Northeast Arctic Cod and Prey Match-Mismatch in a High-Latitude Spring-Bloom System

By combining an ocean model, a nutrient-phytoplankton-zooplankton-detritus-model and an individual-based model for early life stages of Northeast Arctic cod we systematically investigate food limitations and growth performance for individual cod larvae drifting along the Norwegian coast from spawning grounds toward nursery areas in the Barents Sea. We hypothesize that there is food shortage for larvae spawned early and late in the 2-monthlong spawning period, and to a larger degree to the north and south of the main spawning grounds in the Lofoten. Model results for three contrasting years (1995, 2001, and 2002) show that spawning early in the season at spawning grounds in the Lofoten and farther north is favorable for larval growth close to their size- and temperature-dependent potential. Still, both early and late spawned larvae experience slower growth than individuals originating closer to the time of peak spawning late March/early April. The reasons are low temperatures and shortage in suitable prey, respectively, and this occurs more frequent in areas of strong currents about 1–2 months post hatching. In particular, late spawned larvae grow relatively slow despite higher temperatures later in the season because they are outgrown by their preferred prey.

Assessment of physiological and biochemical indicators of the state of the so-iuy mullet Liza haematocheilus (Temminck & Shlegel, 1845) in the Azov-Black Sea Basin

A comprehensive analysis of the physiological state of the so-iuy mullet, inhabiting the Sea of Azov, has been carried out during its pre-spawning period in 2020–2021. The hematological characteristics of the investigated individuals have been evaluated. It has been revealed that the content of protein and lipids in fish tissues was at the level of average longterm values. The content of protein and lipids in the gonads of females was significantly higher than that of males, which is explained by the forthcoming stage of spawning. It has been determined that the contribution of albumin to the total blood serum protein was minimal, which could be a consequence of the low feeding rate of the fish. At the same time, no stress effect was identified-glucose was within its normal range.

Biochemical and hematological parameters of the roach Rutilus rutilus heckelii (Nordmann, 1840) from the Sea of Azov stock in the spring season of 2020–2021

This work presents the results of the investigation of the physiological state of the roach Rutilus rutilus heckelii breeders from the Sea of Azov stock during the spawning period. It has been established that, in the spring season of 2020 and 2021, the content of proteins and lipids in fish tissues, as well as hematological parameters in all investigated roach specimens from different water bodies were consistent with the average long-term values. The content of proteins in the muscles and liver of roach does not differ by sex. A higher protein content in the gonads of females is characteristic of the pre-spawning period due to the process of gonad maturation. The high content of lipids in the gonads of males apparently results from the lower energy consumption for maturation of the gonads and spawning. The average concentration of sodium and potassium ions decreased in comparison with the values obtained in 2020, while the concentration of chloride anions increased. It has been concluded that the physiological state of all investigated roach specimens was normal.

Chamelea gallina reproductive biology and Minimum Conservation Reference Size: implications for fishery management in the Adriatic Sea

Background The striped venus clam Chamelea gallina is an economically important species in Adriatic Sea fisheries. The use of hydraulic dredging for its catch has a long history in Italy and its management faced several stages of development in the last 40 years. A great effort has been made in the past two decades to move from poorly or weakly managed fisheries to a well-structured co-management system to improve the sustainability of this fishery. However, a prerequisite for appropriate resource management is a sound knowledge of the biology and reproductive strategy of the species. Results We investigated three major biological features– the gametogenic cycle, size at sexual maturity and partial fecundity – by microscopic, histological and video analysis techniques. We demonstrated that its breeding season is driven by rises in seawater temperature and chlorophyll-a concentration and that its spawning period lasted from March to September. Size at sexual maturity was reached very early in the life cycle. As regards partial fecundity – the number of mature oocytes potentially released by females with ripe gonads in a single release event – varied in relation to size. Nevertheless, the reduction on the Minimum Conservation Reference Size (MCRS) from 25 to 22 mm (Delegated Regulation (EU) 2020/2237) lead to a 40% reduction in the number of emitted eggs. Conclusions We suggest that the ability of Adriatic clam stocks to withstand the strong fishing pressure of the past 40 years and the present one is due to their high reproductive potential and multiple spawning events combined with the effect of management measures (closed areas/seasons, quota, MCRS) and technical constraints on the gear and the sieve on board. Moreover, since the reduced MCRS for Venus shells is still larger than the size at maturity, it will probably not be detrimental to the reproductive capacity of the stock.

