Prawns, like any other animals, exhibit dissimilarities in growth rates. As they grow, a wide range of body weight distribution from the same population is observed. Staggered harvesting method is commonly practised in cultured animals having this characteristic. Selective or partial harvesting is especially useful in this type of management system. In this case, the larger shrimps are caught earlier than the small ones thus giving chance for the smaller ones to grow bigger. The study was conducted in four one-ha ponds. Recommended pond preparation was followed. Partial harvesting was employed in experimental ponds by using 2-4 units of 8 knots selective pound nets once a week commencing after three months culture until final harvest. Control ponds were harvested only once at the end of the culture period. The results show a mean production value of 506 kg from control ponds and 639 kg from experimental ponds. Average survival rate for experimental ponds was higher (92.90%) than for control (77.65%). Final average body weight was higher for experimental ponds (21.8 g) than for control (20.5 g). Size-wise, production of big size group (30-35 g) is 578.0 kg compared to 434.6 kg for small size group (13.1-13.4 g) from both control ponds with over-all production of 1,012.6 kg. On the other hand, production from the two experimental ponds for big and small size groups is 872.2 and 405.8 kg, respectively. The means of the total weights of marketable size Penaeus monodon from control and experimental ponds are 289.0 and 436.1 kg, respectively. That is, 43.5% of the stock reached marketable size in ponds with staggered/partial harvest method compared to only 27.5% from control ponds.

The in vivo effect of mycostatic levels of fungicides against the fungi Lagenidium sp. and Haliphthoros sp. were tested on Penaeus monodon eggs and larvae. Hatching rate and survival of nauplii, zoeae, myses and postlarvae exposed to 10 mg/ℓ Benzalkonium chloride, 1 mg/ℓ Clotrimazole, 1 mg/ℓ Crystal Violet, 10 mg/ℓ 2,4-D, 10 mg/ℓ Daconil, 20 mg/ℓ laundry detergent, 1 mg/ℓ Econazole nitrate, 10 mg/ℓ Resiguard, 0.2 mg/ℓ and 10 mg/ℓ Treflan-R, 0.01 mg/ℓ and 0.2 mg/ℓ Trifluralin were monitored daily for 96 hr in a static bioassay in glass aquaria. Results showed that all test chemicals had no inhibitory effect on hatching rate but survival rate of hatched nauplii was significantly reduced in most treatments except that of 0.2 mg/ℓ Treflan-R. Tests with zoeae, myses and postlarvae indicated that 0.2 mg/ℓ Treflan-R and 0.01 mg/ℓ and 0.2 mg/ℓ Trifluralin did not adversely affect survival. In addition, Benzalkonium chloride caused no significant mortalities among exposed myses.

Penaeus japonicus, P. vannamei and P. marginatus cultured at the Oceanic Institute in Hawaii, were sampled and measured. The shrimps sampled ranged from 1 to 15 g in body weight. The measurements included carapace length (CL), body length (BL), total length (TL) and body weight (BW). The results showed significant linear relationships between TL and CL, BL and CL. The relationships between CL and BW, BL and BW, TL and BW are well expressed by exponential curve. These relationships were found for all three species. However, P. japonicus has more similar morphometric characteristics to P. marginatus than P. vannamei. The carapace portion in P. vannamei is smaller than either P. japonicus or P. marginatus. In other words, P. vannamei has a greater edible portion than P. japonicus and P. marginatus. Equations for length-weight relationships can provide means of converting one characteristic into another.

Earthworm and annelids were incorporated in diets for Penaeus monodon juveniles (mean weight 0.54 g) either in wet or dry form. These protein sources were added in amounts needed to replace 10% of the animal source of protein. Other sources of protein in the diet were shrimp head meal, fish meal, and defatted soybean meal. Diets were computed such that two-thirds of total protein came from animal sources and one-third from vegetable sources. Other components of the diet were rice bran, sago palm starch, cod liver oil and a vitamin-mineral mixture. Another diet, used as maintenance diet, served as control. Postlarvae were randomly stocked at 6 individuals/tank in a flowthrough system with 5 replicates/treatment. Each of the oval fiberglass tanks had three 10-cm diameter PVC pipes for shelter. The prawns were fed 10% of biomass twice daily. Although treatment means for percent weight gain were not significantly different, the diet that contained dried earthworm or annelid meal gave higher weight gain than diets containing the wet form. The earthworm diet gave higher weight gain than diets containing annelids. Survival rate also followed a similar pattern as that of weight gain. Shrimp fed earthworm (wet or dried) gave survival rates numerically higher than those fed marine annelids. Shrimp fed the control diet had survival rates lower than those fed earthworm-containing diets but higher than those fed the wet annelid diet. In another experiment, earthworm or squid was incorporated in the diet. Survival rates of shrimp with earthworm or squid in the diet were significantly higher than those fed the control. Weight gains were not significantly different from each other. Food conversion was generally low. The drawback in the use of earthworm, annelids and squid is that they are relatively expensive compared to fish meal and shrimp head meal.

