The Pearl Banks inspection: April, 1970

The last major pearl fishery in the Gulf of Mannar was held in February-March, 1958, when about 4.5 million oysters were collected from the south-west Cheval Paar by dredging. (Sivalingam 1961). Subsequently, two smaller fisheries, one in 1960 and another in 1961 took place. In these two fisheries one million oysters and four hundred thousand oysters respectively were collected from the Cheval paar by dredging. (De Fonselm 1953). Inspections of the Banks were carried out in 1962, 1963, 1964 and 1965. (Balasuriya 1964 and Silva 1965 and 66). Since then inspections were not possible due to one of two reasons or both the non-availability of operational dredges and a suitable vessel for this type of work.The "Pesalai" a 235-ton stern trawler was made available by the Ceylon Fisheries Corporation management for the 1970 inspection. Two new 6-foot dredges turned out by the Government Factory were also available for this work. However, the survey was limited to 3 days-the period for which the vessel had been released. It was further limited to those areas of the banks over 6 fathoms in depth because of the risk in operating a large vessel in shallower depths.

Biology of fouling in Neendakara port, a tropical estuary in the south west coast of India

Species composition and some aspects of the biology of the fouling community in Neendakara port (southwest coast of India) has been examined for a period of one year. Fouling organisms were collected with a system of glass panels exposed for varying durations and during different months in the port. One species of sponge, nine species of coelenterates, thirteen species of polyzoans, four species of mud-tube dwelling polychaetes, four species of serpulids, one species each of mud-tube forming amphipod and tanaid, two species of oysters, six species of mussels and not less than eight species of tunicates were the macro fouler which settled over the panels. Monthly and seasonal settlement of the different species has been recorded. Fouling has been a continuous process occurring throughout the year in Neendakara port with slightly fluctuating biomass and considerably varying species composition. Alternate species dominance of marine and brackish water forms has been an important feature of fouling in the area. Number of species of the sedentary fouling animals represented on test panels has been high during the highly saline pre-monsoon period and low during the monsoon period.

A bacteriological study of the natural flora of edible oyster, Crassostrea madrasensis

The total viable bacterial populations in the oysters and the sea water from the edible oyster farm at Tuticorin were in the range of 10 super(3) to 10 super(4) per ml and 1 super(2) to 10 super(3) per ml respectively. The maximum most probable number of faecal coliform recorded during the one year period of study of both the oysters and seawater were 33 per 100 ml. Pathogenic bacteria (Salmonella sp., Vibrio cholerae, coagulase positive staphylococci and faecal streptococci were absent in oysters and farm water. Study of 197 (98 taken from oyster liquid and 99 from oyster farm water) randomly isolated cultures indicated that gram negative asporogenus rod-like bacteria of the Vibrio, Flavobacterium, Achromobacter and Pseudomonas groups were the dominant flora of the oyster liquid as well as seawater.

Canning of edible oyster meat

Results of experiments carried out on canning edible oyster (Crassostrea madrasensis) meat from farmed as well as wild specimens are discussed. The canning yield of meat was 15% higher from farmed oysters compared to wild specimens. The meat from wild oysters was highly slimy and therefore required an additional pre-treatment of washing in brine containing acetic acid to prevent formation of lumps of meat in the can causing problems for proper heat penetration while processing.

Height-depth (breadth) relationship of shells in the backwater oyster Crassostrea madrasensin (Preston) of the Cochin harbour

A study of the height-depth relation in the Indian backwater oyster Crassostrea madrasensis (Preston) was carried out. The plot of height against depth showed an exponential trend and a relationship of the form H = ADB. Plot of height against depth also showed larger deviations in height for oysters with greater depth. Analysis showed that variations in height do not result in corresponding variations in depth, particularly in oysters with increased height.

