\u3cem\u3eChlamydomonas\u3c/em\u3e mutants display reversible deficiencies in flagellar beating and axonemal assembly

Axonemal complexes in flagella are largely prepackaged in the cell body. As such, one mutation often results in the absence of the co-assembled components and permanent motility deficiencies. For example, a Chlamydomonas mutant defective in RSP4 in the radial spoke (RS), which is critical for bend propagation, has paralyzed flagella that also lack the paralogue RSP6 and three additional RS proteins. Intriguingly, recent studies showed that several mutant strains contain a mixed population of swimmers and paralyzed cells despite their identical genetic background. Here we report a cause underlying these variations. Two new mutants lacking RSP6 swim processively and other components appear normally assembled in early log phase indicating that, unlike RSP4, this paralogue is dispensable. However, swimmers cannot maintain the typical helical trajectory and reactivated cell models tend to spin. Interestingly the motile fraction and the spokehead content dwindle during stationary phase. These results suggest that (1) intact RS is critical for maintaining the rhythm of oscillatory beating and thus the helical trajectory; (2) assembly of the axonemal complex with subtle defects is less efficient and the inefficiency is accentuated in compromised conditions, leading to reversible dyskinesia. Consistently, several organisms only possess one RSP4/6 gene. Gene duplication in Chlamydomonas enhances RS assembly to maintain optimal motility in various environments

Observations on the Food and Feeding Habits of the Skipjack Tuna, Katsuwonus pelamis (Linnaeus) from Minicoy, Lakshadweep

The food and feeding habits of the skipjack tuna based on the data for the period 1993-96 is given here. Fishes, Cephalopod and crustaceans formed the main food items. Among fishes. Der.u/~lerri.ss p. is the dominant species found almost throughout the year. Cephalopod is fully comprised by squid. In prawns, Thula.s.socari.s sp. was seen during June-August and Lrl,tochela sp. during October-December. But in general empty condition dominated. The feeding habits in relation to the catch is discussed in addition to the comparison of the present observation with the earlier studies from here

Tuna livebaits

The fishery, biology and dynamics of livebaits used in the tuna pole and line fishery are discussed based on earlier and current work. Their catch in Minicoy showed interannual variation with an average of 7569 kg and CPUE of 2.5 kg. Clupeids dominated forming 39.5% followed by caesionids[32. l%).apogonids(22.5%} and pomacentrids(5.6%). At Agatti, the mean catch was 52 tonnes with a CPUE of 14 kg comprised exclusively of Spratelloides delicatulus. Biological characteristics such as size,food and feeding, sex-ratio,size at first maturity, spawning and fecundity, length-weight relationship etc of dominant species are given. Stock assessment studies on S. delicatulus and Archamia fucata indicated their over exploitation. Various measures for management and conservation of the resources along with future research priorities are indicated

Seasonal hand line fishery for yellowfin tuna at Colachel

In Tamil Nadu, the oceanic tunas like skipjack and yellowfin tuna are exploited mainly by multiday drift gill netters. However, in Colachel, Kanyakumari, there is a seasonal fishery targeting yellowfin tuna of medium size weighing around 30 kg, with hand lines that are operated from multiday trawlers. This is an additional income for both the fishermen and the trawl boat owners

Tuna live-bait fishes - their exploitation, conservation and management in Lakshadweep

The total annual catch of baitfishes form pole and line fishing areas of Lakshadweep is estimated to be 1251. At Minicoy, the average annual catch is estimated at 9.11 and at Agatti it is estimated to be 51 t. Data from other baitfish fishing areas such as Suheli, Valiapani and Cheriyapani are virtually non-existent. Management options suggested earlier include the collection of fishery data from more areas, studying the biology and understanding the stock of exploited species, culture of suitable species and maintaining the health of the coral reefs of the islands. Future thrust areas for research to elucidate the factors that determine the baitfish fishery include a full review of the existing fishery and development of a baitfish statistics collection system

On the fishery and some aspects of the biology of dogtooth tuna, Gymnosarda unicolor (Ruppell) from Minicoy, Lakshadweep

