Penaeus monodon collected from brackishwater ponds in Iloilo, Philippines, were induced to become soft-shelled in the laboratory for 3-4 weeks. Eight isocaloric and isonitrogenous diets containing 0:0; 0:1; 1:0; 1:0.2; 1:1; 1:2; 0.2:1; and 2:1 ratios of Ca to P were fed to the soft-shelled prawn. Shell quality, survival and growth of prawn were observed biweekly. Prawn fed a diet with 1:1 Ca to P ratio (Diet 5) gave the best response in terms of weight gain (62%) and recovery from soft-shelling (89%). Soft-shelled prawn fed Ca-P-deficient diet did not improve in shell quality. Survival ranged from 50 to 100%, ans was significantly low with prawn fed the Ca- or P- deficient diets. The highest levels of both Ca and P occurred in the exoskeleton of normal prawn. The increased levels of these minerals in the exoskeleton in soft-shelled prawn indicated impaired mobilization of these mineral elements from the former to the latter for use in formation and hardening of shell.

No simple, well-accepted procedures exist for comparing the relative performance of genetic strains of fish in aquaculture environments. The major technical problem is providing adequate statistical replication of ponds or cages. Inclusion of an "internal reference" population of standard fish in each pond can reduce replicate error caused by variation in the physical environment, food supply and population density. This statistical procedure is feasible only if there is no biological interaction (interference competition) between the strain and the reference fish. An experimental design is described in which the replicates contain different proportions of reference fish relative to the test strains. This permits the effects of interstrain interference to be estimated. Data from growth of tilapia Oreochromis mossambicus in crowded aquaria are used to illustrate the effect of interference and other nonlinearities in the experimental design.

This paper reports an experimental design in which reference fish are included in each replicate to provide internal statistical control over environmental variation. Growth of 10 full-sib families from each of 3 strains of Oreochromis niloticus were compared in a crowded environment. A third strain of red tilapia was mass-spawned to provide reference fish. From each family, 25 equal-sized tilapia fry were matched with 25 equal-sized red tilapia fry and reared for 3 weeks in small floating cages inside a bigger tank. Growth of test strains were positively correlated with growth of the reference population. The 3 strains differed significantly in their growth rates. The reference fish technique is useful in experiments in ponds or cages, where variable environmental factors induce positive correlations between reference and test strains.

The midgut glands and ovaries of unablated and ablated females of Penaeus monodon were examined before and after spawning by light and electron microscopy to elucidate the role of the midgut gland during vitellogenesis. In addition, the larvae of both were divided into fed and starved groups and the mortalities were recorded up to stage postlarva 5 in order to compare the quality of the offspring from unablated and ablated spawners. Although a limited number of spawners was used in this preliminary study, a close interaction of the midgut gland and the ovary during vitellogenesis is evident. The influence of eyestalk ablation on the breeding success is discussed and hypothetically correlated to endocrinology. In late vitellogenesis, the resorptive cells of the midgut gland of an unablated female exhibited specific ultrastructural characteristics such as whirls of rough endoplasmic reticulum, conspicuous Golgi bodies and highly active smooth endoplasmic reticulum. The ablate these features only in moderate development. After spawning, the normal structures of the midgut gland cells were restored to a large extent. In the ovary of the unablated female before spawning, mature oocytes were dominant. After spawning, the ovary of the unablated female contained only immature oocytes. In contrast, all stages of maturation could be found in the ablated female 2h after spawning. The hatching rate was much lower in the ablated female. Up to stage postlarva 5, however, fed larvae from the ablated and unablated spawners had the same mortality rates. Starved zoea 1 from both types of spawners could not reach the next moulting stage without feeding. This indicates the urgent necessity of good feed at the very beginning of larval development. When the larvae were fed until moulting to mysis and then starved during mysis stage, the offspring of the ablated spawner died earlier than that of the unablated female. Only a very few starved larvae reached the postlarval stage. In any case, starvation led to an extension of the various larval stages and substages.

Studies on some aspects of tilapia and feed formulation conducted at BRS are reviewed in this paper. The effect fo varying dietary crude protien on growth and spawning frequency of tilapia was determined under laboratory conditions. The weight of male fish increased as dietary crude protein increased; however, weight gain of male fish did not follow a definite due to the asynchronous nature of spawning of the tilipia. Results suggested that when diets contain high-quality protein, and feedig is at station level, the influence of increasing dietary protein on spawning frequency and growth of the females are not cxonsiderable. In another study, tilapia broodstock in cages and tanks had the best growth and highest fry production when fed a 40% CP diet. Ipil-ipil leaf mal as a sole or major source of dietary protein caused weight loss among tilapia breeders, drastic reduction in fry production, and eventually cessation of reproduction. The growth of breeders describers decreased significantly with the incorpotion of more than 40% ipil-ipil in the diet. For Nile tilapia fry, growth was enhanced by availability of high phytoplankton densities in the rearing medium through the culture period. Feeding the fry with unialgal culture of Navicula and Chroococcus resulted in highest gains and survival rates. Chlorella gave poor survival and growth. Rice bran or Moina as feed for the fry was nutritionally inadequate. Their nutritional value improved when both were combined as feed.

