management regulations for this fishery resource, especially those based on shell/age size.     

Enzymatic polymorphisms in the Argentinian hake, Merluccius hubbsi Marini, of the Argentinian continental shelf

A survey described genetically encoded enzyme variation in 197 adult Argentinian hake, Merhccius hubhsi , collected from 10 sample sites on the Argentinian continental shelf. Four of 11 muscle enzyme loci were polymorphic ( PCM *, G3PDH *, EST-1 * and EST-2 *). Genotypes showed no significant difference between males and females. Only one of 37 tests of departure from Hardy-Weinberg equilibrium showed a significant difference. The allele frequency data were tested for genetic heterogeneity among locations. The overall significance of the total samples and among those from Patagonia Central was primarily due to heterogeneity at the EST-1 * locus. The implications of these findings in a population structure context are discussed.     

Development of the digestive system of Argentine hake,Merluccius hubbsi,larvae

The Argentine hake Merluccius hubbsi is an important fishery resource of the Southwestern Atlantic Ocean and it is also a potential species for cultivation. In this work, the digestive system development in field-caught hake larvae was studied using histological and histochemical approaches. The digestive tract of larvae was divided into: oropharyngeal cavity (OPC), esophagus, stomach (that develops in the preflexion stage), and intestine. The annexed digestive glands consisted of the liver and the exocrine pancreas. At the beginning of the preflexion stage, teeth were developed in the OPC. There were mucous cells in the esophagus secreting different glycoconjugates from hatching. The enterocytes in the posterior intestine exhibited supranuclear vesicles associated with protein absorption. Mucous cells were observed in the posterior intestine in the preflexion stage and, in the anterior region, ending the flexion stage. Each type of glycoconjugates has a specific role. Acidic mucins lubricate and protect from mechanical damage, sialomucines protect from bacterial infections and neutral mucins regulate the acidity of mucus secretion, protect against abrasion and participate in the formation of the chyme, indicating a pregastric digestion. The liver was present since hatching with pancreatic tissue inside and increased in size acquiring the typical structure with hepatocyte cords, sinusoids, vacuoles, and hepatic duct. The hepatocytes vacuolization increased with larval development. The pancreas became extra-hepatic, with basophilic acinar cells and acidophilic zymogen granules. Throughout the ontogeny, the increased structural and functional complexity of the digestive system reflected the transition to exogenous feeding and nutritional increasing needs.     

Mysid shrimp dynamics in relation to abiotic and biotic factors in the coastal lagoons of Maryland,Mid-West Atlantic,USA

The distribution and densities of two mysid species, Neomysis americana and Americamysis bahia in the coastal lagoons of Maryland were investigated using data collected monthly from March 2012 to December 2013. Mysid density was higher in the northern than southern bays in 2013 for Americamysis (P?=?0.043) and Neomysis (P?=?0.004). Neomysis americana density was inversely correlated with temperature (P?Neomysis densities (nos. m^?2?±?S.E) were negatively related to the catch-per-unit effort (CPUE?±?S.E) of fish predators (r?=??0.40, ?0.81; P?=?0.051, 0.002, respectively). Mysid density was higher in winter (March, 1.3?±?0.8 and spring, May, 1.4?±?1.3) 2012, when the CPUE of bay anchovy (Anchoa mitchilli) was relatively low (April: 5.8?±?2.3; and May: 11.9?±?4.5, 2012), than during summer (August, 0.003?±?0.002 nos. m^?2), when fish CPUE was relatively high (191.7?±?66.5). The observed seasonal patterns of mysid and fish densities, supported by the fact that mysids comprise 53–97% by weight of the diet of some of the abundant fish species in the bays, suggests a top-down control of mysids by fish predation. However, summer high temperatures in the bays exceeded 22°C, at which juveniles of N. americana have been reported to suffer high mortality, and perhaps contributed to the lower density of mysids in the summer.     