The results of a study, on the fishery and biology of dogtooth tuna, Gymnosarda unicolor (Ruppell), conducted at Minicoy during 1995 to 1999 are presented. The resource is exploited from around the reef areas during July-August or September for sustenance when the usual fishing activities like pole and line and trolling are suspended. The total catch in a season varied from 56 to 481 kg. The size ranged from 44 to 126 cm fork length with the modal group at 58 and 62 cm. The length-weight relationship was found to be Log W = -4.5337 + 2.77 Log L. Fish below 70 cm size was found to be immature

Van der Waals Engineering of Ferromagnetic Semiconductor Heterostructures for Spin and Valleytronics

The integration of magnetic material with semiconductors has been fertile ground for fundamental science as well as of great practical interest toward the seamless integration of information processing and storage. Here we create van der Waals heterostructures formed by an ultrathin ferromagnetic semiconductor CrI3 and a monolayer of WSe2. We observe unprecedented control of the spin and valley pseudospin in WSe2, where we detect a large magnetic exchange field of nearly 13 T and rapid switching of the WSe2 valley splitting and polarization via flipping of the CrI3 magnetization. The WSe2 photoluminescence intensity strongly depends on the relative alignment between photo-excited spins in WSe2 and the CrI3 magnetization, due to ultrafast spin-dependent charge hopping across the heterostructure interface. The photoluminescence detection of valley pseudospin provides a simple and sensitive method to probe the intriguing domain dynamics in the ultrathin magnet, as well as the rich spin interactions within the heterostructure.Comment: Supplementary Materials included. To appear in Science Advance

Tuna drift gillnet fishery at Chennai, Tamil Nadu- an update

The present study describes the status of multiday drift gillnet fishery for tuna from Chennai fishing harbour based on data for the years 2016 – 2017. The data is also compared with that during 1999- 2006. Both the craft and gear increased in size with consequent extension of fishing grounds and increase in the number of days/ fishing trip. The size of the boats increased to 20-23 m OAL from 11-12 m OAL and weight of the gear from 1 to more than 6 t. Annual average catch increased to 8523 t during 2016-2017 from 595 t during 1999-2006. Average catch per unit effort was 8310 kg as against 730 kg during 1999-2006. Yellowfin tuna, Thunnus albacares and Skipjack tuna, Katsuwonus pelamis were the dominant species. The stock position of skipjack tuna and yellowfin tuna vis-àvis the three indicators indicated that the percentage of mature yellowfin tuna in the catch in 2017 was 68%, fish in optimum length 35% and mega-spawners 33% whereas in skipjack tuna the respective percentages were 99.5, 21.1 and 79.1. Problems and prospects of multiday tuna drift gillnet fishery are also discussed

Problems and prospects of marine fisheries at Lakshadweep

The Lakshadweep sea is estimated to have an annual fishery potential of about 90,000 tonnes while the present yield is only about 6000 tonnes. ' Endowed with vast lagoons and tuna-rich oceanic waters, I fishing is an important component of the economy of Lakshadweep. Tunas form 87% of the fishery and is caught mainly by the pole-and-line technique-:-This method involves locating the tuna shoals, then attracting by chumming with live bait and water spraying, and finally, catching the fish using poles and lines with barbless hooks

Distribution and abundance of carangids along the EEZ India

Distribution and abundance of carangid groups of fish along the EEZ of India based on the data collected during 80 cruises undertaken by FORV Sagar Sampada is presented here. East coast of India showed maximum concentration of ctrangids with a catch rate of 64 kg/hr along the northeast coast. The least distribution was noticed along the northwest coast ( 5 kg/hr). Carangids formed up to a maximum of 19 % of the total bottom trawl catch along the northwest coast. With more than 20 species of carangids reported to be caught in various cruises, Decapterus spp formed the most dominant group, followed by species like Atule mate, Selar crumenophthalmus, Carangoides malabaricus etc. Depthwise distribution showed higher density in the 60-80 m range all along the coast excepting the Andaman-Nicobar archipelago. Areawise, higher densities of carangids were noticed at latitude-longitude 7°N - 77°E, 1TN - 75°E, 1TN - 79°E, 14°N - 80°E , 18°N - 72°E, 19°N -85°E and 19°N -86°E. Seasonally, carangids were represented in the catch more during the monsoon especially along the northeast and southwest coasts. Potential yield of carangids along the EEZ of India is estimated to be 94971 tonne