Particle clearance and selection in three species of juvenile scallops

Juvenile scallops (<2 mm shell height) of three species (Placopecten magellanicus, Patinopecten yessoensis, Argopecten irradians) were fed mixed, unialgal cultures. Scallops were fed a total of six algal clones simultaneously and clearance rates were monitored using flow cytometric techniques. In another experiment, scallops were presented with natural assemblages of particulate matter as a food source. Data are presented on differences in clearance rates for the individual algal species as well as size-related differences of algal clones, and uptake of chlorophyll vs. non-chlorophyll cells, both within and between scallop species. Significant differences in clearance rates of individual algal species have been found within and between scallop species. Particle selection does not appear to be based upon size alone and is apparently based on other characteristics of the algae as well. The results demonstrate pre-ingestive sorting.     

Polyculture of sea scallops (Placopecten magellanicus) suspended from salmon cages

Commercial and developmental operations for the culture of the seascallop, Placopecten magellanicus, are present in AtlanticCanada and New England. In an experiment designed to examine the commercialfeasibility of polyculture of scallops with Atlantic salmon(Salmo salar), we measured growth andsurvival of sea scallops grown in suspension at two salmon aquaculture sites innortheastern Maine (Johnson Cove (JC) and Treats Island (TI)). Sea scallop spatwere grown in pearl nets and deployed on drop lines containing ten nets inAugust 1994. One drop line of ten nets was sampled about every four months andscallops were counted, measured and weighed. Scallop tissues were also analysedfor paralytic shellfish toxins (PSP). The maximum level of PSP recorded duringthe study was 1174 g STX equiv.·100 gtissue^–1 (excluding adductor muscle weight). After one year,shell heights were 53.6 and 56.4 mm, growth rates were 0.11 and0.12 mm per day and wet adductor muscle weights were 3.3 and 4.1g (TI and JC, respectively). These growth rates were comparable tosea scallops grown in suspension culture to a nearby scallop aquaculture siteand other areas in Atlantic Canada. Reduced rates of survival were found duringthe latter part of the experiment and were attributable, in part, to heavyfouling, predators and high stocking density. The potential for supplementalincome, diversification of the salmon aquaculture industry, and feasibility ofculturing scallops at adjacent sites to salmon operations does exist.     

Liquid-chromatographic hybrid triple–quadrupole linear-ion-trap MS/MS analysis of fatty-acid esters of dinophysistoxin-1 in bivalves and toxic dinoflagellates in Japan

Fatty-acid esters of dinophysistoxin-1 (DTX1) in scallops Patinopecten yessoensis, mussels Mytilus coruscus, and toxic dinoflagellate Dinophysis species, collected from Japanese seawater, were analyzed by liquid-chromatography mass spectrometry (LC–MS). Precursor ion monitoring, multiple reaction monitoring for 18 fatty-acid esters of DTX1, and full-scan MS/MS spectra obtained with a hybrid triple–quadrupole linear-ion-trap mass spectrometer showed that 14:0, 16:0, and 16:1 esters were the most abundant 7-O-acyl-DTX1 analogues in bivalves. Fatty-acids esters formed by conjugations at hydroxyl positions other than the 7-position of DTX1 were not detected in the bivalves. DTX1 and okadaic acid-16:0 fatty-acid esters have been reported as the most abundant ester in bivalves in several previous studies; however, we found that 7-O-16:1-DTX1 was the most abundant ester in some mussels in which 16:1 was more dominant than 16:0 in the free fatty-acid profile. Comparison between 7-O-acyl-DTX1 and free fatty-acid profiles in the same bivalve samples suggests that polyunsaturated fatty acids are selectively excluded in enzymatic acylation of DTX1. No 7-O-acyl-DTX1 was detected in any single-cell isolates of D. fortii, D. acuminata, D. mitra, D. norvegica, D. tripos, D. infundibulus, and D. rotundata.     