The effect of salinity and temperature on oxygen consumption at different developmental ages of Penaeus monodon postlarvae (P5 to P60) was studied. The design was a 2 × 5 factorial, using two levels of temperature (15 and 30°C) and 4 levels of salinity (10, 15, 20 and 30 ppt). One-day old postlarvae (P1) were acclimated to various salinities prior to the start of the experiments. Oxygen consumption was determined after three hours using a YSI dissolved oxygen meter vis-a-vis Winkler titration method. Respiratory activity as affected by temperature and salinity varies, dependent on the postlarval stage tested. Statistical analyses showed that temperature did not significantly influence oxygen uptake at early stages (P5-P8) until P25-P28. Its effect started to become apparent when the postlarvae were P35-P38 and was most pronounced at P49-P52. general, the postlarvae consumed more oxygen at higher temperature and the variation in the oxygen consumption of the postlarvae under the two temperatures become less obvious as the postlarvae were older. Salinity seemed to affect the oxygen consumption of the young postlarvae, P5-P8 and P25-P28, more than temperature. Differences in rate of oxygen consumption at various salinities were greater in younger postlarvae (P5-P38) than in older postlarvae (P42_P60). The relationship between rate of oxygen consumption and body weight is nearly linear in the various salinity-temperature treatments. In all cases, the regression was significant at 1% level. P. monodon postlarvae behaved as respiratory con-formers in all the salinities tested at ambient temperatures. The least oxygen consumption rate was noted at salinities of 20 and 30 ppt at low temperature (15°C) and 20 ppt at high temperature (30°C). The importance of these findings is discussed and related to improvement of postlarvae transport methodology.

Ruppia maritima (kusay-kusay, Hiligaynon) and Najas graminea (digman, Hiligaynon) are macrophytes growing in local brackishwater ponds believed to provide food and shelter to prawns and fishes. Their effect on growth and survival of Penaeus monodon juveniles (PL50; carapace length, 4.01 mm; body weight, 0.053 g) were studied in 80-ℓ glass aquaria. The treatments were: (a) a commercial pellet (40% protein); (b) live Ruppia; (c) decaying Ruppia; (d) live Najas; and (e) decaying Najas. The pellet was offered to satiety (approx. 100% of body weight) twice daily. Live Ruppia and Najas were transplanted in the aquaria using pond soil a week prior to the experiment. Decaying Ruppia and Najas were transferred from ponds. Salinity was maintained at 15 ppt and 50% of the water was changed regularly. Highly significant differences (P < 0.01) in mean carapace length (CL) and mean body weight (BW) on the 10th, 20th and 30th days were observed among treatments. Increase in CL was fastest with decaying Najas and slowest in live Ruppia (14% vs. 17% after 30 days). Growth with decaying Ruppia was comparable to pellets on the 10th and 20th days but was faster after 30 days. Body weight on all sampling days was highest in decaying Najas and lowest in live Ruppia. Percentage increases were 122, 273 and 565% on the 10th, 20th and 30th days, respectively, with decaying Najas. Those given live Ruppia registered increases of 11, 67 and 94%, respectively. The rapid growth rate of animals on decaying Najas was compensated negatively by a low survival rate (31%), significantly lower than on live Najas (100%). Other survival percentages were: decaying Ruppia, 59% and pellet, 53%.

As early as half a century ago, Hudinaga successfully spawned and attempted to rear the larvae of Penaeus japonicus. Publications in the 1960 s, 70's and 80's on breakthroughs in larval rearing of one penaeid species after another indicated that practical prawn farming had become a reality. At present, there are 24 Penaeus species and seven Metapenaeus species whose larval rearing techniques are partially or fully established. Among them, only nine species are propagated on a large commercial scale. The other species are now produced only on a small scale or experimentally. There are many published papers dealing with larval rearing techniques of penaeid prawns. However, it is recognized that numerous details and problems remain unsolved pending further investigation and improvement. P. japonicus is the species which boasts the longest research history and the most successful larval rearing techniques. Nevertheless, there is little which scientists are able to do with the serious "white-turbid midgut gland disease" which has plagued the postlarvae of P. japonicus for the past several years. Similarly. P. monodon larval culture in the Philippines was once seriously affected by a fungus disease cause by Lagenidium sp., which resulted in poor survival rate. Suitable larval rearing methods differ from one species to another, all showing varying degrees of modification from the major principles of larval rearing techniques of penaeid prawns. For example, a hatchery can easily obtain several hundred spawners of P. japonicus, but this is never the case with P. monodon. Therefore, the community culture method for rearing larvae in large tanks is preferred for the former species, while the separate tank method, also called the monoculture method, is best for the latter. In general, larval rearing techniques of prawns is at its rapid growing stage. The status of larval rearing including rearing methods, feeding regimes and rearing systems, are herein summarized and introduced. The high priority problems to be solved, such as 1) selection of spawners, 2) improvement of rearing techniques, 3) larval diseases, 4) shipping methods, and 5) social impact are discussed and the prospects of larval rearing are described.

