Role of microalgae in conditioning water in penaeid larval culture

Microalgae play an important role in conditioning water quality for penaeid larval culture. Recently it has been demonstrated that a modification of the green water larval culture system (Ling, 1969) for Macrobrachium allows the production of post larvae without any water change, despite extensive use of artificial feeds (Ang and Cheah, 1986). Increase of toxic metabolites such as ammonia and nitride are also common in penaeid larval culture, especially where excessive amounts of artifial feeds are employed. Present work examines the use of six marine microalgae at four cell concentrations as a "biological filter" system, to control and detoxify levels of ammonia and nitrite in P. monodon larval culture water whilst using artificial diet. Preliminary results indicate that amongst the six algal species tested, C. japonica at 1000 cell μlˉ¹ was most effective in reducing accumulated toxic metabolites from an unchanged culture water environment.

Seasonal variability in penaeid prawn larval abundance in the Mandovi and Zuari estuaries, Goa

Seasonal variations in the occurrence and abundance of penaeid prawn larvae in the Mandovi and Zuari estuaries of Goa were studied. Larvae and post-larvae of commercially important species viz. Metapenaeus dobsoni (Miers), M.affinis (H. Milne Edwards). M. Monoceros (Fabricius), Penaeus merguiensis de Man and Parapenaeopsis stylifera (H. Milne Edwards) were recorded in that order of abundance. Protozoea and mysis stages were dominant in surface zooplankton collections while the post-larvae were more in the bottom samples. Based on larval density, M. dobsoni appeared to be a continuous breeder. The active spawning periods in other species were during the late post-monsoon and pre-monsoon seasons varying with the species. Peak recruitment of post-larvae in the estuaries was observed mostly during southwest monsoon months (June to September). Penaeid prawn larval ingression was more in the Zuari estuary compared to the Mandovi estuary. Their numerical abundance gradually decreased towards the upstream areas. The feasibility of large scale collection of penaeid prawn larvae for aquaculture is indicated.

Larval ontogeny of a percichthyid fish, Synagrops philippinensis (Günther) in Kagoshima Bay, southern Japan

The larval ontogeny of a developmental series (1.2-8.3mm body length, BL) of Synagrops philippinensis from Kagoshima Bay, southern Japan is described and illustrated. The yolk was completely absorbed in larva of ≥1.5 mm BL. Notochord flexion commenced at about 3.5mm BL and was completed by about 4.0-4.5mm BL. S. philippinensis larvae were distinguished from their congeners based on melanophore patterns, head spination and fin spines and rays. Larvae of 7.5-8.3 mm BL were characterized by anteriorly serrated pelvic spine, two anal spines, nine inner preopercular spines and no melanophore on lateral side of the caudal peduncle; 7.0 to 7.5mm BL larvae by the above characters except serration on pelvic spine; and yolk-sac, pre-flexion, flexing and post-flexion larvae up to 7.0mm BL by unique melanophores on lower lobe of pectoral finfold/fin.

Studies on the induced breeding and post-larval rearing of shing (Heteropneustes fossilis Bloch)

An experiment was conducted on induced breeding and fry rearing of shing, Heteropneustes fossilis (Bloch) in the Department of Aquaculture, Bangladesh Agricultural University for a period of four months from April to July 1994. Hatching rate was calculated at 21.50h and was found to be 45 to 55 % and the survival rate of larvae was 30 to 40 % at 26 to 29°C. Survival rate and growth rate of post larvae were found to be 50 to 60% and 96.6 to 117.2% respectively. Feed-3 (F3) showed the highest survival rate and growth rate of post larvae.

Larval development of a mangrove crab (Perisesarma bidens De Haan) (Crustacea: Brachyura: Sesarminae)

Larval development of Perisesarma bidens (De Haan) was investigated in laboratory conditions. Morphology of all larval stages and 1st crab stage was described and illustrated in detail, and compared with other species of sesarmid crabs. The zoeae morphological features of P. bidens are almost similar to other species of Sesarma in lacking a pair of lateral spines on carapace.

Changes of enzymatic activity during larval development of carp, Catla catla (Ham.)

Quantitative assays of trypsin, amylase and alkaline phosphatases were made in relation to age and food during the larval development of the Indian major carp Catla catla. The responses of all the test enzymes to age and food were identical. No enzymes were detected from the fertilized eggs. Detectable amount of enzymes were first observed in the first day old hatchlings. All the test enzymes in the group fed normal feed tended to rise gradually with advancement of age till day 22 after which an asymptotic level was attained. Absence of food throughout the rearing period caused the enzymatic activity of the larva to remain at the lowest level throughout. When starvation was followed by feeding, enzymatic activity in the former group was consistently higher than that of latter, suggesting that feeding activity was primarily responsible in maintaining the enzymatic activity of carp larva. The enzymatic activity of zooplankton was significantly higher than carp larva till day 6 to 12 after which the latter exceeded the former implying that carp larva during development utilizes the exogenous enzymes of zooplankton.

Post-larval production of Macrobrachium rosenbergii using mass-cultured live food organisms

Macrobrachium rosenbergii post-larvae were produced in 1992 and 1993 using Artemia nauplii and cultured zooplankton Brachionus plicatilis (rotifier), Apocyclops dengizicus (copepod) and Moina sp. (cladoceran) supplemented with chopped Tubifex worms. In 1992 (first trial) two experiments were carried out under water temperature range of 24.5 to 28°C and 26.0 to 28.5 °C respectively and corresponding post-larval production was 5.6% and 86.3%. The duration of experiments was 58 and 40 days. During second trial in 1993 water temperature varied between 25.0 to 27.0°C. At the end of 59 days the post-larvae were found to be 44% of the total number of larvae stocked on the first day.