Height-length relation of shells in the Indian backwater oyster Crassostrea madrasensis (Preston) of the Cochin harbour

Height-length relationship in Crassostrea madrasensis (Preston) showed an exponential trend and relation in the form, H=ALᴮ. Deviations of actual values from the mean values consequent to the increase in size were noticed. Height and length approximated in oysters of less than 3.5cm in height resulting in orbicular shape. In oyster of shell height 3.5cm to 8cm, increase in height is faster leading to an oval shape. Above 8cm in height, the oysters become further elongated. Height-length relation is non-linear with an index (B value) of 1.1156. A linear relationship also holds good as the B value is not very much different from unity (H=-2.5424+2.0036L).

Experiments on the induced spawning and larval rearing of the milkfish, Chanos chanos (Forsskal) in 1979

This paper summarizes the results of the experiments on the induced breeding and larval rearing of milkfish (Chanos chanos) during the 1979 season. Milkfish larvae could be reared successfully without the use of trochophore larvae of oysters as feed during the first few days. In order to induce the ovulation of wild adult milkfish a higher dose of human chorionic gonadotropin hormone is required.

Condition index and percentage edibility of Crassostrea madrasensis (Preston) inhabiting the Cochin Harbour

Monthly variations in condition index and percentage edibility of the population of oysters, namely, Crassostrea madrasensis (Preston) is reported for males, females and indeterminates for the period October 1981 to September 1982. Condition index and percentage edibility showed more or less similar trend for the total population and also for males, females and indeterminates. The condition index and percentage edibility were maximum during October 1981 which declined progressively and reached the lowest in February-March, 1982. From April it showed steady increase and reached the maximum again in October 1982 and this coincided with the gonadal cycle in oysters.

Levels of cadmium in seafood products

The concentrations of total cadmium were determined in 448 samples of processed fishery products comprising crustaceans, molluscs, marine fish and brackish water fish. Shrimp product, the major export item, contained on average 0.122 ppm cadmium and 20% of crustaceans analysed did not contain cadmium on detectable level. Average content of cadmium in 68 marine fish of 9 species was 0.153 ppm and 35% of the samples did not contain the element. Of the total number of crustaceans analysed only 2% showed a level > 0.5 ppm. All the 174 samples of molluscan products, except 3 canned oysters, showed cadmium concentration far below the limit allowed. The average cadmium content in molluscan products was 0.552 ppm.

Effects of hydrocarbons on reproductive physiology of the pearl oyster, Pinctada fucata

There are a lot of evidence that show hvdrocarbones cause some defect in reproduction and growth of bivalves. Bivalves are filter-feeder, thus accumulate more hydrocarbones in their tissue. In this study adult pearl producing oysters (Pinctada fucata) are used for all experimens. Samples of oysters, water and sediment from four natural beds; Nakhiloo (clean), Hendurabi (semipolluted), Lavan 1 (semipolluted) and Lavan 2 (polluted) were gatherd for 13 succesive months. Temperature, salinity, pH, oxygen and turbidity were recorded in each sampling. Oysters were kept in laboratory for adapation and then their length (DVM) were measured. Hemolymph samples were collected by insuline syring. Sediments and soft tissues of oysters were dissolved in carbon tetrachloride and when heated to extract oil hydrocarbones. UV, GC and IR were used to assay oil hydrocarbones. Accumulation of hydrocabones in soft tissue were as follows : Kakhiloooysters, major one in late spring and minor one in mid fall. Little elevation of progesterone start gamete and a lot of elevation release gametes_ Esteradiols gradually increase during gametogenesis and reach to maximum level during vitellogenesis. Testosterone have a synergestic role which esteradiol during vitellogenesis and also is effective in male sexuality. Multi regression test showed that there isn't meaning relationship (P<0.05) between hydrocarbones pollution and esteradiols. However in Lavan 2 due to hormone concentration of hydrocarbones had some effect in sexual hormonal cycles. Turbidity was the most effective factor for releasing of progesterone. Progesterone was a stimulating factor for releasing estradiol also release of testosterone was corrolated with oxygen and depth of beds. One way analysis of variance showed that there is not significant relasionship (P<0.05) between different factory in stations.

