Effects of stocking density on survival,growth and biochemical composition of cultured mussels (Mytilus galloprovincialis,Lamarck 1819) from an offshore submerged longline system

This study examined an offshore submerged mussel longline system, in the Black Sea, from May 2009 to May 2010. The system was allowed 1 year for spat collection. After a 1‐year spat collection period, some spat collectors were left untouched (NS), and some spat collectors were grazed and socked (S) for a grow‐out study in May 2009. The effects of stocking density on the growth and survival of the S and NS mussels were examined. The biochemical composition of the mussels was also determined. Environmental factors including temperature, salinity, chlorophyll a, total suspended matter, inorganic matter and organic matter were monitored monthly during the experimental period. In May 2010, the mean length and live weight of the S and NS mussels were 60.46 ± 0.60 mm and 53.34 ± 0.37 mm, respectively, and 20.50 ± 0.50 g and 13.11 ± 0.26 g respectively. Mean moisture and ash were 82.35 ± 0.47% and 6.67 ± 0.44% respectively. Mean carbohydrate, protein and lipid were 27.74 ± 2.40%, 57.68 ± 2.15% and 7.91 ± 0.68% respectively. These results indicate that a submerged offshore mussel culture system in the Black Sea can be commercially convenient. In addition, stock management via thinning out of the spat can considerably increase the marketable size of mussels, reduce harvest time and produce better growth.     

Reproductive cycle of the rock oyster,Striostrea prismatica (Gray, 1825) from two locations on the southern coast of Ecuador

The reproductive cycle of the rock oyster Striostrea prismatica was determined at two fishing areas, General Villamil and Ayangue (located on the southern coast of Ecuador), between May 2012 and April 2013. Monthly sampling campaigns were performed at both locations. The tissues were histologically examined to determine gonadal index (GI), oocyte development, follicular area coverage and sex ratio. Surface seawater temperature, salinity and chlorophyll a concentration were measured during samplings. Our results show a similar annual reproductive pattern at both locations. The GI reached maximum values during the summer. Oysters reached highest ripeness in January and February, while spawning occurred in February–March. Gametogenesis was linked to a consistently increasing follicular area (from 1.3 ± 0.7% to 85.8 ± 7.8%) and associated to surface seawater temperature. Spawning coincided with warm water temperature fluctuations and a seawater salinity decrease. No correlation was found with Chlorophyll a concentration. The sex ratio of sampled populations was 1:1, suggesting that oysters sizing more than 10 cm in shell length present a stable sex proportion in the population. The diameter of mature oocytes was significantly reduced (32.7%) during histologically preparations in comparison to fresh oocytes. Our study provides useful information of environmental factors that may control the observed gametogenesis and spawning activity of S. prismatica.     

Growth and survival of the winged pearl oyster Pteria sterna (Gould, 1851) in suspended culture in the tropical Eastern Pacific: Influence of environmental factors

The growth, survival and influence of environmental factors were analysed in two cohorts of cultured Pteria sterna in Ayangue Bay, Province of Santa Elena, Ecuador (tropical Eastern Pacific). Juveniles representing cohorts I and II (8.4 ± 0.54 and 5.0 ± 0.17 mm in dorso‐ventral axis) were deployed in November 2015 and February 2016, and grown in pearl nets suspended in a long line for 12 and 10 months respectively. The stocking density was monthly and bi‐monthly reduced during sampling of individuals to determine growth in dorso‐ventral shell axis, dry mass of shell, soft tissues and dry mass of fouling on shell. Water temperature, salinity, total seston and phytoplankton biomass (chlorophyll a) were determined at the culture site. Results showed that P. sterna reached ~100 mm in length during the first year of culture. Although little negative influence of environmental factors was detected, high temperatures during the reproduction period can be the most negative influential trait. The highest tissue mass (6 g), which occurred at the 10th month of cultivation, as well as a high availability of spat by artificial collectors in the coastal waters, showed that the species can be considered a good candidate for aquaculture in the tropical eastern Pacific.     

