Metabolism in the baby clam Marcia opima

Oxygen consumption and ammonia excretion in different size groups of clam, Marcia opima collected from Tuticorin Bay in Tamil Nadu was studied. Oxygen: Nitrogen ratio was calculated by using atomic equivalents and ranged between 133 - 175 for small, 97 – 117.2 for medium and 63.5 – 75.8 for large clams on day one. After day 3, the range was 238.4 – 282.1, 160.9 – 189 and 100 - 137.5 respectively. During starvation, a decline in excretion rate has been observed, which can be proposed as an index of stress. The study supports interaction of oxygen consumption and nitrogen excretion, which can provide a better understanding of the oxidative and nitrogen metabolism in the clam

The reproductive biology of the baby clam, Marcia opima, from two geographically separated areas of India

A study of the reproductive cycle of the baby clam, Marcia opima (Gmelin) was conducted at two sites along the southeast (Tuticorin Bay) and southwest (Ashtamudi estuary) coast of India from December 1998 to January 2000. Histological evidence showed that baby clam from both the sites showed two spawning seasons. First spawning season was recorded from May to July in the southeast coast. In the southwest coast, the first spawning season was observed through March to May. A second spawning season from September to December was recorded in both the coasts. In the southeast coast, minimum and maximum condition indices were obtained in January 2000 and April 1999 respectively and decreased from May to June and November to January, signifying the two spawning periods. Most of the animals were either in spent or indeterminate gonadal stage from May to August and November to January indicating the active spawning during that months in the southeast coast

The black clam, Villorita cyprinoides, fishery in the State of Kerala, India

The State of Kerala leads India in the production of clams with estimated annual landings of about 66,000 tons (t) in 2008-09. The black clam, Villorita cyprinoides (Family, Corbiculidae) contributes 45,000 t, or about two-thirds of this total (Narasimham et al., 1993; CMFRI Annual Report, 2009). Most of the annual production of black clams, about 25,000 t, comes from Vembanad Lake where almost 4,000 fishermen harvest them. The other clams harvested in the lake are the grey clam, Meretrix casta, and to a much lesser extent, the yellow clam, Paphia malabarica, and another, the Sunetta scripta. Vembanad Lake also has large sub-fossil deposits of black clam shells that are mined for commercial use (Kripa et al., 2004). The lake also has commercially-important finfish. The fisheries for the clams and the finfish provide the major livelihood for coastal communities around the lake (Sathiadhas et al., 2004). This paper provides an overview of the black clam fishery in Kerala including descriptions of the habitats, biology and ecology, demography of the fishing families, and the harvesting, processing, and marketing of the live clams and also the shell deposits. The information provided in earlier papers on these subjects by Laxmilatha and Appukuttan (2002), Sathiadhas et al. (2004), Arun (2005), Ravindran et al. (2006), and others are summarized. We conducted a survey to collect more detailed descriptions of these subjects and supplement them with photographs

A model for responsible black clam fisheries at R-Block in Vembanad Lake, Kerala

Kuttanad is a stretch of low-lying land of about 110,000 ha along the banks of Vembanad Lake and Pamba River tributaries. It encompasses vast stretch of backwaters, bordering human settlements, mangrove forests and rice fields. Four major rivers such as, Pamba, Meenachil, Achankovil and Manimala discharge into this region. It has the distinction of being one of the few areas in the world, where paddy farming is carried out below the sea level. The area is quite famous for its fishery for clams, pearlspot (Etroplus suratensis), snakehead (Channa spp.) and freshwater prawns (Macrobrachium spp.)

Role of co-operative societies in black clam fishery and trade in Vembanad Lake

Lime shells and live clams are distributed in large quantities in the backwaters and estuaries of Kerala. Vembanad, the largest lake of Kerala, also holds a vast resource of lime shells and live clam, comprising several species. The major species that account for the clam fishery of Vembanad Lake is the black clam Villorita cyprinoides. The lime shells that contribute to the fishery are broadly classified as the ‘white shells’ and the ‘black shells’. The so-called ‘white shells’ are sub-soil deposits of fossilized shells and are known to extend upto 7 feet below the lake bottom. The black shells are obtained from the living population of V. cyprinoides, which contribute more than 90% of the clams from this lake

