Six different diets, commonly used in the Philippines for rearing milkfish, Chanos chanos, try, were tested by means of growth, survival and histology. These diets included: a) live food (Artemia nauplii); b) two different dry feeds; c) natural feed supplements (rice bran, egg yolk); d) a mixture of live and dry feeds. The mixed diet was found to give the best results, closely followed by live food. The dietary value of one of both artificial feeds improved with increasing age of the fish, whereas the other was clearly inadequate. The same was true for the natural compounds. Results obtained from statistical and histological analyses were congruent; the latter provided additional insights not obtained with statistic data alone.

To determine the effects of deficiency of individual amino acids believed to be essential to Penaeus monodon juveniles, a 28-day feeding experiment was carried out with P. monodon postlarvae. P. monodon postlarvae weighing around 120 mg each were randomly distributed in individual perforated one liter jars, 10 jars in 60-liter, fiberglass tanks, in a flow through seawater system, which passed through a 0.35 micron filter before use. Animals were reared in these jars for 28 days on semi-purified moist diets. Salinity and temperature ranged from 27 to 32 ppt and 26 to 28.9°C, respectively. Percentage weight gains and survival rates were not significantly different among test diets. However, some amino acids seemed to be more critical than others in the diets. Animals given phenylalanine-free, leucine-free, and methionine-free diets gained more than 300% compared to those fed the complete amino acid diets. A low weight gain of 228.6% was observed in animals fed arginine-free diet. Animals fed the histidine-free, lysine-free, threonine-free and valine-free diets also gained less than 200%. Survival rates were 60% for those given threonine-free and isoleucine-free diets, 70% for histidine-free and complete amino acid diets, whereas those fed the phenylalanine-free, leucine-free and methionine-free diets had survival of 80 to 85%. These results suggest the possibility that some amino acids were taken from sources outside the diets and could have corne from whatever bacterial growth there was in the rearing jars.

Acclimated milkfish fry (mean wet weight, 6.0 mg) were fed with unialgal cultures of five species of freshwater algae: Oscillatoria quadripunctulata, Chroococcus dispersus, Navicula notha, Euglena elongata and Chlorella ellipsoidea. In the first experiment, the filamentous blue-green alga, Oscillatoria, appeared most acceptable to milkfish fry throughout the growing period, while feeding milkfish fry with the unicellular species, Chroococcus, resulted in lower weights and survival. In the second experiment, increases in weight of milkfish fry fed with Oscillatoria alone or in combination with Chroococcus were comparable. However, a significant increase in survival was obtained with the combination feeding. A third experiment showed that high density cultures of Oscillatoria resulted in significantly large weight increments in all growth stages. The other algae tested did not support growth of milkfish fry. ¹⁴C-Labeled algae of the same species were fed to milkfish fry. Significantly high assimilation retes were observed in almost all growth stages of milkfish fry with Oscillatoria alone or Chroococcus alone. Negligible amounts of Navicula, Chlorella and Euglena were assimilated.

Sarotherodon niloticus with average weight of 28.42 ± 1.87g were immunized with formalin-killed Edwardsiella tarda using the hyperosmotic infiltration method. Test fish maintained in 30 l aquaria were grouped into four treatments. Group 1 and 2 were exposed to a single hyperosmotic treatment on day 0. Group 1 was bled on day 14 and group 2 was bled on day 28. Group 3 was given hyperosmotic treatments twice: on day 0 and day 14 and bled on day 28. Group 4 was an untreated control bled on day 28. All sera were analyzed for agglutinating antibody titer against E. tarda flagellar and somatic antigens. Results showed that flagellar and somatic agglutinin titers in all treatments were not statistically significant. Likewise, infection experiments where test fish were challenged with intraperitoneal injection of the test bacterium showed that the vaccination experiment did not effectively protect the test fish from infection by Edwardsiella tarda.

Three groups of immature seaperch acclimated in the laboratory on a mixed commercial pellet and minced trashfish diet were starved for 30 days. Thereafter, the first group was starved for 7 more days, the second was refed with commercial pellets, and the third with trashfish. Through transmission electron microscopy, it was found that after the acclimation period the hepatocytes of Lates calcarifer were primarily lipid-storing. Upon starvation, the following modifications in the hepatocytes were evident: decrease of lipid reserves, hepatocyte shrinkage, mitochondrial swelling, dilation of the cisternae of the rough endoplasmic reticulum (RER), and the presence of lysosomes. Among the refed fish, only the hepatocytes of those which were given trashfish recovered from the injury. Recovery was indicated by the restitution of the morphology of the mitochondria, development of parallel stacks of RER, increase in lipid and glycogen, and the distinct compartition of the hepatocytes.