DNA fragmentation in blue mussel (Mytilus edulis) sperm: aquaculture and fisheries implications

The objective of this study was to assess sperm DNA longevity in blue mussels (Mytilus edulis) using a dynamic assessment of sperm DNA fragmentation (SDF) after sperm activation. Mature blue mussels (n = 57) in Vigo (Galicia, Spain) were obtained, specifically rope farmed blue mussels (n = 38) and wild blue mussels (n = 19). After the sperm collection, a subsample was assessed for SDF (0 h), while the rest of the sample was incubated for 6, 9, 12, 24 and 48 h at 15°C, assessing each time point using the Sperm‐Halomax kit (Halotech DNA, Madrid, Spain). The Kaplan–Meier estimator, log‐rank (Mantel–Cox) test and Mann–Whitney U‐test were used for statistical analyses (spss v. 16.0), α = 0.05. The rate of SDF (r‐SDF) between rope farmed and wild blue mussels over 0–6 h incubation was not significantly different (P = 0.278), but was for 6–24 h (P = 0.004). Differences in r‐SDF were observed when comparing the means between the two groups (P < 0.0001). Individual differences in r‐SDF existed among the rope farmed (P < 0.0001) and wild blue mussels (P < 0.0001). Wild blue mussels presented a higher DNA longevity than the farmed blue mussels. Selection of blue mussel males with a low level of sperm DNA damage and greater sperm DNA longevity may result in better fertilization and seed production.     

Settlement and growth of the mussels (Mytilusgalloprovincialis,Lamarck, 1819) on different collectors suspended from an offshore submerged longline system in the Black Sea

A study of spat settlement of a submerged longline mussel culture system was carried out in Sinop area, Black Sea, between May 2008 and May 2009. The effects of six different types of collectors on spat settlement and growth were investigated. Six different types of spat settlement rope were used as polypropylene ropes with 18 mm diameter, 18 mm diameter timeworn silk rope, 22 mm diameter rope made from old hawser (OSR), 22 mm diameter ropes made from old anchovy net without pegs, 18 mm diameter old used nylon ropes and 18 mm diameter tasselled polypropylene ropes. Monthly temperature, salinity, chlorophyll‐a, total suspended matter, inorganic matter and organic matter were determined during the experimental period. The best settlement was observed on the OSR type when measured per metre (3450.00 ± 125.83 ind m^?1). Consequently, the findings showed that settlement preference of spat occurred according to rope structure, and if ropes are designed to combine numerous well‐fixed tassels, spat settlement can increase. Spat growth was affected by environmental factors and rope structure. In addition, the study revealed a negative relationship between density and growth.     

Growth and mortality of Mediterranean mussel Mytilus galloprovincialis Lam., 1819, in relation to size on longline in Mersin Bay, Izmir (Turkey – Aegean Sea)

The growth and mortality rate of different size of mussels, Mytilus galloprovincialis, were compared in Mersin bay, Izmir. Mussel sampling was performed on a monthly basis over 1 year, together with hyrobiological parameters. Water temperature, salinity, chlorophyll a, total particulate matter (TPM) and particulate organic carbon (POC) were determined. Average chlorophyll a, TPM and POC values were 3.88±1.62 μg L⁻¹, 13.12±3.68 mg L⁻¹ and 252±121.89 μg L⁻¹ respectively. Initial mean lengths of mussels for each size group were 10 mm (9.91±0.25 mm), 20 mm (20.14±0.29 mm), 30 mm (30.66±0.21 mm), 40 mm (40.14±0.21 mm), 50 mm (50.62±0.21 mm), 60 mm (59.77±0.21 mm) and 70 mm (69.47±0.62 mm). Maximum growth in length occurred during the spring–summer months. The annual length increments of mussel size groups were 46.22, 41.42, 30.3, 28.03, 20.63, 16.34 and 12.03 mm from small to large size groups respectively. Small mussels grew faster than large mussels and reached commercial size at the same time. Mortality was <5% for all groups at the end of the experiment.     

Environmental factors influencing the reproduction of an estuarine penaeid population and implications for management

This study determined environmental factors influencing the reproductive dynamics of a recreationally fished penaeid Metapenaeus dalli Racek in the Swan–Canning Estuary, south‐western Australia, during a restocking programme. Prawns were collected from nearshore (<2 m deep) and offshore waters (>2 m deep) every lunar month from October 2013 to March 2016. Reproduction occurred between November and March, when water temperature was >17°C, salinity >25 and stratification (bottom–surface salinity) <3. Densities of gravid M. dalli were highest in November of each year when 0+ females matured (19 mm; ~56% asymptotic length) and were highest in the Lower Canning Estuary. Individual fecundity ranged from 34,000 (18.1 mm carapace length [CL]) to 132,000 ova (27.1 mm CL). Egg production peaked in December/January and differed among years, being greatest in 2015/2016. These results suggest that closing fishing between November and December would protect breeding aggregations of M. dalli in inshore waters.     