A review of advances in research on marine molluscan antimicrobial peptides and their potential application in aquaculture

Antimicrobial peptides (AMPs) are important components of the host innate immune response against microbial invasion. They are usually characterized by their small-size, heat-stability and broad range of antimicrobial activity. This review covers research advances on marine mollusc AMPs, specifically those isolated from mussels, scallops, oysters, venerid clams and abalone, which mainly include MGD, mytilin, myticin, mytimycin, big defensin, and RPD-1. Their structural characteristics, antibacterial activity, and expression pattern as well as peptide distribution and their release following microbial challenge are also discussed. In addition, the prospect of the application of AMPs as food additives or their use in immunostimulation to prevent diseases of aquatic animals, as well as their potential hazards, are also discussed.

Alteration of metallothionein mRNA in bay scallop Argopecten irradians under cadmium exposure and bacteria challenge

Metallothionein (MT) is a superfamily of cysteine-rich proteins contributing to metal metabolism, detoxification of heavy metals, and immune response such as protecting against ionizing radiation and antioxidant defense. A metallothionein (designated AiMT2) gene was identified and cloned from bay scallop, Argopecten irradians. The full length cDNA of AiMT2 consisted of an open reading frame (ORF) of 333 bp encoding a protein of 110 amino acids. with nine characteristic Cys-X-Cys, five Cys-X-X-Cys, five Cys-X-X-X-Cys and two Cys-Cys motif arrangements and a conserved structural pattern Cys-x-Cys-x(3)-Cys-Tyr-x(3)Cys-x-Cys-x(3)-Cys-x-Cys-Arg at the C-terminus. The cloned ANT showed about 50% identity in the deduced amino acid sequence with previously published MT sequences of mussels and oysters. The conserved structural pattern and the close phylogenetic relationship of AiMT2 shared with MTs from other mollusc especially bivalves indicated that AiMT2 was a new member of molluscan MT family. The mRNA transcripts in hemolymph of AiMT2 under cadmium (Cd) exposure and bacteria challenge were examined by real-time RT-PCR. The mRNA expression of AiMT2 was up-regulated to 3.99-fold at 2 h after Listonella anguillarum challenge, and increased drastically to 66.12-fold and 126.96-fold at 16 and 32 h post-challenge respectively. Cadmium ion exposure could induce the expression of AiMT2, and the expression level increased 2.56-fold and 6.91-fold in hemolymph respectively after a 10-day exposure of 100 mu g L-1 and 200 mu g L-1 CdCl2. The sensitivity of AiMT2 to bacteria challenge and cadmium stress indicated it was a new Cd-dependent MT in bay scallop and also regulated by an immune challenge. The changes in the expression of AiMT2 could be used as an indicator of exposure to metals in pollution monitoring programs and oxidative stress, and bay scallop as a potential sentinel organism for the cadmium contamination in aquatic environment. (C) 2008 Elsevier Inc. All rights reserved.

Integrated cultivation of the red alga Kappaphycus alvarezii and the pearl oyster Pinctada martensi

The effect of simultaneously cultivating the pearl oyster Pinctada martensi and the red alga Kappaphycus alvarezii on growth rates of both species was investigated in laboratory and field studies conducted from December 1993 to June 1995. The two study sites were in subtidal areas 100 km apart off the east coast of Hainan Island, China. Pearl oysters were cultivated in the center of an algal farm and red alga was cultivated in the center of the pearl oyster farm. These field experiments showed higher growth rates of both P. martensi and K. alvarezii in a co-culture system than in a monospecies culture system. Laboratory studies showed that the algae removed nitrogenous wastes released by pearl oysters. Algae treated with pearl oyster wastes grew much faster than those without oyster wastes. Algae treated with the seawater to which NH4Cl, NaNO3 and NaNO2 were added grew at the same rate as those treated with natural seawater containing oyster nitrogenous wastes, suggesting that enhanced growth of algae in the co-culture system was largely due to nitrogenous metabolites of the pearl oysters. In the co-culture, growth of pearl oysters was positively influenced by the presence of rapidly growing algae but when seawater temperature decreased below 20 degrees C, the algae grew slowly and there was no measurable benefit of mixed culture to either algae or pearl oyster.

