Seasonal variation of mixed layer depth in the north Arabian Sea

The Arabian Sea is unique due to the extremes in atmospheric forcing that lead to the semi-annual seasonal changes. The reversing winds of summer and winter monsoon induce the variation in the characteristics of mixed layer depth. The importance of mixed layer depth is recognized in studying the biological productivity in the ocean. In this paper variability of mixed layer depth in the north Arabian Sea have been discussed. The study is based on the data collected under North Arabian Sea Environment and Ecosystem Research (NASEER) program. The results of the study indicate that there is a significant variation in the mixed layer depth from summer to winter monsoon as well as coast to offshore.

Mixed culture of fishes in seasonal ponds through fertilization and feeding

A study on mixed culture of mirror carp (Cyprinus carpio Lin.), tilapia (Oreochromis niloticus Lin.), silver carp (Hypophthalmicthys molitrix Val.) and Thai sharpunti (Puntius gonionotus Bleeker) in the ratio of 1:2:2:5 was conducted in 12 seasonal mini ponds (30 m² each) for 105 days. There were six treatments each with two replicates and each pond was stocked with a total of 100 fishes. Rice bran and mustard oil cake were used as supplemental feed either in combination or alone in presence or absence of fertilizer. Fertilizers were used in the form of organic, inorganic or both. The best growth performance of mirror carp, tilapia and Thai sharpunti was obtained in treatment III which received both fertilizer (organic+inorganic) and rice bran while the highest growth of silver carp was obtained in treatment VI receiving only inorganic fertilizer. However, the overall best production (2450 Kg/ha) and economic return for the culture period was obtained in treatment VI followed by treatment III. The results are discussed in the light of water quality parameters.

Effect of different rice brans on the growth of Thai silver barb (Puntius gonionotus Bleeker) in seasonal ponds

An experiment was conducted for a period of 110 days to study the effect of different rice brans on the growth of Thai silver barb (Puntius gonionotus, Bleeker) in rainfed seasonal ponds (30 m² each). Each of the ponds was stocked with 150 fish with the mean initial body weight of 2.03 ± 0.03 g. There were three treatments namely R1, R2 and R3 each having four replicates. Three types of rice bran namely coarse, auto (fine) and red were applied to the treatments R1, R2 and R3 respectively. Fish received different types of rice bran at a rate of 5% of body weight daily. The water quality parameters were found within the productive range. The results showed that treatment R1 produced significantly (p<0.05) highest growth and treatment R2 produced the lowest growth. The survival rates varied between 77 and 84% with treatment R3 producing the highest survival. However, the overall best production (1530 kg/ha) and economic return for the culture period was obtained in treatment R1 receiving coarse rice bran. The results of the present study demonstrated that the coarse rice bran resulted in better growth and production of P. gonionotus.

Seasonal variation in the occurrence of some zooplankton in a fish pond

Observations were made on the seasonal variation in the occurrence of some zooplankton in a fish pond. A total of 31 genera were recorded, out of these, 8 belongs to Rotifera, 5 to Copepoda, 112 to Cladocera, 3 to Protozoa, 2 to Nematoda and 1 to Oligochaeta. The role of temperature, dissolved oxygen, free Co2, pH, turbidity and alkalinity in the occurrence of different genera is discussed.

Observation on the urinogenital papilla and sexual dimorphism in some Indian gobiids (Gobiidae: Teleostei)

A thorough comparative study on the urinogenital papilla and sexual dimorphism has been made for the first time in both the sexes of twelve Indian gobiids: Glassogobius giuris (Hamilton); Acentrogobius cyanomos (Bleeker); Eleotriodes muralis (Valenciennes); Parapocryptes serperaster (Richardson); Apocryptes bato (Hamilton); Scartclaos viridis (Hamilton); Boleophthalmus boddarti (Pallas), Periophthalmus schlosseri (Pallas); P. koelreuteri (Pallas); Taenioides anguillaris (Linnaeus); T. buchanani (Day); Odontamblyopus rubicundus (Hamilton). The urinogenital papilla, originating as a free muscular organ from the ventral surface of the body-wall and shortly behind anus, is present in both the sexes. It is an important organ of primary sex recognition in all species. In case of male the papilla is conical, broad at the base and in female it is either flattened, distally truncated or bluntly rounded. The presence of permanent colour mark over the specific region of the body surface is another secondary sexual character in a few species. Besides, colouration may also be a nuptial secondary sex character developed in some during peak breeding season. The enlargement and colouration of the organ is subject to seasonal variations parallel to the seasonal gonadal cycle. The histological architecture of the papilla shows a high degree of cellular specialization and an interrelationship to the urinary and genital ducts. The functional efficacy and significance of the papilla in the breeding biology of these fishes has been discussed.