Seasonal variations in biochemical and physicochemical properties of actomyosin and energy content of the liver, gonads and muscle of mature Argentine hake, Merluccius hubbsi Marini

Seasonal variations in energy content of liver. gonads and muscle, and the condition factor (K) of mature hake, were investigated. High energy content values were found in the liver after spawning and during thegonadal restingperiod. Lowenergycontent valuesin liverand highenergycontent values in gonads were observed during the gonadal growth period. In some periods of the reproductive cycle, low values of energy content of muscle were found.
The condition factor profile was similar to the energy content profile of liver and muscle. Physicochemical and biochemical properties of actomyosin were monitored by reduced viscosity and Mg²⁺-ATPase activity. The profiles of these properties were similar to that of the condition factor.     

Changes in lipids and biochemical properties of actomyosin from pre- and post-spawned hake (Merluccius hubbsi Marini)

The total lipid contents of muscle, the liver somatic index and the total lipid contents of actomyosin in hakes changed with the gonadal condition of the fish. Non-polar lipids in actomyosin from pre-spawned hake were 145% higher than in actomyosin from post-spawned hake; polar lipids were 30% higher. The relative percentage of phospholipids changed from 32% in pre-spawned hake to 48% in post-spawned hake. The Mg²⁺-ATPase activity in actomyosin increased from the pre-spawned to the post-spawned conditions, and this could be related to a higher phospholipids to neutral lipids ratio in post-spawned hake. Gradual decreases in both Ca²⁺-ATPase activity and myosin: actin ratio during the gonadal development of fish were found, suggesting a partial loss of myosin functionality of the actomyosin complex.     

Acid phosphatase activity in pre- and post-spawning hake (Merluccius hubbsi)

1. The specific activity of muscle acid phosphatase (E.C. 3.1.3.1.) in pre- and post-spawning hake was investigated. 2. Specific activity values, 0.54 in pre-spawning hakes and 1.64 in post-spawning fish, have been obtained. 3. Using a histochemical test, acid phosphatase has been localized mainly in the connective tissue. The strongest reaction has been observed in post-spawning hake. 4. The increase of the lysosomal activity in the connective tissue may be related to the changes found in the muscle texture associated with spawning.     

Sexual differences in the increase of white muscle fibres in Argentine hake, Merluccius hubbsi, from the San Matias Gulf (Argentina)

Growth dynamics of white fibres from axial muscle has been investigated in Argentine hake, Merluccius hubbsi , discriminating between sexes for the first time. The frequency distributions of fibre diameters are remarkably different in both sexes at sizes between 42 and 63·9 cm total length (T.l.). Males have a much lower proportion of newly recruited fibres (0–10 μm) than females; at 52–53·9 cm T.l., females have 4% of fibres in that category and males 0·5%. It appears that, from this size interval onwards, the increase in muscle mass is due only to the increase in diameter of individual fibres, which may exceed 300 μm. The lower recruitment rate of new fibres in males, and its relationship to lower growth rates and smaller final sizes, are discussed, and possible effects of reproductive activity are considered.     

Feeding strategy of juvenile (age‐0+ year) Argentine hake Merluccius hubbsi in the Patagonian nursery ground

Age‐0+ year juvenile Argentine hake Merluccius hubbsi (60–150 mm total length, L_T) from San Jorge Gulf, north Patagonian shelf region of the Argentine Sea, had an almost exclusively pelagic diet dominated by the hyperiid amphipod Themisto gaudichaudii and the euphausiid Euphausia lucens. This suggested that final settlement and permanent demersal habitat utilization might not, as previously reported, occur at earlier sizes (c. 20 mm L_T). Their feeding strategy involves specialization at a population level towards both the main pelagic prey, indicating a narrow trophic niche. Novel data are provided which contribute to the growing body of information in relation to the age‐0+ year transitional stage in demersal fishes and particularly to M. hubbsi recruitment in the Argentine Sea.     