Stock evaluation of giant scallop (Placopecten magellanicus) using high-resolution acoustics for seabed mapping

Survey designs in use for the evaluation of sea scallop stocks do not consider the variability of sediment type, despite strong evidence of its importance for the recruitment and survival of scallops on the sea floor. This study examines the distribution of scallops on Browns Bank, Scotian Shelf, at two test sites, in comparison to sea floor sediment distribution, with particular attention to the effects of small-scale sediment variability on the abundance of the commercially exploited scallop. Important links between scallop abundance, sediment type and habitat structure are described. Scallops are strongly associated with gravel lag deposits, which are readily distinguishable from sand-covered terrain through the use of multibeam backscatter data. There exists a highly significant correlation between scallop survey catch rates and backscatter intensity which can be used for the prediction of scallop stock abundance. Developments in underwater acoustics enable for more precise sea floor mapping and contribute to better estimates of scallop abundance.     

Studies on mass summer mortality of cultured zhikong scallops (Chlamys farreri Jones et Preston) in China

Mass mortalities of cultured zhikong scallops (Chlamys farreri) have occurred each summer in most culture areas of northern China since 1996. Among the hypothesized causes are high culture density, infectious disease and genetic inbreeding. To investigate these potential agents, C. farreri were deployed at three densities (low, medium and high) at three sites (Jiaonan, Penglai and Yantai) in the summer of 2000. Scallops were sampled for survival, growth and histopathology before, during and after a mortality episode. Most of the mortality occurred in July and August, during and toward the later part of the spawning season, when water temperature reached 23–26 °C. Final cumulative mortalities reached 85% to 90% at all three sites. Scallops in the medium and high densities had higher initial death rates than did those at the low density. High densities also inhibited growth. Ciliates from the genus Trichodina, larvae of various organisms and anomalous secretions were observed in sections of the gill cavity, with highest prevalence during and at the end of the mortality period. Prokaryotic inclusion bodies were found in the soft tissues, but their prevalence was low and apparently without correlation with mortalities. Genetic analysis with random amplified polymorphic DNA markers showed slightly lower heterozygosity in the cultured stocks (0.301) than in the wild stocks (0.331). It is possible that the mortalities are caused by a combination of several factors such as stress associated with reproduction, high temperature, overcrowding and poor circulation in the growout cages, opportunistic invaders or pathogens, and possibly inbreeding.     

流沙湾水产养殖区浮游动物群落特征

于2012年5月–2013年1月对流沙湾海区浮游动物进行了周年性的季度调查,共检出浮游动物41种、幼体17类,以桡足类居多(29种)。亚强次真哲水蚤(Subeucalanus subcrassus)、短尾类幼虫(Brachyuran larva)、长尾幼体(Macruran larva)在四季均有出现,并在3个季度中成为优势种。年均浮游动物丰度和生物量分别为48.12 ind./m3、13.43 mg/m3。扇贝主养区、鱼类网箱养殖区和珍珠贝养殖区的各季浮游动物丰度及生物量均低于对照区(非养殖区);大中型浮游动物主要出现在对照区,而在鱼、贝养殖区极少出现。冬季扇贝主养区多样性指数为各区最高,其浮游动物丰度、生物量迅速回升,高于鱼类网箱养殖区和珍珠贝养殖区,但仍低于对照区。研究结果显示,鱼、贝养殖区域流沙湾海区的浮游动物丰度及生物量比往年明显减小,浮游动物的小型化加剧。     