Substitution of Artemia with Brachionus in different ratios during larval rearing of Macrobrachium rosenbergii and evaluation of their feed efficacy

Larval growth during stage I-VIII was studied in Macrobrachium rosenbergii. Duration in moult periodicity were recorded-during larval development period, larvae were fed with Brachionus (grown on Baker's yeast and also Brachinous raised through organic manuring in outdoor culture containers). The performance of the feed was evaluated through substitution of Brachionus in the feeding protocol, in lieu of Artemia 1st instar. The Artemia, Brachionus substitution ratio of 75:25 was found to be most efficient. The study also indicates that the comparative growth rate of Brachionus plicatilis is higher in manure loaded tanks than with Baker's yeast. Growth rate "Y'' in culture tank being 0.245 and 0.112 and corresponding duplicating time (Td) too was found to be 2.855 and 6.365 respectively in tanks manured/enriched with pig manure.

A Review of the parasitic copepods of fish recorded from Ceylon with description of additional forms

The beginning of our knowledge of the copepods parasitic on fish from Ceylon is due to Bassett-Smith (1898 a) who, in a paper on "Further New Parasitic Copepods found on Fish in the Indo-Tropical Region", included seven species collected at Trincomalee and Colombo. Later in the same year, in a paper on "Some New or Rare Parasitic Copepods from the Indo-Tropical Region", he (Bassett-Smith, 1898 b) included three more species from Ceylon. Soon after, more of these parasites were obtained from Ceylon during Herdmann's investigation of the Pearl Banks. From this collection, one lot consisting of eleven species was described by Thompson and Scott (1903) and a second lot consisting of seven species was described by Wilson (1906). At that stage the number of species recorded from Ceylon made up to a total of twenty-eight and there the matter rested for another quarter of a century until, quite by chance, while collecting marine animals on a reef, Mr Kirtisinghe came across a newly dead half-beak with a learned parasite projecting from its body. Since then, in a number of occasional papers (Kirtisinghe, 1932-35, 1937, 1950, 1956, 1960) he has described thirty-eight more species of parasitic copepods from Ceylon. However, his collection included many more species which were put aside for later attention. In the present paper, while dealing with those forms in his collection which he has not recorded or described earlier, he has put together all the known forms of parasitic copepods of fish from Ceylon. A list of the host fishes with their respective parasitic copepods is also provided, types of new species, at present in the author's private collection, will be deposited in the Fisheries Department, Colombo, Ceylon.

Results of the Austrian-Ceylonese hydrobiological mission 1970 of the 1st Zoological Institute of the University of Vienna (Austria) and the Department of Zoology of the Vidyalankara University of Ceylon, Kelaniya. Pt. 1. Preliminary report: introduction and description of the stations

The Austrian-Ceylonese hydrobiological mission of 1970 investigated and made collections from 36 flowing water systems (brooks, torrents, rivers); of these, 34 water systems were in the mountains regions of south-west and south-east of Sri Lanka. In the crystalline mountain region, the water systems are extremely poor in electrolytes, very soft and slightly acid; these torrential streams have strong falls, high flow velocities and boulder bottoms. The water temperatures increase from the sources and brooks at 2,000 m altitude to the mouths from 15°C to 28°C. The density of animal population (macro and meso-fauna) increases from the river bank regions (and pools) towards the sections with strong current and reaches on the rocks in the cascades a density of 500 to appr. 750 individuals/1/16m².

Rotifera from Sri Lanka (Ceylon) 1. The genus Lecane with description of two new species

The present study is based on collections made from a large number of lakes, ponds and paddy fields during the period 1968-1972. A large number of new records and some new species have been identified in this material. The largest number of species have been recorded in the genus Lecane i.e. Lecane (Lecane), Lecane (Hemimonostyla) and Lecane (Monostyla) and the present paper is restricted to this genus. In all 25 species including two new species are recorded and described.

Larval rearing of a freshwater prawn Macrobrachium gangeticum

Observations were made on the larval development of a freshwater prawn, Macrobrachium gangeticum, which revealed that hatching occurred in freshwater but the larvae failed to survive after 2nd molting. Salinity was necessary for survival of the larvae after 2nd molting. The complete larval development involved nine larval stages and the 10th stage was considered to be the post-larva which measured between 4.5 and 5.0 mm in length. All the larval stages were completed within 26 days of hatching. Specimens from each larval stage were taken out and examined under a microscope.

Effects of salinity and temperature on the larval development of a sesarmid crab Neosarmatium trispinosum Davie (Crustacea: Brachyura: Sesarmidae) from mangrove swamp in Okinawa Island, Japan

The larval development of the semiterrestrial sesarmid mangrove crab Neosarmarium trispinosum was studied under laboratory conditions at salinities 0-35%o and constant temperatures of 20-30°C. The larval development consists of five zoeal stages and a megalopa. Larvae survived to the first crab stage at salinities between 15 and 35%o with different percentages. At 0, 5 and 10%o, the larvae died within 12-18 hours without moulting to subsequent stages. The highest survival rate was recorded at 20-25%o and 25-30°C with shortest development duration to the first crab stage ranging from 24-28 days. At the highest salinity (35%o), survival rate was gradually decreased with increasing development duration. There were significant differences (P

Larval development of Micippa platipes Ruppell, 1930, reared under laboratory conditions (Crustacea, Decapoda, Majidae)

The ovigerous female of Micippa platipes Ruppell, 1830, captured from Buleji (Karachi, Pakistan) on February 7, 1993 and was kept under the laboratory conditions. On February 27, 1993 larvae were hatched in prezoeal stage. The presoeal stage of M. platipes passed through two zoeal stages within three to five days at room temperature (17-20C). The larvae are described, illustrated and compared with the larval account of Micippa thalia (Herbst, 1803) given by Kurata, 1969.