First report on the diet and reproductive biology of red-toothed triggerfish Odonus niger (Ruppell, 1836) from the south-eastern Arabian Sea

The feeding habits and reproductive biology of red-toothed triggerfish Odonus niger (Ruppell, 1836) was analysed from 449 specimens collected from the Karnataka coast of the south-eastern Arabian Sea. Of the total stomachs examined, only 54 (12%) were empty and 395 contained food remains. The diet comprised crustacean remains (48.0%), zooplankton (21.4%), algae (16.5%), fish remains (6.1%) and cephalopod remains (5.3%) along with partially digested matter (2.3%) and detritus (0.4%). The species was found to be a generalist feeder and an omnivore. The overall sex ratio between males and females (1: 0.44) was significantly (P < 0.05) different. Histological examination of the ovaries indicated asynchronous ovarian development in females, with males maturing earlier than females. The gonadosomatic index (GSI) patterns of males and females, and the presence of ripe ovaries and spermatozoids suggested that April–May is the peak spawning period. The absolute and relative fecundity estimates ranged from 16,464–312,420 eggs and 251–2812 eggs g−1 respectively. Fecundity was positively correlated with total length and body weight. The biological information on diet composition and reproductive traits provided for the first time in this study can facilitate conservation, management and sustainable exploitation of this species in the study area.

Characteristics of biochemical indicators of sperm production of carp males while using naked oats in the nutrition process during pre-sprawning period

In the research there have been used males of the Nyvka intra-breed type of the Ukrainian scaly carp breed, which were kept during the pre-spawning period in the pond conditions of the State Enterprise “Experimental fish farm Nyvka” within the Institute of Fisheries of the National Academy of Agrarian Sciences of Ukraine (IFNAASU). The carps were divided into 3 groups. The first group (Experiment I) was fed 100 % naked oats, the second (Experiment II) – 30 %, the control group of fish (Control) was fed a grain mixture. The quality of sexual products of male carp was assessed by determining the effect of adding naked oats to their diet during the pre-spawning period. Indicators of sperm motility and fertilizing ability, content of γ-, β- and α-globulins, albumin, prealbumin, and physiological characteristics of ejaculates of respiratory and regenerative capacity, activity of enzymes of respiratory chain of mitochondria (CHO and SDG) were studied. Given the increased productivity of fish sperm, in particular the increase in the number of sperm with rectilinear motion, decrease in the number of inanimate sperm and changes in the protein formula of germ cells, it is advisable to add naked oats to the main diet in the amount of 30 %.

Sexual dimorphism patterns of the White Sea threespine stickleback (Gasterosteus aculeatus)

Sexual dimorphism (SD) in the threespine stickleback Gasterosteus aculeatus reflects the different roles of the sexes in reproduction and their adaptations to different ecological niches. We quantified SD in one population of marine stickleback from the White Sea, collected during the spawning period from three spawning grounds, each at a distance of 5 km or less from the others. We used a landmark-based approach to quantify variation in 44 morphometric linear traits. In total, 749 females and 693 males were analyzed. In males, anterior body parts are larger — the base of the caudal fin and armor structures such as the first and second dorsal spines and the pelvic spine. Females have larger posterior bodies — the abdomen, pelvic girdle and the third dorsal spine. The SD of caudal body parts exhibits complex patterns. In White Sea threespine stickleback, SD patterns are generally similar to other populations of the species, but more often show male-biased patterns. Female-biased size SD may be associated with the female biased sex ratio of White Sea stickleback.

Population Ecology Studies on Infaunal Polychaetes of Pauatahanui Inlet

<p>Macrofaunal polychaete densities across a stable, fine-sand, intertidal flat in Pauatahanui Inlet were examined from a set of seasonal samples, 500 micron sieve processed, from a stratified transect pair. Density Patterns had shore-normal trends, despite apparently weak tidal-cycle environmental gradients. Zones of high abundance of common species persisted unchanged, but seasonal increase and decline occurred within them, with also some population redistribution attributable to differential mortality/recruitment, or possibly to migration. Correlation analysis did not detect interspecies relationships linked to the abundance and zonation of the common polychaetes, all deposit-feeders. The population dynamics of six species was investigated from the transect-pair seasonal samples, supplemented by subsequent more finely-sieved samples during dense recruitment periods. The maldanid Axiothella serrata had three identifiable age groups O, I, and II+, with I plus II+ density to about 550 m-2. The new O group began to appear in October-November, as aggregates below 3 cm sediment depth, believed to represent lecithotropic, direct-developing, siblings from egg masses of the II+ group. Juvenile setiger-total frequencies indicated synchronous adult spawning occurred at varying intervals during an approximate six month period. Peak density of dispersed, near-surface recruits reached 29 thousand m-2. Setiger-total was the most sensitive indicator of size and age in juveniles of up to about 15 setigers. Zonation patterns were age specific. The predominantly lower-shore capitellid, Heteromastus filiformis had a short summer spawning period with settlement ending before May, when population density was up to 10 thousand m-2. Merger of O group into the adult size range occurred in about one year, and probably first spawning was at the end of the second year, with life span of three years or more. The nereidid Nicon aestuariensis had I+ and older age groups at barely detectable densities. Spawning was probably in late summer although an O group, at about 500 m-2, was not detected until May. The spionid Scolecolepides benhami had apparently unchanging size structure and density (about 400 m-2 transect-wide); new settlement was not detected. High density occurred only in a narrow near-shore strip. Nicon aestuariensis also declined down-shore, but more gradually. The spionid Microspio sp. and capitellid Capitella sp. were short-lived, near-surface species, with apparently continuous recruitment from planktotrophic and direct-development respectively. A spring recruitment increase created at first a separate modal group of juveniles, and raised Microspio sp. density to 45 thousand m-2 and Capitella sp. to 7 thousand m-2. Capitella sp. declined in density downshore, but Microspio sp. was only weakly zoned. The common polychaetes had largely concordant density cycles with settlement (or peak settlement) spring-summer orientated, although 500 micron mesh processing detected the peak of surviving adults in autumn-winter. Pauatahanui polychaetes as an assemblage, life history traits, links between population structure and zonation, and problems in polychaete population studies are discussed.</p>