Ferromagnetism and the Effect of Free Charge Carriers on Electric Polarization in Y_2NiMnO_6 Double Perovskite

The double perovskite Y_2NiMnO_6 displays ferromagnetic transition at Tc = 81 K. The ferromagnetic order at low temperature is confirmed by the saturation value of magnetization (M_s) and also, validated by the refined ordered magnetic moment values extracted from neutron powder diffraction data at 10 K. This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The cation-ordered P 21/n nuclear structure is revealed by neutron powder diffraction studies at 300 and 10 K. Analysis of frequency dependent dielectric constant and equivalent circuit analysis of impedance data takes into account the bulk contribution to total dielectric constant. This reveals an anomaly which coincides with the ferromagnetic transition temperature (T_c). Pyrocurrent measurements register a current flow with onset near Tc and a peak at 57 K that shifts with temperature ramp rate. The extrinsic nature of the observed pyrocurrent is established by employing a special protocol measurement. It is realized that the origin is due to re-orientation of electric dipoles created by the free charge carriers and not by spontaneous electric polarization at variance with recently reported magnetism-driven ferroelectricity in this materialComment: Published in Physical Review

Studies on the reproduction of Marcia opima (Gmelin)

The annual reproductive cycle of the clam, Marcia opima (Gmelin) from two geographically separated populations at Tuticorin and Ashtamudi was studied. It was observed that M. opima spawns twice a year at both the places. But the spawning periods are May to June and November to December at Tuticorin and March to May and November to January at Ashtamudi. Fully matured condition of the clam was associated with an increase in the values of gonad index and condition factor and a decrease in the digestive gland index. A slight increase in temperature initiated the spawning activity of M. opima at both the places. The sex ratio at Ashtamudi showed a male dominance. Attempts to induce the maturation of dams showed that fed clams matured faster than the unfed. The gonad index, condition factor and oocyte diameter of clams, kept at 28°C with proper feed was more than that kept at 23°C. Spawning and larval rearing of M. opima were successfully carried out in the hatchery. The settlement of larvae took place on 11111 day. On day 75, the spats attained an average size of 2.81 x 2.37mm. The growth and survival of spats at varying salinities was studied. Maximum growth rate and 100% survival of spat was reported at salinity 25 %0. During biochemical analysis, it was noticed that protein level increases to maximum in the fully matured clams. A low level of carbohydrate was observed during gametogenesis. Lipid level was more in the female gonad than the male gonad. Studies revealed that wet meat weight of clam is directly related to oxygen consumption, ammonia excretion and protein catabolism. The clam fishery at Tuticorin bay constituted a number of species like Marcia opima, Semele striata, Mesodesma glabratum, Gafrarium tumidum, Mactra cuneata and Paphia sp. Allometric relationships of M. opima from both the sites showed a correlation coefficient near to unity between various morphological characteristics. Parasitic infestation was observed in the clams during some months of the sampling period in both the populations

Larval rearing and spat production of Marcia opima (Gmelin)

The ‘baby clam’ Marcia opima (Gmelin) was spawned on seven occasions in the shellfish hatchery at the Tuticorin Research Centre, India. The fertilized eggs measured 47.8 μm in diameter and the straight hinged larvae attained at 20 h were 87 μm in length and 71 μm in height. Settlement occurred on day 9 at 273 μm. The percentage of settlement varied from 13.9% to 56.2%. The growth of post-set clam spat has been described by the equation of L=0.0086x1.4672, where L is the length in mm and x is the number of days. The clam seed reached a size of 11.5 mm at 4 months. The significance of this study is to standardize the techniques for hatchery production of the seeds of M. opima

Effect of culture media and tissue extracts in the mantle explant culture of abalone, Haliotis varia Linnaeus

The study is aimed at developing appropriate media for the mantle explant culture of abalone Haliotis varia. The effect of different media viz., L-15, Ham's F12, M199 was studied in combination with 10% Fetal Calf Serum (FCS) and 10% tissue extracts of gonad, mantle and whole body of abalone, H. varia to understand cell behaviour, cell yield and cell adherence in mantle explant culture of H. varia. Cultures with L-15 media gave better cell yield and M199 promoted better cell adherence. Addition of mantle extract to all media enhanced the cell yield to a maximum followed by whole body extract. Addition of whole body extract facilitated in cell adherence followed by the addition of mantle extract