The culture of the southern bay scallop in Tampa Bay, an urban Florida estuary

Bay scallop, Argopecten irradians concentricus (Say), stocks were collected from a Homosassa (Florida) population in 1991 and were kept in seawater from Bayboro Harbor on Tampa Bay, an urban Florida estuary. They were fed with Isochrysis galbana and Tetraselmis sp. Spawning was allowed to occur after the scallops became ripe. The hatching rate of the F1 eggs to D-shaped larvae was 72%. Settlement and metamorphosis began 11 days after fertilization. When spat reached a shell height of 0.8 mm in the laboratory, they were placed with substrates into 300 and 800 m mesh bags, and later in lantern nets, suspended from a dock in Bayboro Harbor. The F1 scallops successfully survived to gonad maturity in the fall of 1992, with mean (sd) shell height of 49.8 (4.0) mm on 6 September 1992. The scallops experienced heavy mortality during the summer, partially as a result of heavy fouling. From early August to October of 1992, F1 scallops grown in Bayboro Harbor were successfully spawned in the laboratory. Growth and survival of the F2 scallops were comparable to those of the F1 scallops. Results have shown that bay scallops can complete an entire life cycle in an urban estuary such as Tampa Bay, and a hatchery for bay scallops on the estuary can assist in the restoration of the population. Fouling represents a possible severe limitation and alternatives to caging for grow-out should be considered.     

Effect of immersion time of cultch on spatfall of the scallop Argopecten purpuratus (Lamarck 1819) in the Marine Reserve at La Riconada, Antofagasta, Chile

A pilot program to evaluate the feasibility of collecting juvenile (seed) scallops using Japanese technology was carried out from October 2001 to April 2002 in the Marine Reserve at La Rinconada, Antofagasta, Chile. The continuous presence of larvae in waters in the reserve allowed for collection of 400–15,340 spat per collector and showed the high reproductive capability of local scallops and the relationship between numbers of larvae in the water and amount of spatfall. Highest rates of settlement were proportional to high numbers of umbone larvae in the water at >5000 larvae m⁻³ when collectors were first immersed. Absence of a relationship between larval numbers and postlarval settlement with trophic factors such as chlorophyll and particulate organic matter in the water suggests that productivity was not limited by these factors. Harvest of spat from collectors immersed for four and five months had recovery efficiencies of 5.5% and 59.4% compared with settlement in collectors after immersion for one month. Cohort analyses of recovered spat suggested that settlement occurred over the lengthy immersion period and was due to the continuous presence of larvae in the water. The loss of a high percentage of spat over the 4–5 immersion period compared with settlement in the first month can be attributed to intraspecific competition of spat density and growth as well as clogging of the collectors by sediment and marine fouling that impeded a flow of water through the nets.     

Response and condition of larvae of the scallops Nodipecten subnodosus and Argopecten ventricosus reared at the hatchery with different seawater sources

Larvae of the scallops Nodipecten subnodosus and Argopecten ventricosus were reared at a hatchery under five seawater sources: (1) filtered seawater, as the control group; (2) pasteurized seawater; (3) seawater taken from a well; (4) synthetic seawater, and (5) seawater containing a commercial probiotic (Epicin). The quality of each seawater source was measured in terms of counts of Vibrio pathogenic bacteria, levels of nitrites, nitrates, and ammonium, and content of suspended and organic matter. Overall response of larvae under each treatment was measured in terms of growth, survival, biochemical composition, and recruitment rate of spat. Differences in all these parameters, as a function of the seawater source, were analyzed with one-way ANOVA. Larvae survived more, grew faster and larger, had higher protein levels, and recruited more in filtered seawater (in N. subnodosus) and pasteurized seawater (in A. ventricosus), but significant differences between treatments were slight. In A. ventricosus cultures, filtered seawater favored significantly higher Vibrio counts than pasteurized seawater, but this result did not affect the response and condition of larvae. The well seawater treatment ranked third in terms of low bacterial counts, high nitrate levels, larvae showing relatively high survival and growth rates, and spat reaching the settlement stage (only in A. ventricosus). The synthetic seawater and Epicin treatments did not yield satisfactory results for any of the indicators measured. In fact, in the Epicin treatment, larvae survived only the first days of hatchery cultivation and settlement occurred only in A. ventricosus. The results from these first set of trials are useful for planning additional experiments aimed to improve the protocol of seawater use at our research hatchery.