小庙洪牡蛎礁巨蛎属牡蛎间生殖隔离研究

中国牡蛎种类丰富，但是由于贝壳可塑性强，表型变化大，分类学及系统发生学研究进展缓慢，存在诸多争议。本文在全国部分海区采集牡蛎样品，并通过表型和分子生物学方法进行鉴定，重点调查潮下带牡蛎的分布情况。选取江苏南通小庙洪牡蛎礁作为典型海域，研究亲缘关系接近的巨蛎属牡蛎之间在繁殖上如何维持相互之间的关系。本研究的目的在于摸索牡蛎物种鉴定的实用方法，并阐明熊本牡蛎和近江牡蛎生殖隔离是如何维持的。研究结果对牡蛎等海洋贝类的分类及系统发生学研究具有一定的借鉴作用，为牡蛎礁的生态保护提供生物学参考依据。 在辽宁营口、海洋岛，河北秦皇岛，山东西霞口、潍坊、青岛，江苏南通，浙江舟山、奉化，福建莆田，广东汕头等地区采集牡蛎样品，重点采集潮下带的牡蛎，通过地理分布、表型、DNA含量测定和COI种特异性探针鉴定对各地区的牡蛎物种组成进行分析。选取了南通小庙洪牡蛎礁作为研究牡蛎物种间相互关系的最佳地点。该地区牡蛎由主要分布在潮间带的熊本牡蛎和主要分布在潮下带的近江牡蛎组成。 对南通小庙洪牡蛎礁上两种巨蛎属牡蛎在空间上的分布进行调查；定期取样，制作性腺切片，观察两种牡蛎的性腺发育情况；同时，定期在海区挂板，采用半人工采苗的方式采集海区牡蛎幼体，通过ITS1基因鉴定采集的稚贝所属物种。通过调查发现二者的分布存在重叠区域；两种牡蛎在2007年6月中旬至9月中旬存在两个明显的繁殖高峰期，在每个繁殖期内两种牡蛎同时发生大量繁殖行为的可能性极高。结果表明，两种牡蛎不存在明显的生态隔离和季节隔离等交配前生殖隔离机制。 在室内对两种牡蛎进行2×2完全双列杂交，并通过ITS1基因的克隆测序验证杂种后代。双列杂交受精实验采用多亲本混合交配的方式（即每个物种的卵子或精子均来自多个个体），共进行7次重复。结果表明，熊本牡蛎的卵子能够被近江牡蛎的精子以较低的受精率（24.6%）受精，且形成的后代确实为两个物种杂交产生，而反方向不能受精。 幼虫和稚贝生长存活的双列杂交实验共进行3次重复。估测受精率、受精卵的孵化率，第1至29日每两天测量一次D形幼虫的壳高和密度。结果表明杂交幼虫（熊本牡蛎♀与近江牡蛎♂的杂交，SA）的受精率（12.5%）显著低于（P < 0.05）熊本牡蛎（75.4%）和近江牡蛎（84.5%）纯种对照组；而孵化率与对照组无显著差异（P > 0.05）；自受精至29日龄，杂交幼虫壳高的生长速度明显低于纯种对照组（P < 0.05）；但是存活率与熊本牡蛎无显著差异（P > 0.05）。杂交幼虫附着变态期间死亡率高；93日龄，熊本牡蛎有10.08%的匍匐期面盘幼虫存活至稚贝，显著大于（P < 0.05）近江牡蛎（2.18%）和杂交幼虫（0.76%）；杂交稚贝壳高显著小于（P < 0.05）纯种对照组。稚贝在海区挂养3个月。与挂养前相比，杂交稚贝在潮下带的存活率为19.2%，125个稚贝仅存24个，壳高平均增加2.15 mm。熊本牡蛎在潮间带的存活率达到65%，壳高平均增加3.99 mm。近江牡蛎在潮下带的存活率达到85.7%，壳高平均增加5.22 mm，在潮间带的存活率仅10.9%，壳高平均增加3.28 mm。受精6个月后，所有杂交稚贝仅剩3枚，运回实验室暂养一段时间后全部死亡。 设置20、25、30、35共4个盐度梯度，估算双列杂交组合在不同盐度下的受精率、孵化率、7日内的存活率和壳高生长，实验共进行3个重复。结果表明，杂交组合在4个盐度下的受精率（平均为11.2%）均显著低于（P < 0.05）熊本牡蛎（75.0%）和近江牡蛎（77.5%）纯种对照组；而孵化率与对照组无显著差异（P > 0.05）；杂交组合在盐度35时的孵化率（85.0%）显著大于20（49.6%）、25（51.3%）和30（55.4%）三个盐度梯度。7日龄杂交幼虫（10.5%）和近江牡蛎（11.4%）的存活率显著小于（P < 0.05）熊本牡蛎（30.3%）；杂交幼虫的壳高（75.7 μm）显著小于（P < 0.05）熊本牡蛎（81.5 μm）和近江牡蛎（85.6 μm）对照组。两因素方差分析表明，杂交组合方式对受精率、孵化率、7日龄存活率和7日龄壳高均有显著影响，盐度对7日龄壳高的影响显著。 实验结果表明，江苏小庙洪牡蛎礁上的熊本牡蛎和近江牡蛎之间在分布空间上存在重叠区域，繁殖时间也存在重叠，并未产生明显的生态隔离和季节隔离。二者之间存在不对称性杂交，熊本牡蛎的卵子能够与近江牡蛎的精子以较低的受精率受精，而反方向完全不亲和。杂交幼虫在受精率上存在显著劣势；但是受精卵的孵化率与纯种受精卵无显著差异；杂交幼虫在生长上也存在显著劣势；而存活率与熊本牡蛎无显著差异；杂交幼虫附着变态期间大量死亡，存活下来的稚贝生长缓慢，死亡率高。表明熊本牡蛎和近江牡蛎之间即存在交配前的配子不亲和性隔离，又存在交配后隔离，主要表现为杂种不活。