Growth pattern of the young of the year Argentine hake <Emphasis Type="Italic">Merluccius hubbsi</Emphasis> Marini, 1933 (Gadiformes Merluccidae) along the Brazilian and Uruguayan coasts

Morphology and morphometry of the sagittae otolith were studied in young of the year Argentine hake, Merluccius hubbsi in the Southeastern Atlantic. Geographical variation in the growth pattern of the young of the year Merluccius hubbsi was correlated with the differences found in otolith morphometry, relative growth, ring positions, as well as the formation of a new ring. The otolith development of M. hubbsi throughout its area of distribution accompanies an increasing northward temperature gradient, resulting in bigger otoliths and greater variability of ring position from northern to southern area. The canonical discriminate analysis showed that the otolith length and height explained most of the variation of the first discriminant function. We found significant differences in the discriminant scores between those samples from northern and southern area. As regards the Uruguayan coast and Southern Brazil, age groups zero shared some similarity as well as differences in growth; environmental features explain these differences but their effect on the adult fishes growth is still unknown.     

XX/XY sex chromosome system and chromosome markers in the snake eel Ophisurus serpens (Anguilliformes: Ophichtidae)

We report evidence of an XX/XY sex chromosome system in the snake eel Ophisurus serpens (Anguilliformes: Ophichthidae). We characterized the male and female karyotypes by C-, replication- and HaeIII-bandings. The 45S and 5S ribosomal gene families were located using dual fluorescence in situ hybridization, which showed that the 5S rDNA sites were present on the X chromosome, beside an autosome pair. FISH with a telomeric peptide nucleic acid probe enabled recognition of Interstitial Telomeric Sequences (ITSs), likely remnants of chromosomal rearrangements, in five chromosome pairs, including the rDNA-bearing ones. Possible mechanisms of the origin of sex chromosomes in this species are discussed, considering the presence of a sex-linked marker and ITSs.     

SSU rDNA analysis of Kudoa rosenbuschi (Myxosporea) from the Argentinean hake Merluccius hubbsi

The cloning and sequencing of the small subunit (SSU) ribosomal DNA gene from Kudoa rosenbuschi (myxosporean species associated with post-mortem myoliquefaction process in the Argentinean hake Merluccius hubbsi) is reported. The SSU rDNA was found to contain 1740 bp with a single polymorphic site with either a C or T at position 221. The sequence data obtained in this study and those known sequences of Kudoa species deposited in the GenBank were all analyzed to construct a phylogenetic tree. Nucleotide sequences showed the highest degree of identity with K. funduli, followed by K. miniauriculata, K. clupeidae and K. dianae. Phylogenetic analysis placed K. rosenbuschi in the same branch of K. clupeidae and K. funduli, and showed it to be closely related to K. dianae, K. paniformis and K. miniauriculata.     

Alien barnacle Amphibalanus amphitrite epizoic on two native oyster species in the southern Gulf of Mexico: spatio-temporal variability and current status of its epibiosis

The study examines the current invasive status of the barnacle Amphibalanus amphitrite on natural populations of two native oyster species (the eastern oyster Crassostrea virginica and the mangrove oyster C. rhizophorae) in a estuary of the southern Gulf of Mexico. The spatio-temporal variability of the frequency of occurrence, density and coverage of A. amphitrite on shells of each oyster species was examined and compared with those of other native congeners (A. eburneus, A. venustus and A. improvisus) with which it coexists. These three variables were significantly higher in C. rhizophorae than in C. virginica and were within the range recorded for its congeners. The density of this invasive barnacle varied significantly at spatial and temporal scales. Its highest overall mean density occurred in February (at temperatures 26–27°C and salinities 29–32). Multivariate analyses showed a separation of Amphibalanus assemblages into three main groups according to variations in their composition and abundance among sampling sites and dates. It was also determined that salinity and sedimentation rate were the variables that best explain the distribution of the Amphibalanus species within the estuary. The limited presence of A. amphitrite on C. virginica reefs is likely due to (amongst other factors) the relatively higher sedimentation loads (370–5709?g?m^?2?d^?1) and lower salinities (9–23) recorded in these sites. This study can act as a reference point for the subsequent monitoring of this invasive species, since possible increases in its population density and competitive ability could threaten the integrity of oyster populations and other organisms in the southern Gulf of Mexico.     

Notes on the biology of the Patagonian hake, Merluccius hubbsi (Marini), the southern blue whiting, Micromesistius australis (Norman) and others in the Falkland Islands shelf area

From the examination of samples of fish caught in two commercial surveys on trawling grounds around the Falkland Islands, it is noted that Patagonian hake, Merluccius hubbsi , southern blue whiting, Micromesistius australis , and others occurred in fishable quantities especially to the east of Beauchêne Islands where fishes were larger and more numerous. However 47% of the total catch consisted of southern blue whiting which was 100% infested by a myxosporidian parasite in its musculature rendering it unsuitable for human consumption.     