The effects of salinity on reproductive development and egg and larvae survival in the spotted scat Scatophagus argus under controlled conditions

In the present study, we report the first successful instance of controlled reproduction in Scatophagus argus, which has recently emerged as a new aquaculture resource. The controlled reproduction process for S. argus was optimized with regard to salinity acclimation. Gonadal maturation was affected by salinity in both sexes. Levels of plasma 17β‐estradiol (E₂) and 11‐ketotestosterone (11‐kT) were salinity dependent and increased significantly with the duration of acclimation. Plasma levels of gonadal steroids were higher in fish held at 25‰ salinity. The highest gonadosomatic indices (GSI), 15.1 ± 1.6 in the female and 6.4 ± 1.2 in the male, were also observed at 25‰ salinity. Nevertheless, the optimal salinity for S. argus embryonic development and larval culture was 15‰. Thus, the salinity requirement for gonadal maturation and early development are quite different. The use of advanced reproductive technologies combining salinity acclimation and stimulation of luteinizing hormone‐releasing hormone analog (LHRH‐A₂) resulted in a fertilization rate of 83.2%–91.3% and embryonic survival rates of over 90%. Embryos of S. argus at the 2‐cell, blastula, gastrula and pharyngula stages were observed. Most embryos hatched after 21.0 hr of incubation at 28.0 ± 1.0°C. The development of larvae into juveniles was completed at 40–45 days posthatch (dph). In this study, we provide information about the controlled reproduction of S. argus and identify the optimal environmental parameters for S. argus embryonic and larval culture, with the aim of developing reliable reproductive techniques for its mass production.     

Recruitment of catarina scallop (Argopecten ventricosus) larvae on artificial collectors off the NE coast of the Gulf of California

We evaluated recruitment of larvae of catarina scallop, Argopecten ventricosus, in the area of Puerto Peñasco, NE Gulf of California. We moored artificial collectors in six sites from June 2007 to August 2008 and replaced them every 2 months. We used monthly (July 2002–September 2011) sea surface temperature (SST, °C) and surface chlorophyll‐a concentration (SSChl, mg m^?3) Aqua/MODIS satellite data to describe seasonal environmental behaviour study area. Also, we recorded bottom temperature at each site every 4 h, and every 2 months measured sea surface salinity, temperature and dissolved oxygen. We used a repeated measures anova to evaluate differences in the number of recruited spat between main factors, and analysed the presence of multimodal spat shell size frequency distributions. Overall, spat recruitment was negatively correlated with seawater temperature and showed higher spat recruitment abundances throughout winter, which is the season with the highest surface chlorophyll a concentration. We estimated multimodal shell size frequency distributions characterized by more than one modal size. The natural collection of A. ventricosus spat on artificial collectors in the area can be successfully performed over a protracted period (November–December to May–June). Our results extend the area where collection of A. ventricosus spat can be successful.     

Changes in the spawning habitat of two small pelagic fish in the Northwestern Mediterranean

We investigated the effects of three sea surface oceanographic variables (temperature, salinity, and chlorophyll a) on the abundance of eggs and larvae of two summer‐spawning species in the NW Mediterranean Sea, the anchovy Engraulis encrasicolus and the round sardinella Sardinella aurita, based on data from ichthyoplankton surveys carried out in the 1980s, 2000s, and 2010s. The environmental data showed an increase in seawater temperature and salinity along time, coupled with a decrease in chlorophyll a (proxy for primary production). These long‐term directional changes in environmental conditions helped explain the important reduction observed in the abundance of eggs and larvae of anchovy, as well as shrinking of spawning habitat in this species. At the same time, the probability of occurrence of round sardinella has increased from practically zero in the 1980s to probabilities near 1 along the coastal area of the study region in the two decades of the 21st century. Given that the trends observed in the environmental variables along the three decades of study are expected to continue during the 21st century, as a consequence of climate change, the spawning habitat of anchovy is expected to continue decreasing, while round sardinella habitat can expand. Considering that anchovy is of high commercial importance in NW Mediterranean fisheries, while round sardinella has very low commercial interest, our results show that the viability of small pelagic fisheries in the area may be compromised.