Seasonal variation of alginic acid content in Sargassum cervicone Greville from Hikkaduwa

Sargassum cervicone Greville is one of the species of Sargassum occuring in abundance along the South Western Coast of Ceylon. Durairatnam 1966 carried out a survey from Ambalangoda to Hambantota, and estimated that approximately 130 tons of dried Sargassum can be harvested manually. The bulk of the Sargassum found in this area was Sargassum cervicone Greville.

Seasonal variation in the distribution and availability of Carangids ("Paraw" and "Parati") in the Wadge Bank

The Wadge Bank has been exploited regularly by Ceylon based trawlers since 1955 (Sivalingam & Medcof 1957). The bank is about 4,000 sq. miles in extent (Malpas 1926) and is located south of Cape Comorin within the Continental Shelf of India (Fig. 1). Carangids are taken in large numbers during the months of the south west monsoon (Sivalingam 1966). The quantity, in which the Carangids are captured as shown by the fishing records, is large enough to influence the total catch from the bank during these months (Fig. 2). Carangids are held in high esteem as excellent quality food fishes and accordingly constitute a commercially important group. This paper records the results of a detailed examination of the past fishing records in respect of this group, based on the analysis of the catch and fishing effort for the years 1957 to 1962. The distribution pattern of this group of fish in the Wadge Bank is discussed.

Seasonal growth of five commercially important fishes at Sofala Bank, Mozambique

An analysis of growth of scad and mackerels on Sofala Bank, Mozambique, was performed using data collected from commercial vessels during the year 1986-87, using the "Compleat Elefan" software package. Updated estimates of growth parameters of Decapterus russelli, D. macrosoma (Carangidae), and Rastrelliger kanagurta (Scombridae) were obtained which take seasonal growth oscillations into account. Preliminary growth parameter estimates are also presented for Selar crumenophthalmus (Carangidae) and Saurida undosquamis (Synodontidae).

Fish fauna of a coastal lagoon in Sri Lanka: distribution and seasonal variation

In this paper results of investigations carried out over the period of September 1977 to August 1978 are presented. These data were collected in the course of a detailed investigation into the biology and the eco-physiology of the young grey mullet and the grey mullet fishery of the Negombo Lagoon. In this paper the distribution and seasonal variation of fin fish species within the Negombo Lagoon are presented.

Studies on the fish ponds at Pitipana, Negombo 1: seasonal and diurnal variation of some hydrobiological factors

The present paper is a part of a detailed investigation on the biology of grey mullet, Mugli cephalus L., and the feasibility of its culture in the brackish waters of Sri Lanka. The authors present the results of investigation on the water quality of five experimental ponds at the Pitipana Brackishwater Fisheries Station, Negombo, carried out over a period of one year, December 1976 to November 1977, together with studies on the primary productivity are presented.

Duty cycle and modelling considerations in three-phase induction motor drives for washing machines

Three-phase induction motors offer significant advantages over commutator motors in some domestic appliances. Models for wide speed range three-phase induction motors for use in a horizontal axis washing machine have been developed using the MEGA finite element package with an external formulation for calculating iron losses. Motor loss predictions have been verified using a novel high accuracy calorimeter. Good agreement has been observed over a wide speed range at different loadings. The model is used to predict motor temperature rise under typical washing machine loading conditions to ensure its limiting temperature is not exceeded and enables alternative designs to be investigated without recourse to physical prototypes. © 2005 IEEE.

Quantitative and qualitative assessment of plankton: some ecological aspect and water quality parameters of the river Meghna, Bangladesh

Investigation on the seasonal distribution and abundance of various major taxa of phyto and zooplankton and the corresponding physico-chemical characteristics were carried out in four selected stations between the latitude 22°35.494N N-23°23.987 N and longitude 90°35.793 E- 90°49.061 E of the Meghna river system, Bangladesh. Drop count method was followed for the qualitative and quantitative analysis of both phyto- and zooplankton. A total of 41 phytoplankton genera belonging to 17 families and 13 zooplankton genera belonging to 11 families were recorded. Zooplankton growth cycle was noticeably less (3.0%) than the phytoplankton abundance almost throughout the study period. Quantity of plankton registered to increase chronologically from the upper to lower stretches of the river. During summer investigation the load of phytoplankton was recorded maximum (11,300-51,850 No/1). Ratio-wise quantitative difference between zoo- and phytoplankton in composition of the total standing crop fluctuated between 1.0:5.5 and 1:1037. Among the phytoplanktonic groups, Chlorophyceae was found to be dominating (95.0%) in all sampling stations. Protococcus, a single genus of Chlorophyceae played a unique role during summer, contributing the highest density of about 74.0%. The pattern of qualitative and quantitative difference of plankton standing crop in different sampling sites can be attributed to the existing physico-chemical characteristics, mainly water temperature, pH and hardness.