Hypo-osmotic shock and the role of freshwater input on the post-bloom recovery of Cyanothece sp. in Lake St Lucia,South Africa

Modern anthropogenic modifications to aquatic environments, specifically hydrodynamic alterations, play a major role in cyanobacterial bloom potential. In shallow-water ecosystems, salinity is a driver of microbial communities and increases in salinity may facilitate the bloom potential of competitive cyanobacteria. This study investigated the osmotic response and mortality rate of a persistent bloom-forming (18 months) cyanobacterium, Cyanothece sp., isolated from Lake St Lucia (South Africa), after sudden hypo-osmotic shock. Laboratory experiments were performed with Cyanothece sp. cells to observe osmotic responses and to determine mortalities during salinity reductions. In general, Cyanothece sp. cells conformed to the external medium at all salinity levels used in the treatments, reducing their intracellular osmolality in response to salinity downshifts. There were limits to this, however, as successful downshift was not observed during the freshwater exposure treatment. Highest mortality rates occurred in cultures that were grown at high salinities (i.e. 180, 240 and 300 units), as well as in treatments with large salinity downshifts (e.g. 120 salinity unit reduction and direct freshwater exposure). Cyanothece sp. has been shown to sustain bloom status for long periods. Its ability to tolerate high salinities and respond to sudden salinity downshifts is an important factor in its bloom success. However, it is still susceptible to reductions in salinity that may occur due to heavy rainfall and floods, which highlights the importance that freshwater plays in the bloom ecology of a persistent bloom-forming halotolerant cyanobacterium, as freshwater inputs markedly influence the physiology of the cells and their survival ability.     

Morphological and biochemical approaches to assess the nutritional condition of the Argentine hake Merluccius hubbsi larvae from two different nursery areas

The Argentine hake, Merluccius hubbsi, is one of the most important fishing species in the Argentine Sea due to its great abundance and high-quality meat. The study of the nutritional condition is widely used to determine the physiological state of the fish larvae and to estimate their survival possibilities. The larval nutritional condition reflects the environmental conditions to which they have been exposed and represents a useful instrument to determine favourable nursery areas. It also provides tools for the comprehensive management of a population subjected to fishing exploitation. This study aimed to determine potential differences in the nutritional condition of M. hubbsi larvae from the two fishing stocks (Northern and Southern) of the species. The authors assessed the nutritional condition of larvae captured during the 2012 main reproductive peak in the nursery areas of each population. Two different methodologies were applied: a morphometrical approach, by recording five morphometric variables, and a biochemical technique, employing the RNA/DNA index (RD_s) and its derived index of growth performance. The morphometrical indexes did not show differences in the larval condition between both stocks. Nonetheless, the RD_s index did detect differences in the nutritional condition of larvae from different stocks. The RD_s index of larvae in pre-flexion and flexion stages showed significant differences between stocks, indicating that these stages are more susceptible to starvation. The results suggest that the biochemical indexes prove to be more sensitive than the morphometric indexes to detect slight differences in hake larvae nutritional condition. The scope and limitations of these techniques for the analysis of the nutritional condition of larvae are discussed.     

Density-dependent growth and sexual maturity of silver hake in the north-west Atlantic

Stock abundance was the most important predictor of sexual maturation of age 2 and 3 silver hake in the north-west Atlantic between 1973–1990. Growth at ages 1 and 2 in the southern stock was significantly and negatively correlated with stock abundance (r²>0.56, P <0.01). Sexual maturity may be mediated through competition and growth during the first and second years of life. In the northern stock, growth and stock abundance was not significantly correlated ( P >0.05). Here, increased sexual maturity at ages 2 and 3 during 1973–1990 may have occurred without increased somatic growth, already near its maximum, due to the relatively cooler water temperatures of the Gulf of Maine. Logistic regression models indicated that maturation is dependent on age, stock density and an age-density interaction.