Larval rearing of P.monodon requires mass culture of selected phytoplankton and zooplankton species. In the protozocal stage, Skelatonoma; Chaetoceros or Tetraselmis is given singly or in combination. The rotifer Brachionus and/or the brine shrimp ArTEMI are added to the diet as larvae metamorphose to the mysis stage. Attempts to replace these organisms with other organisms or with artificial diets are discussed. The use of microparticulate diets as supplement to algal food or Artema increases larval survival to 30-70%. The advantages of using this type of diet are enumerated.

Knowledge on nutritional requirements of prawn juveniles and broodstock are scanty. However, relatively more information is now available with regard to requirements of juveniles compared to that of broodstock. Many studies suggest the storage and utilization of lipids for maturation and spawning of P. monodon broodstock. Ovarian lipid increases more than twice at the start of maturation (Stage II) and reaches maximum at full maturity (Stage IV). Prawn juveniles require 40-45% protein, 5-10% lipid, and 20-25% carbohydrates. A protein-energy ratio of 120 mg prot/Kcal results in better growth and survival. The quality of protein and lipid is very important for both stages of the prawn. Eleven amino acids are essential but quantitative requirements have not been established. Likewise, amounts of essential fatty acids such as arachidonic, docosapentaenoic and eicosahexaenoic acids have yet to be defined. Cholesterol and lecithin are also necessary. Preliminary results of a 35-day feeding experiment showed that a vitamin free semipurified diet, choline-free and inositol-free diets significantly suppressed growth while niacin-free and pyridoxine-free diets provide for similar growth as that of a diet with all the vitamins present. Mineral needs have not been studied for P. monodon. Feedstuffs of good nutritive value in prawn grow out and broodstock diets are; fish meal, shrimp head meal, shrimp meal, mussel meat, Acetes sp. or "alamang", soybean meal, squid meal, earthworm meal, and annelids. In addition, cod liver oil, fish liver oil, soybean oil, and beef tallow have been used in varying proportions as sources of some essential fatty acids in practical diet development. Although there are practical diets that can be recommended, improvement of these diets will continue as new nutrient requirements are established.

In the Philppines, feeds and constitutes some 70% of the total capital cost in aquacultural, which illustrates the central ipmortance of such inputs and at the same time justifies a major research effort to study the field of nutrition, feeds, and feeding. Given a nutritionally adecquate food, it is necessary to examine whether environmental condition (e.g., water temperature, oxygen , etc.) allow fish to efficiently use the food for growth to ensure a profitable yield. If yioeld is as central to aquaculture as growth is to fish, then the improvement of fish yield in aquaculture should benefit from the fundamental understanding of environmental control of fish growth. In tropical aquaculture where high temperature are the outstanding characteristics, it is worth consideriing whether such temperatures favor efficient fish production. Since temperature increases the rate o metabolic processess in fish, the energetic cost of this elevated metabolic activity may be considered in competition with growth for a share of the energy derived from the food (Brett, 1979). These interacting factors of food (intake and ration) and temperature and their effects on fish growth should be thoroughly studied if an economicaly vaible management is desired. The present research project focussed on research (Lates calcarofer) aquaculture by using the bio-energetic concept following the models of weel studied species such as perch, Perca fluviatilis (Solomon & Brafield, 1972); sockeye salmon, Oncorhynchus nerka (Brett, 1979); brown trout, salmo trutta (Elliott, 1972; 1975a; 1975b; 1976; 1982), and the African catfish, clarias gariepinus (Hogendoorn, 1983; Machiels & Henken, 1986). This, being a long term goal connat be attained before basic variables will have been studied. The immediate aims of this research project era, therefore, (1) examination of feeding rates and food consumption of the seaperch in relation to body size and temperature, and (2) determination of growth rate in relation to temperature and ration size. This study will be conducted over a 3-years period. Firstly preliminary trials on feeding rates and food consumption by individual seaperch will be carried out to determine minimumand maximum rations. Subsequently experiments studying the relation between temperature, ration (starvation, maximum, minimum) and growth will be conducted. Variables and parameters to be investigated durig the experiment will concentrate on body size, body composition, composition of growth increment,tempereture and metabolism (oxygen consumption).

This review paper highlights counry reports presented at the Workshop on Asian Finfish Nutrition Sponsored by the International Development Research Center of Canada in 1983. Result of researches on the amino acid, lipid, mineral and vitamin requirements of some cultured finfishes in the larval, juvenile and broodstock stages are discussed. Complete essential amino acid requirements have been determined for common carp; only three have been qualified for tilapia. Many researches were conducted to replace trash fish and fish meal as protein source in fish diet. For O. niloticus, soybean meal can replace 50% of the fish meal in the grow-out diet. Essential fatty acids influence the dietary value of live food organisms for fish larvae. Rotifers cultured with yeast were low in W₃ highly unsaturated fatty acids while those grown in Chlorella were high in 20: 5W₃. Similarly, "lablab" showed higher W₃/W₆ ratio than "lumut". On the other hand, chemical, and Artemia from two sources showed that mineral is not the principal factor in the dietary value of natural feeds. Over-all, fundamental knowledge on the nutritional requirements of finfishes in the region is lacking.