Showing papers in "Vidyodaya Journal of Science in 1991"

The species composition, abundance and the distribution of seagrass communities in Puttalam lagoon

Abstract: The species composition, abundance and the distribution of different seagrassbeds of Puttalam lagoon have been investigated. Eight species belonging to sixgenera were recorded during the investigation i.e., Enhalus acroida (I. F..)RoyleThalassia hemprichif (Ehrenb.) Aschers., HaIodule uninervis (Forsk.) Aschers inBossiser, Syringodium isoetifolium (Aschers.) Dandy, Cymodocea rotundataEhernb. et Hempr. ex Aschers., Cymodocea serrulata(R. Br.) Aschers, and Magnus,Halophila ovalis (R. Br.) Hook. F. and Halophila decipiens Ostenfeld. Twovarieties of Halodule uninervis (narrow and wide) were also recorded during thisinvestigation. The distribution pattern of the different species of seagrass bedsshowed a close association with different salinity values of the lagoon. It wasfound that the narrow variety of Halodule uninervis covered 75% of the potentialareas of the lagoon. It was also observed that Enhalus acroides, Cymodoceaserrulata and Thalassia hemprichii play a major role as substrata lor manyimportant epiphytic forms of macro and micro algae. It was also discussed thaitraditionalfishing methods prevailing in this lagoon show til great threat to the'survival of the seagrass communities.'

Food and Feeding Habits of the Mud Crab, Scylla serrata Forskal Inhabiting the Negombo Lagoon in the West Coast of Sri Lanka

Abstract: The Mud crab, Scylla serrata is an economically important crustaceaninhabiting the lagoons of the west coast of Sri Lanka Currently there is interestin mass rearing of the species in ponds Thus, a study was carried out to identifythe food and feeding habits of Seylla serrata in the Negombo Lagoon Thestomach contents of crabs of different sizes caught by unbaited gears were screenedto identify the food constituents and it wasfound that crabs of medium size (subadults)mainly fed on molluscs and the small ones (juveniles) on crustaceansMonthly samples were also studied and found that there is no seasonal variationin the food items Diurnal studies were carried out to determine the feeding timeand it became evident that the crabs feed continuously during the night andonly at the high tide in the daytime

The distribution and the species composition of the existing mangrove vegetation around Chilaw lagoon

Abstract: The distribution pattern, species composition, zonation and the abundanceof the mangrove communities around Chi/aw lagoon were studied. 15 typicalmangrove species and 13 mangrove associates were listed. Quadrat sampling analysis shows that most of the western part of the lagoonis dominated by Excoecaria agallocha and Aegiceras corniculatum. Line transectanalysis shows a prominent border to Rhizophora apiculata near the shorearound most parts of the lagoon. Some rare mangrove species such as Xylocarpusgranatum is common in the islands of Chi/aw lagoon. Mangrove area has been reduced due to the new developments and expansiondue to aquaculture.

The role of Tilapia species (family cichlidae) in the fishery of three upland, deep reservoirs of Sri Lanka

Abstract: The fish catches of three upland reservoirs, namely, Kotmale, Victoria and Randenigala reservoirs, were studied for periods of 8, 18 and 9 months, respectively. Tilapia species formed 60-70 % of the catch of all three Reservoirs. Three species of tilapia, namely, Oreochromis mossambicus, O. niloticus and Tilapia rendalli were present in Victoria and Randenigala reservoirs but the last species was not caught in Kotmale reservoir. The three species formed, respectively, 50.8 %. 49.2 % and 0 % of the tilapia catch of Kotmale reservoir, 71.5% 26.6% and 1.9% of that of Victoria reservoir and 96.2%, 2.6% and 1.2% of that of Randenigala ; reservoir . The relative abundance of the three species in the three reservoirs is discussed in relation to that of the three species in other reservoirs in Sri Lanka.