At least five wild-caught Penaeus monodon from various maturation stages (initially classified in vivo as 0, I, II, III, IV, V) were measured, weighed and dissected for histological and histochemical studies. The anterior and posterior parts of the thoracic and abdominal regions of the ovary were sampled and stained with Mallory trichrome, alcian blue-periodic acid-Schiff (AB-PAS) and Sudan black. Results showed that the ovary is composed of the ovarian wall and its extensions, zone of proliferation, follicle cell layer and oocytes. The proliferating cells are less than 10 µm, have thin rims of cytoplasm, and increase in size as maturation proceeds. Based on histology, the stages were finally classified into groups (1) previtellogenic (stage 0), (2) vitellogenic (stages I and II), (3) cortical rod (stages III and IV), and (4) spent (stage V). The previtellogenic group consists only of perinucleolar oocytes (46-72 µm) which are stained negatively with AB-PAS and Sudan black. Oocytes bigger than 55 µm are enveloped by a single layer of follicle cells. The vitellogenic group is composed mostly of yolky oocytes (121-211 µm) with the following cytoplasmic inclusions: small granules of glycoproteins, medium-size globules of lipoglycoproteins, and few large lipid droplets. The cortical rod group consists mostly of yolky oocytes (288-408 µm) with additional rod-like bodies which contain acid and basic mucopolysaccharides but no lipid. The presence of cortical rods is a characteristic feature of mature penaeid ovaries. The spent group is similar to the previtellogenic group but contains some yolky oocytes, thicker follicle cell layers, or irregularly shaped perinucleolar oocytes. Th GSI ranges of the four groups are 0.899-1.937, 3.099-7.598, 5.631-12.000 and 1.848-2.919, respectively.

The response of Penaeus monodon juveniles (0.71±0.11 g) to varying protein/energy ratios in test diets was determined. Purified diets consisting of different levels of protein, lipid and carbohydrates were formulated. Two sets of experiments were conducted with the following diet combinations: (1) 30, 30, 50% protein, 5, 10, 15% lipid and 0, 10, 20% carbohydrate and (2) 40, 45, 50% protein, 5% lipid and 20, 25, 30% carbohydrate. Protein and energy ratios ranged from 89-198 mg protein/Kcal while the energy values for all diets were 165-415 Kcal/100 g. The diets were given twice daily at 10% of the body weight. Results showed that a two- to three-fold increase was observed in the body weight of prawns fed with diet combinations of 40-50% protein, 5-10% lipid and 20% carbohydrate with energy values of 285-370 Kcal/100 g. Reduction in protein content of the diet from 50 to 40% while maintaining the total energy level (285 Kcal/100 g) resulted in a change in growth that was not significant. An increase in energy level, at constant dietary protein level, resulted in improved utilization of protein and feed conversion efficiency.

The tiger prawn of India, Penaeus monodon Fabricius has a differential distribution in the two coasts of India. Density is high in the northeastern part of the Bay of Bengal gradually declining towards the mid-east and becoming quite scarce towards the south. On the west coast, the distribution is more sparse and limited to a few months, off Bombay. The only known inshore areas of capture fisheries are the Godavari estuarine system, and the lagoons off Orissa at Chilka and Madras at Pulicat. The only known offshore capture exists off the Orissa coast at Paradip and Puri extending south to Visakhapatnam and Kakinada Bay. The greatest production comes off the brackishwater "bheri" (wild culture) system in the extensive "sunderbans" of West Bengal on the northeast where millions of seed recruited to the Hooghly estuarine complex are drawn in along with tidal waters and "cultured." The distribution profoundly affects the maturity, breeding and recruitment of this highly euryhaline species. The distribution can be related to the cyclic currents in the Bay of Bengal which have a profound effect on the salinity and temperature profile. It can also be related to the immense quantity of freshwater inflow from the mighty Hooghly-Matlah-Roopnarayan Padma estuarine complex at the head of the Bay and the other major riverine estuaries on the mid-east coast viz., the Mahanadi, Godavari and Krishna. The pattern of circulation and estuarine flows is such that it might also positively influence the food distribution, both live and detrital, in this region. Ripe (gravid) and ripening females and males of P. monodon in the size range of 100-250 g are captured off Paradip coast in the not very deep (30-40 m) waters where coastal trawlers operate, from October through April corresponding to the post-monsoon stability in the water movement and the increasing salinity. This offers a good augury for setting up hatcheries in adjacent zones using naturally mature forms. Catch records from one major freezing plant are presented to indicate the density and distribution of the species at the Paradip-Puri coast.