Midgut gland cells of Penaeus monodon postlarvae were investigated by electron microscopy after starvation and refeeding with different diets. Well nourished postlarvae could be starved for 5 days without irreversible detriment. They recovered easily on a good diet. Only R cells were affected by a short starvation period. After 13 days of food deprivation the structures of all cell types were disintegrated. The postlarvae were able to starve for a maximum of 15 days. The most diversified ultrastructure was obtained by refeeding with cod liver oil and 2s (mixed diet). Casein was not well utilized. Sucrose was the poorest diet. The midgut gland of Penaeus monodon seems to be lipid oriented. Only fat was used as storage material; glycogen was lacking. Different ultrastructures were induced in R cells by a given diet after longer starvation periods. The reestablishment of their ultrastructure by means of a definite diet seems to be impossible after a certain period of starvation (point of no return). R cells are very sensitive to different diets. B cells show slight reactions, while F and E cells remain relatively unchanged. This indicates that R cells could be used to monitor the nutritional value of prawn diets in aquaculture.

P. viridis were exposed to 3.6 ppb, and 100 ppb mercury. The mussels were also fed with algae that had been precontaminated with mercuric acetate to give a final mercury concentration of 10 ppb. Mercury bioaccumulation appears to be a function of time and concentration and is manifestly enhanced by the presence of mercury-contaminated food organisms. The pattern of mercury tissue distribution after 30 days exposure was found to be as follows: gills > visceral mass > mantle. Depuration is a slow process. The animals failed to purge themselves of the total amount accumulated in 45 days. Smaller mussels were observed to accumulate mercury faster than the larger ones. The Tolerance Limit Test (TLm) showed a mean mercury tissue concentration of 9,890 ppb wetweight after 65 hours exposure to 1.0 mu g Hg mL^-1.

Pure cultures of the fungus Haliphthoros philippinensis isolated from infected Penaeus monodon larvae were exposed for 24 h to varying concentrations of the antifungal agents Benlate, calcium hypochlorite, clotrimazole, copper sulphate, Daconil, formalin, Fungitox, Furanace, griseofulvin, hydrogen peroxide, malachite green, Mysteclin C, phenol, potassium permanganate, Resiguard, Tide, tolnaftate and Treflan. The efficiency of each compound in inhibiting sporulation and mycelial growth of the fungus was measured. The results establish mycostatic and mycocidal levels for each fungicide.

Post-yolk-sac larvae of milkfish, Chanos chanos (commonly referred to as “fry”) were collected along the shore in the Philippines. Treatment of these long, slender and transparent larvae with L-thyroxine-sodium (Eltroxin, Glaxo) by immersion in 0.5 ppm solution (changed daily) markedly accelerated their growth and development. By day 15 of the treatment, the treated larvae had become silvery, opaque and adult-like in form, whereas the control larvae were still slender and transparent (or at best translucent) with incomplete silvering of the body. 0.1 ppm thyroxine was less effective. Discontinuation of the treatment after 8 days was also less effective as judged by the appearance and weight of the larvae on day 15.

Females of Siganus guttatus reared to sexual maturity in canvas tanks were induced to spawn by using human chorionic gonadotropin (HCG, Ayerst) at 500 IU/fish or about 2 IU/g body weight. The amount of HCG used depended on the initial mean egg diameter; the smaller the diameter, the more HCG was used. Fish with oocytes characterized by germinal vesicle migration (mean egg diameter ≥ 0.47 mm) spawned without HCG injection. Fertilization and hatching rates for both treated and untreated fish were more than 90%. The larvae were reared to metamorphosis using rotifers from day 2–17, rotifers + newly hatched Artemia nauplii from day 18–20 and rotifers + newly hatched Artemia nauplii + artificial feed from day 21–35. In addition, Isochrysis galbana was introduced to the rearing tanks from day 1–10 and Chlorella sp. and/or Tetraselmis sp. from day 1–35. Survival rates of larvae tended to be lower as the broodstock became older.