Preliminary observations on the anopheline mosquitoes of gomadiyagala a village in the north western province of Sri Lanka

Abstract: Investigations on anopheline mosquitoes were carried out in Gomadiyagaladuring January-December 1989, primarily to gather base-line data in relationtoa collaborative study between the Entomology Division, Anti-Malaria Campaignand the Department of Zoology, University of Sri Jayewardenepura on thepotential for a genetic approach for malaria control in Sri Lanka Eight anophelinespecies were recordedfrom adult catches and lavae sampled An subpictusAn culicifacies and An varuna were the most predominant species The only stream with two tributaries in the study area was the permanentand very productive anopheline breeding habitat Larval and adult anophelinedensities were related to the rainfall received The larval densities recorded indrought periods were observed to be significantly higher than those recorded inrainy periods (t=4087, p

A Preliminary survey of domiciliary cockroaches and their oothecal parasites in Sri Lanka

Abstract: A survey of domiciliary cockroaches and their oothecal parasites was carriedout in 17 districts. The study was based on empty and live cockroach oothecaecollected from dwelling houses. Five species of cockroaches; Periplanetaamericana (L.) Neostylopyga rhombifolia (Stoll) Periplaneta australasiae (F.)Supella longfpalpa (F.) and Blatella germanica (L.) were found frequentinghouses. Of them, P. american a was the most abundant and widely distributedspecies, while B. germanlca was the least abundant species. P. americana andN. rhombifolia were present in all but one district, while P. australaslae and S.longipalpa were confined to 12 and 08 districts respectively. Mannar districtwas peculiar in that only one domiciliary species, N. rhombifolia was recordedfrom there. Only two species of oothecal parasites, Tetrastlchus hagenowli(Ratz.) and Evania appendlgaster (L.) were encountered during the study. Eachof these parasite species was characterized by the size of the emergence hole theymade in cockroach oothecae. Thus on the basis of the emergence hole alone itwas possible to categorize the empty oothecae as being parasitized. Of theoothecae, those of P. americana and P. australiasae were parasitized by bothspecies of parasites, while oothecae of N. rhombifolla was parasitized by T.hagenowii only. Oothecae of S. longipalpa and B. germanica were not parasitiizedat all. There appears to be a great paucity in the oothecal parasite fauna ofSri Lanka, compared to India where eight species of hymenopterans are known toparasitize oothecae of domiciliary cockroaches. The possibility of controllinghousehold cockroaches using local and introduced parasites remains to be explored.The shortcomings in this preliminary survey are also reported.

Hypotensive activity of crude extract of marine red alagae, Gracilaria SP. in rats

Abstract: Hypotensive properties of the crude extract of Sri Lankan marine red algaeGracilaria sp. of the family Graci/aracea were investigated on anaesthetized ratsusing two doses (250 or 500mg/kg) given intraperitoneal/yo The results showthat the crude extract possesses antihypertensive properties. The extract inducedan immediate fall in systolic blood pressure (within 5 min) which was shortlivedwith the lower dose and sustained with the higher dose. The precise modeof the antihypertensive action is uncertain but is likely to be mediated via decreasedsympathetic activity.

Interrelationships among the secies of the genus puntius (teleostei, cyprinidae) as indicated by the caudal skeletons

Abstract: The studies on the osteology of caudal skeleton and the ray counts showedthat the species of Puntius studied fall into two groups. one containing 11species and the other with one species. The major group with I I species has aprimitive caudal skeleton with 6 free hypurals and 16 or more branched rays,the minor group with one species has an advanced caudal skeleton with 5 freehypurals and 15 branched rays.

Marsh vegetation of Muthurajawela

Abstract: Biologically marshes are among the richest, most productive ecosystemsknown and among the most interesting. Muthurajawela marsh is one such wetland which has a great effect on maintaining the proper ecological balance of themangrove vegetation and the fauna and flora of the Negombo lagoon. An attemptis made here to understand the distribution patterns of vegetation, plantspecies of ecological significance and of special human interest, and to find out,if any, the presence of rare endangeredplants. It is hoped that the present studywould be an initial step for much more detailed ecological studies of theecosystem.

