Effect of nitrite, ammonia, and temperature on P. monodon larvae

P. monodon larvae were studied for the effects of temperature, ammonia, and nitrite on survival. Toxicity levels of nitrite were found to vary with larval stage. Larvae could tolerate ammonia up to about 10 ppm, with the effect more clearly shown by the zoea stage. Survival and growth were not significantly affected by temperature, although moulting was enhanced at temperatures higher than 29 C. Larvae of P. monodon have lower tolerance toward nitrite and ammonia compared to postlarvae. Although high survival was obtained at low levels of nitrite and ammonia, it is still necessary to know their effects on metabolism, in order to examine possible biochemical parameters for diagnosing sublethal toxicity or stress.

Biochemical studies on crab Scylla serrata

Studies on the biochemical composition of crab meat from body and claw revealed marked differences in relation to flavour. Protein content is on the higher side in crabs (19.1 to 20.9%) with high percentage of free amino acids and phosphorus and less carbohydrate and fat. The variation in composition due to the presence of eggs in female crabs and the importance of claw liquor and its composition are reported.

Isolation and culture in artificial media of Lagenidium from Penaeus monodon larvae

Fungal infection of P. monodon larvae is a problem in hatchery operations. The fungus, which attacks the nauplius to postlarval stages and causes up to 100% mortality, has been tentatively identified as belonging to the genus Lagenidium . This pathogenic organism has recently been isolated and cultured. A description is given of the fungus, and features of its biology and pathology are discussed.

Toxicity of malachite green to the larvae of Penaeus monodon Fabricius

A study was undertaken examining the effect of malachite green on the development and survival of the zoeae, mysis and post-larvae of Penaeus monodon. Sensitivity varied with the different larval stages; the zoeae appeared to be the least tolerant. The prophylactic potentials of malachite green in the control of Lagenidiumand Zoothamnium infesting P. monodon larvae are considered briefly. Toxicity risks may be reduced by application between ecdyses or by the removal of the dye by filtration through activated carbon.

Preliminary report on the first production of the crab stages of alimasag, Portunus pelagicus (Linnaeus)

An experiment was undertaken studying the early life history of Portunus pelagicus in order to obtain information of relevance to rearing techniques for crabs.

The use of decapsulated brine shrimp eggs as food for shrimp larvae

Decapsulated cysts of Artemia salina were experimentally fed to the larvae of Penaeus monodon, Metapenaeus ensis, M. endeavouri and Macrobrachium rosenbergii and were found to be comparable to freshly hatched brine shrimp nauplii.

Preserved algae as food for Penaeus monodon larvae

Uni-algal cultures of C. calcitrans, S. costatum, T. chui and Isochrysis sp. obtained from the laboratory were harvested. The harvest, preserved by either freezing or sun-drying, was fed to the larvae of P. monodon . Among the test algal species, Chaetoceros and Tetraselmis were used in larval feeding trials with frozen food while Chaetoceros, Tetraselmis and Isochrysis species were utilized in feeding experiments with sun-dried algae. Their relative effects on larval survival and development were assessed. Results showed that, except the alum-flocculated cells, both frozen Chaetoceros and Tetraselmis can support survival at the zoea stage. Best survival of 68% was atained with dried Chaetoceros followed by Tetraselmis at 44%. Dried Isochrysis did not perform as well, a significantly low survival of only 25% was obtained.

Culture experiments on the copepod, Tisbintra elongata MORI, and evaluation of that species as food organism for milkfish larvae

Five types of food were used to culture T. elongata: rice bran, cow dung, bread, cow dung, bread yeast, fermented fish solubles and Spirulina. Bread yeast was found to give the highest densities. An evaluation was also made of the effectivity of rice bran and fermented fish solubles for the outdoor mass culture of T. elongata . A comparative study on the growth and survival rate of milkfish fry (Chanos chanos) fed with T. elongata and Artemia showed there to be no significant differences between the diets.

In-vitro effect of fungicides on hyphal growth and sporogenesis of Lagenidium sp. isolated from Penaeus monodon larvae and Scylla serrata eggs

The sensitivity of Lagenidium, isolated from Penaeus monodon, Scylla serrata , to 34 antimycotics was determined. Effects on the development of vesicles, zoospores and mycelial growth were evaluated. Although mycoidal levels of the chemicals tested will be ideal for lethal treatment on control of the fungus, the high dose required may be lethal to the host, thus the use of mycostatic concentrations is more practical. Treatments of rearing water containing larvae, adult shrimps or crabs should be done only after preliminary tolerance experiments using at least the mycostatic dose prove to be safe for the hosts. Mycocidal doses can be used for determining disinfection doses of equipment and facilities used in rearing procedures as well as for destroying batches of infected larvae.

Polyculture of milkfish (Chanos chanos) and mud crab (Scylla serrata) at two stocking densities

Mud crabs (Scylla serrata) were cultured singly and in combination with milkfish (Chanos chanos) to compare growth, survival and production rates. Net production of crab was higher in polyculture than monoculture, but the reverse was observed for milkfish.

Culture of the mud crab, Scylla serrata (Forskal) at different stocking densities in brackishwater ponds

The mean weight percentage survival, relative growth increment, net production and feed conversion value of S. serrata stocked in monoculture at different stocking densities are presented.

Results of drift card experiments and considerations on the movement of milkfish eggs and larvae in the northern Sulu Sea

For a period of one year beginning December 1977, drift card experiments were conducted off the western and southern coasts of Panay Island to determine the surface currents in the area. Of a total 2,384 drift cards released during the study, 382 (16.02%) were recovered, 92% of them within 30 days following dispatch. The surface currents in the study area are strongly influenced, in direction and speed, by the prevailing monsoon winds. During the NE monsoon period, the surface currents move away from the coast; during the SW monsoon, toward and/or parallel to the coast. Based on the results, the probable movement and transport of milkfish (Chanos chanos) eggs and larvae from the spawning ground to the fry collection ground are also discussed.

Optomotor reaction of milkfish larvae and juveniles

The development of the optomotor reaction (OMR) in milkfish (Chanos chanos), from the larval, through the metamorphic, to the juvenile stage was observed. The period from the appearance of the pelvic fins until the complete disappearance of the finfold was named ”metamorphic stage”. While the larvae showed strong rheotactic responses, their OMR was somewhat weak. It was clear that the OMR underwent a big change through the metamorphic stage, and became strong and almost perfect in the juveniles.

Fishery of mud crab, Scylla serrata (Forskal) from Karwar waters

Catch data of Scylla serrata obtained in different gears from Karwar region during December 1983 — November 1984 indicated a sum of 9608 kg of landings of crabs. Majority of the crabs (89.57%) was found to be caught in backwaters by line fishing and cast nets. A considerable (10.43%) quantity of catch was also contributed by gill nets and shore-seines from inshore waters. A maximum of 1207 kg of crabs were landed in December, 1983. The size structure and sex-ratio of S. serrata varied with gear type and period.