Population Ecology Studies on Infaunal Polychaetes of Pauatahanui Inlet

<p>Macrofaunal polychaete densities across a stable, fine-sand, intertidal flat in Pauatahanui Inlet were examined from a set of seasonal samples, 500 micron sieve processed, from a stratified transect pair. Density Patterns had shore-normal trends, despite apparently weak tidal-cycle environmental gradients. Zones of high abundance of common species persisted unchanged, but seasonal increase and decline occurred within them, with also some population redistribution attributable to differential mortality/recruitment, or possibly to migration. Correlation analysis did not detect interspecies relationships linked to the abundance and zonation of the common polychaetes, all deposit-feeders. The population dynamics of six species was investigated from the transect-pair seasonal samples, supplemented by subsequent more finely-sieved samples during dense recruitment periods. The maldanid Axiothella serrata had three identifiable age groups O, I, and II+, with I plus II+ density to about 550 m-2. The new O group began to appear in October-November, as aggregates below 3 cm sediment depth, believed to represent lecithotropic, direct-developing, siblings from egg masses of the II+ group. Juvenile setiger-total frequencies indicated synchronous adult spawning occurred at varying intervals during an approximate six month period. Peak density of dispersed, near-surface recruits reached 29 thousand m-2. Setiger-total was the most sensitive indicator of size and age in juveniles of up to about 15 setigers. Zonation patterns were age specific. The predominantly lower-shore capitellid, Heteromastus filiformis had a short summer spawning period with settlement ending before May, when population density was up to 10 thousand m-2. Merger of O group into the adult size range occurred in about one year, and probably first spawning was at the end of the second year, with life span of three years or more. The nereidid Nicon aestuariensis had I+ and older age groups at barely detectable densities. Spawning was probably in late summer although an O group, at about 500 m-2, was not detected until May. The spionid Scolecolepides benhami had apparently unchanging size structure and density (about 400 m-2 transect-wide); new settlement was not detected. High density occurred only in a narrow near-shore strip. Nicon aestuariensis also declined down-shore, but more gradually. The spionid Microspio sp. and capitellid Capitella sp. were short-lived, near-surface species, with apparently continuous recruitment from planktotrophic and direct-development respectively. A spring recruitment increase created at first a separate modal group of juveniles, and raised Microspio sp. density to 45 thousand m-2 and Capitella sp. to 7 thousand m-2. Capitella sp. declined in density downshore, but Microspio sp. was only weakly zoned. The common polychaetes had largely concordant density cycles with settlement (or peak settlement) spring-summer orientated, although 500 micron mesh processing detected the peak of surviving adults in autumn-winter. Pauatahanui polychaetes as an assemblage, life history traits, links between population structure and zonation, and problems in polychaete population studies are discussed.</p>

First thorough assessment of de novo oocyte recruitment in a teleost serial spawner, the Northeast Atlantic mackerel (Scomber scombrus) case

The understanding of teleost fecundity type (determinate or indeterminate) is essential when deciding which egg production method should be applied to ultimately estimate spawning stock biomass. The fecundity type is, however, unknown or controversial for several commercial stocks, including the Northeast Atlantic mackerel (Scomber scombrus). Aiming at solving this problem, we applied state-of-the-art laboratory methods to document the mackerel fecundity type, including any de novo oocyte recruitment during spawning. Initially, active mackerel spawning females were precisely classified according to their spawning status. The number and size of all phasei-specific oocytes (12 phases), with a special attention to previtellogenic oocytes phases (PVO [PVO2 to PVO4a–c]), were also thoroughly investigated. Examinations of relative fecundity (RFi) clarified that the latest phase of PVOs (PVO4c) are de novo recruited to the cortical alveoli–vitellogenic pool during the spawning period, resulting in a dome-shaped seasonal pattern in RFi. Hence, we unequivocally classify mackerel as a true indeterminate spawner. As PVO4c oocytes were currently identified around 230 µm, mackerel fecundity counts should rather use this diameter as the lower threshold instead of historically 185 µm. Any use of a too low threshold value in this context will inevitably lead to an overestimation of RFi and thereby underestimated spawning stock biomass.