An Investigation into the effect of monocultural plantation of eucalyptus camaldulensis on soil fertility status

Abstract: The effect of Eucalyptus camaldulensis monoculture on soil fertility statusin the dry zone was studied comparatively with another monoculture of Tectonagrandis and a naturalforest located in the same area over a period of 5 months. Total litter production of Eucalyptus was 370.68 kglha as compared with1349.07 kglha in Tectona grandis (study period overlapped the leaf senescence)and 217.75 kglha in the natural forest. Litter decomposition was 40.22% inEucalyptus while it was 40.27% and 44.95% in naturalforest, and Tectona respectively.Nutrient release to litter at the time of fall did not differ between thevegetation types. However, it differed between the tree components and nutrients,the orders being leaves>twigs>bark and N>P>K>Ca. Significant differences (p;;;::0.05)were seen in moisture content, pH, organicmatter content, total nitrogen percentage, available potassium and calcium betweenthe soils in the vegetation types.

Preliminary Observations on the Purse Seine Fishery in the South-west Coast of Sri Lanka

Abstract: Purse seine fishing in the south west coast of Sri Lanka became popularsince 1982 and the number of boats increased to about 29 in 1984. In 1987 therewere around 50 purse seiners operating in this region. A study of the purseseine fishery and its impact on other small scale fisheries were initiated in 1985.The paper presents the results of a surveyfor the period 1985 to 1987. Purse seinefishery is carried out only during the calm months (ie from Octoberto April). 3 1/2 ton boats with inboard engines are used in this fishery.The length of the nets range from 150-210 meters and has an average depth ofabout 50 meters. The average catch per unit effort for purse seiners for 1985/86 season wasabout 185.7 kg/boat. The total production by the purse seine fishery in thisarea in 1987 was about 250 MT. This contributes to about 30% of the totalsmall pelagic fish production in this region. Amblygas.er sirm dominates the purse seine catch. Other importantspecies are Decapterus russelli, Rastrelliger kannagurta and Loligo singhalensis.Length frequency distribution studies of A. sirm show that the purse seiners fishin the same area and probably fish the same stocks as the small mesh gill nettersin this region.

Effect of methanolic extract of abrus precatorius seeds on fertility of female rats

Abstract: This study examines the post-coital contraceptive potential of a methanolicextract of Abrus precatorius seeds using albino rats. The major constituent ofthis extract was found to be abrin, an amino acid derivative (68 % by weight).Furthermore, the extract had no steroidal constituents. Oral administrationof the extract using various dose and time -regimens (single dose of 150mg Ikgon day I of pregnancy; twice daily dose of 150mglkg on day 1 of pregnancy; asingle dose of 300mglkg, on day 1 of pregnancy; and 300mglkg dose from day1-7 of pregnancy) did not suppress fertility significantly. However, a tendencytowards foetal aggregation was evident. It is concluded that the polar fractionsof this seed (presumably abrin), has very little potential as a post-coital contraceptiveagent.

An Analysis of acid vase,ionic and water balance in rainbow trout (salmo gairdneri) exercised at cruising speeds

Abstract: Rainbow trout (Salmo gairdneri) were exercised at cruising speeds for 5hours A slight but significant increase in dorsal aortic blood pH after I hour ofexercise was accompanied by significant decreases in PeDl and total C02content of blood These changes were maintained throughout the exercise periodof 5 hours This respiratory alkalosis could be due to hyperventilation and/orthe result of increased uptake of Na+ and Cl- which occurred along with theincrease in plasma volume in order to maintain normal osmotic concentrationsThe uptake of Na+ and CI- occurred presumably via branchial Na+ /H+ andCI- /HCO2- ion exchange mechanisms