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.

Changes and formation of cuticular layers and setae bordering the uropods and endopodites of the pleopods of adult Penaeus monodon were examined under a light microscope. Observations and photographs were made at 0, 12 and 24 hours after molting and every 24 hours thereafter until second molting occurred. Results show that the internal structures of the setae and cuticle undergo marked changes throughout the molt cycle. It was possible to identify the molt stages A, B, C and D. Rapid examination of the molt stages allows the proper timing of eyestalk ablation to induce ovarian maturation.

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.

The culture of grass shrimp, Penaeus monodon has become a fast-growing enterprise in Taiwan since formulated shrimp feed was successfully developed in 1978. In 1983, the total postlarval production for stocking reached 600 million at the price of 12.5 U.S. cents each. This high price of the postlarvae resulted from (1) limited availability of wild gravid females, (2) undesirable spawnings obtained by using the method of eyestalk ablation, manifested by a low average hatching rate of 20%, and (3) high demand from grow-out farms. The eyestalk ablated females induced to spawn were often found unmated which partly explained the poor spawnings and low hatching rates. Consequently, re-use of ablated females was not practised by farmers in the past. The present paper describes the results of artificial insemination and fertilization of wild or pond-reared females whose gonadal development was induced by eyestalk ablation. The hatching rates from unmated soft-thelycum females implanted with two spermatophores are 84.7% and 43.7% while those implanted with only one spermatophore, 74.1% and 16.8%, for the first and subsequent spawning, respectively. These results positively confirm that the unmated condition of ablated females is the main reason for low hatching. Through artificial insemination, the spawning and hatching can be improved and ablated females can be re-utilized. For unmated hard-thelycum females, artificial fertilization was done by releasing spermatozoa into the spawning tank right before spawning. Out of 15 attempts, three were successful with hatching rates of 63.1, 52.3, and 49.9%. Induced maturation of pond-reared shrimps was attempted by manipulation of temperature and salinity. Under constant temperature of 22±2°C, salinities ranging between 25 and 37 ppt were experimented. The best results with 67% success were obtained at salinities of 30 and 35 ppt. Continued efforts will be made to improve spawning performance through the technique of artificial insemination under controlled conditions.

In 1983, penaeid shrimp shipped into the United States from culture ponds in Ecuador were found to have an intense earthy-musty flavor which made them unmarketable. High concentrations of geosmin (trans, 1-10-dimethyl-1-9 decalol), a musty odorous compound, were found in the tail muscle of the shrimp. The level of geosmin, 78 mg/kg muscle, was much higher than levels usually found in pond-cultured freshwater catfish of 13±3 mg/kg muscle. Cause of the rare occurrence of off-flavor in the shrimp is hypothesized to be severe reduction in salinity in the coastal culture ponds which allowed growth of odor-producing blue-green algae.

The embryonic development of the shrimp Penaeus notialis Farfante, 1967 is studied. The duration from spawning to hatching of the nauplii was 14-16 hr. As soon as spawning occurs, a sequence of transformations is observed in the characteristic cell mitosis up to the formation of the embryo which breaks the membrane and emerges as the first naupliar stage. The process of development is very similar to other penaeids and the duration of each stage is characteristic of the species. The influence of salinity and pH on spawning, hatching rate and survival, and the optimal values for each factor were determined.

Utilization of potential area for shrimp culture in the traditional system was very meager — just 1.8% of total estimated available area of 1.45 million ha. The traditional paddy and fish culture and paddy cum fish culture systems and the return on investment (ROI) are explained. To adopt intensive culture, there is adequate scientific information based on many successful achievements throughexperimental trials indicating body weight of 16.7 g in 45 days for P. indicus with more than 80% survival rate proving economic viability. Basic studies were also made to find out the seasonal seed availability in different regions. Shrimp production to the extent of 500-700 kg/ha was achieved in many demonstration ponds organized by the Marine Products Export Development Authority indicating commercial reality of shrimp culture in India. As vast potential areas are available, shrimp culture will minimize the present 75% idle capacity of the Indian seafood processing industry which is over-dependent on shrimp as its major product for export. Furthermore, adding more areas to culture has direct impact on the socio-economic status of the rural population. Three thousand self-employed people are now known to be directly engaged in seed collection. In addition, the shrimp farmer realizes returns two to three times more than his counterpart in paddy cultivation, in the same field and for more or less the same period of time. In West Bengal, of total export value of 43 crores, up to 25 crores is realized by farmers for their production of shrimp through culture reflecting better unit return for their raw material than that realized byprocessor/exporter of the end-product. Therefore, bringing additional areas under shrimp culture will directly affect the socio-economic status of the rural people employing an average of 5 persons/ha, and indirectly affect no less than 15,000 casual workers in the seafood processing industry by additional utilization of manpower and working hours. As productivity from capture appears bleak, brackish-water shrimp culture has been accorded top priority in India's national developmental programmes for more harvest from aquatic sources otherwise termed the "Blue Revolution."

As penaeid shrimp grow from the earliest naupliar stages, through protozoeal and mysis stages, to postlarvae, they develop greater morphological and behavioral resemblance to the adults. Electrophoretic analysis of cytoplasmic enzymes from nauplii, protozoea, mysis, postlarvae, and adults show that each stage has a unique pattern of gene activity. Thirteen enzyme stains and a general protein stain have been used on larval samples from Penaeus stylirostris, P. vannamei and P. aztecus. Some enzymes, such as phospho-glucose isomerase, are produced in the same isozymic form during all of the stages. Other enzymes exhibit changes in the number and position of isozymic bands during development, e.g. glutamate dehydrogenase. Some of these differences among developmental stages can only be explained by changes in the number and/or identity of the genes that are active at each stage. This finding suggests larval and adult responses to selection may be relatively independent.

Ecuadorian Penaeus vannamei were stocked in eight dirt ponds (approximately 163 m2) at four different types of density, i.e., 5 shrimp/m2, 10 shrimp/m2, 15 shrimp/m2, and 20 shrimp/m2. The initial body weight ranged between 1.1 and 3.8 g. No commercial feed was given to the shrimp. The only input to the pond was 30 kg of cow manure/week. Shrimp were sampled either weekly or bi-weekly for body weight measurements. Water quality parameters, such as temperature, pH, DO and turbidity were recorded twice daily; nutrients (nitrite, nitrate, ammonium and phosphate) and BOD were measured twice weekly. The chemical composition of the cow manure was analyzed. After 14 weeks' experiment, the shrimp were harvested, weighed and counted. Survival and total yield were compared among treatments. The results showed negative correlation between stocking density and growth. The weekly growth of shrimp was between 0.7 and 1.0 g. There was no relationship between stocking density and survival. Survival averaged 68%. The most suitable stocking density should be judged by profit. However, the total yield of shrimp was higher in the higher stocking density.

The response of Penaeus monodon juveniles (ave. wt.= 0.076 g) in terms of survival and growth rates to vitamin test diets was observed in a 35-day feeding experiment. The prawns were reared in 60-ℓ oval tanks containing filtered seawater in a flowthrough system of ambient temperature and salinity. The treatments consisted of a control (complete vitamin mix), a vitamin-free diet and nine other diets, each lacking one of the vitamins in the mixture. At the end of the feeding trial, the survival rates in all treatments ranged from 80 to 100%, while weight gain ranged from 74 to 40%. Significantly lower weight gains were obtained from choline chloride-free diet (P<0.05) and vitamin-free and inositol-free diets (P<0.01) than from control.