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.)

Tissue culture in pearl oyster

The first work on cell culture in marine molluscs started since 1960s. Many researchers attempted to improve the culture media composition by adding vertebrate sera as growth factor. In primary cultures, the tissue dissociation methods and medium composition were frequently complemented with homologous and heterologous substanc

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

Glassy Dielectric Response in Tb_2NiMnO_6 Double Perovskite with Similarities to a Griffiths Phase

Frequency-dependent and temperature-dependent dielectric measurements are performed on double perovskite Tb$_2$NiMnO$_6$. The real ($\epsilon_1$) and imaginary ($\epsilon_2$) parts of dielectric permittivity show three plateaus suggesting dielectric relaxation originating from bulk, grain boundaries and the sample-electrode interfaces respectively. The temperature and frequency variation of $\epsilon_1$ and $\epsilon_2$ are successfully simulated by a $RC$ circuit model. The complex plane of impedance, $Z'$-$Z"$, is simulated using a series network with a resistor $R$ and a constant phase element. Through the analysis of frequency-dependent dielectric constant using modified-Debye model, different relaxation regimes are identified. Temperature dependence of dc conductivity also presents a clear change in slope at, $T^*$. Interestingly, $T^*$ compares with the temperature at which an anomaly occurs in the phonon modes and the Griffiths temperature for this compound. The components $R$ and $C$ corresponding to the bulk and the parameter $\alpha$ from modified-Debye fit tend support to this hypothesis. Though these results cannot be interpreted as magnetoelectric coupling, the relationship between lattice and magnetism is marked.Comment: Accepted in Europhysics Letter

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

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

Marine pearl production: CMFRI develops tissue culture technology

Marine pearl production: CMFRI develops tissue culture technolog

Disorder-driven electronic localization and phase separation in superconducting Fe1+yTe0.5Se0.5 single crystals

We have investigated the influence of Fe-excess on the electrical transport and magnetism of Fe1+yTe0.5Se0.5 (y=0.04 and 0.09) single crystals. Both compositions exhibit resistively determined superconducting transitions (Tc) with an onset temperature of about 15 K. From the width of the superconducting transition and the magnitude of the lower critical field Hc1, it is inferred that excess of Fe suppresses superconductivity. The linear and non-linear responses of the ac-susceptibility show that the superconducting state for these compositions is inhomogeneous. A possible origin of this phase separation is a magnetic coupling between Fe-excess occupying interstitial sites in the chalcogen planes and those in the Fe-square lattice. The temperature derivative of the resistivity drho/dT in the temperature range Tc < T < Ta with Ta being the temperature of a magnetic anomaly, changes from positive to negative with increasing Fe. A log 1/T divergence of the resistivity above Tc in the sample with higher amount of Fe suggests a disorder driven electronic localization.Comment: 7 page