Chromosome inheritance in triploid Pacific oyster Crassostrea gigas thunberg

Reproduction and chromosome inheritance in triploid Pacific oyster (Crassostrea gigas Thunberg) were studied in diploid female x triploid male (DT) and reciprocal (TD) crosses. Relative fecundity of triploid females was 13.4% of normal diploids. Cumulative survival from fertilized eggs to spat stage was 0.007% for DT crosses and 0.314% for TD crosses. Chromosome number analysis was conducted on surviving progeny from DT and TD crosses at 1 and 4 years of age. At Year 1, oysters from DT crosses consisted of 15% diploids (2n = 20) and 85% aneuploids. In contrast, oysters from TD crosses consisted of 57.2% diploids, 30.9% triploids (3n = 30) and only 11.9% aneuploids, suggesting that triploid females produced more euploid gametes and viable progeny than triploid males. Viable aneuploid chromosome numbers included 2n + 1, 2n + 2, 2n + 3, 3n - 2 and 3n - 1. There was little change over time in the overall frequency of diploids, triploids and aneuploids. Among aneuploids, oysters with 2n + 3 and 3n-2 chromosomes were observed at Year 1, but absent at Year 4. Triploid progeny were significantly larger than diploids by 79% in whole body weight and 98% in meat weight at 4 years of age. Aneuploids were significantly smaller than normal diploids. This study suggests that triploid Pacific oyster is not completely sterile and cannot offer complete containment of cultured populations.