Cryopreserevation of different strains of Brachionus plicatilis symmetrical stage embryos was conducted. One S-type strain, namely Yashima-S (YS), and three L-type strains, namely Yashima-L (YL), Nagasaki (NG), and Hamana (HA), were used. Symmetrical stage embryos in 10% DMSO-28‰ sea water solution were frozen at -196°C using a two-step freezing procedure; the embryos were first cooled slowly from -5°C to -20°C at a rate of 0.3°C/min and then cooled rapidly by direct transfer to liquid nitrogen. Frozen samples were thawed in a gently stirred water bath at room temperature. A mean survival rate of 36% after 30 days storage in liquid nitrogen of HA strain was significantly lower than YS (55%), YL (58%), and NG (54%), and is due likely to its relatively larger embryo volume. There was no significant difference in the intrinsic rate of increase (r) between strains among clones taken from the cryopreservation or unfrozen control group. The results also indicate that various strains of B. plicatilis embryos can be cryopreserve without seriously altering their reproductive capability. The freezing method described could be of great potential in aquaculture and in future studies on rotifer genetics.

Effects of unilateral eyestalk ablation on wild and pond-reared Penaeus monodon during ovarian maturation were determined by examining the growth (e.g., carapace length, body length, body weight) and reproductive (e.g., gonad weight, gonadosomatic index (GSI), average and maximum oocyte diameter) parameters to compare their reproductive potential. Growth parameters were similar in the wild unablated and wild ablated prawns from the immature or previtellogenic (P) to mature or cortical rod (C) stages but increased during the immature (P) to maturing or vitellogenic (V) stages in the pond ablated prawns. During stage C, gonad weight was highest in the wild unablated group while GSI, average and maximum oocyte diameter was similar in the three groups. After spawning (stage S), gonad weight was similar in all groups but GSI, average and maximum oocyte diameter were higher in the pond ablated prawns than in the wild unablated and wild ablated groups. Changes in growth and reproductive parameters at various stages of maturation suggest that reproductive performance successively decreased in the wild unablated, wild ablated and pond ablated P. monodon.

The effects of supplemental feeding on milkfish growth, production, survival, water quality, and economic benefits in brackishwater ponds were evaluated by comparing a rice bran diet, containing 11.3% protein, and two pelleted diets, containing 22.0% and 27.4% protein, with an unfed control. Four 800-m² tide-fed ponds, subdivided into quarters, were used. Each treatment was replicated in four random pond compartments. Milkfish with initial average weight of 1 g were stocked at 8000/ha and feeding commenced when the average weight and standing crop were 57 g and 417 kg/ha, respectively. All supplemental feeds significantly (P<0.05) increased growth and production over the unfed control. Feeding diets containing 22.0% and 27.4% protein resulted in 35.3% and 46.7% higher net profits, respectively, whereas feeding rice bran resulted in a 34.4% lower net profit when compared to the unfed control. The growth of milkfish became significantly slower (P<0.01) than those fed the 27.4% protein diets when the standing crop of unfed and rice bran-fed fish reached 535 kg/ha and fish fed the 22.0% protein diet reached 972 kg/ha. Survival was not significantly different among the treatments. The concentration of metabolites in the culture water for all treatments was low but a significant increase (P<0.05) in level of total carbon dioxide and nitrite-nitrogen was observed as biomass increased.

The study was undertaken to determine the effect of 0, 25, 50 and 75% replacement of organic matter in the feed with rice straw compost on milkfish (Chanos chanos) growth and production. Treatments have similar organic matter and nitrogen loads. Up to 50% substitution (Treatments 1 to 3) was possible without significantly affecting fish growth and yield (668–725 kg/ha). A significant reduction in growth and yield (456 kg/ha) with 75% substitution (Treatment 4) implies that organic matter from compost did not contribute much to fish growth. Low phosphorus content of compost and inadequate phosphorus load in spite of increasing mineral input from compost resulted in similar primary productivity in all treatments. It appeared that compost was not a satisfactory feed substitute and that the fish derived most of their nutrition from the feed. The results further suggest that yield could be economically increased by using a low protein diet (23.8%) given at a lower rate (1.75% of body weight). To further improve yield, feeding rate can be gradually increased as biomass increases, although the most cost-effective ration will depend on the fish capacity to grow under certain environmental conditions.

Yields of Penaeus monodon Fabricius in brackishwater earthen ponds were determined using different fertilizer combinations in two sets of experiments. Results indicated that the use of fertilizers was vitally needed to sustain growth of shrimps at a stocking density of 5000 individuals/ha. Application of urea (45-0-0) and diammonium phosphate (18-46-0) fertilizers at nitrogen to phosphorus fertilizer rates (N:P₂O₅) of 15:15 and 30:15 kg/ha, together with 1 t/ha of chicken manure, was inexpensive and resulted in better yields. In another experiment, increase in the amount of nitrogen and phosphorus fertilizers did not significantly improve prawn yields, but did increase the cost of production. Different salinity levels affected survival in both experiments.

A feeding experiment was conducted to determine the effect of a commercial growth promoter, Bayo-n-ox, on Nile tilapia fingerlings (mean initial weight 3.6 g). After 6 weeks, the weight gain of fish given 25 mg Bayo-n-ox/kg body weight was somewhat higher than that of the control fish. A slight growth depression was manifested by fish given 50 mg Bayo-n-ox/kg body weight. Total length followed a trend similar to that of weight gain. However, growth, the feed conversion ratio and the survival rate were not significantly different (p > 0.05) among treatments.

Bighead carp (10.5 months old) stocked in cages in Laguna de Bay were assigned the following feeding treatments: 1. 40% protein diet, 2. 20% protein diet, and 3. no artificial diet (control), to determine the effects of feeding on growth and reproduction. The fish were fed for 15 months. Growth was monitored for the first 9 months and fish were induced to spawn in the succeeding months. Both weight gain and increase in total length did not differ significantly (P > 0.05) among treatments. Results of the induced spawning showed that fish fed the 40%-protein diet had the highest mean total weight of eggs/female, total number of eggs/spawning, and number of eggs/kg body weight. Fish fed the 20%-protein diet had intermediate values while the control fish had the lowest values for the same parameters. However, mean fertilization rates (54–58%) and hatching rates (61–78%) were not significantly different (P > 0.05) among treatments. The mean number of 3-day old fry of fish fed the 20%-protein diet (48 085) was lower than that of fish fed the 40%-protein diet (86 806). The control fish gave a significantly low (P < 0.05) number of 3-day old fry (37 469). When deprived of food for up to 10 days, fry of the fed broodstock had a lower mortality rate than fry of the control fish.

The importance of the analysis of low level nitrite concentrations in aqueous samples is increasing in various fields such as environmental, food, and aquaculture chemistry. Recent progress in ion chromatography paved the way to the direct analysis of nitrite in water samples at ppm to sub ppb levels. However, analysis of low level nitrite in highly concentrated salt matrix still remains a difficult problem. The presence of a large amount of the matrix ion makes establishment of an ion exchange equilibrium very difficult in the column, often resulting in bad peak shapes [1]. In previous papers, we reported the analysis of a nitrite and other anions in chloride matrix on a conventional low capacity anion-exchange column by means of a heart-cut and recycling method [1] and by using a potassium chloride eluent [2]. To monitor the nitrite peak, both a UV detector and a conductimetric detector has been used [3]. Several groups have demonstrated the potential of an electrochemical detector for a specific and sensitive detection of nitrate. [4-6]. Poly(vinyl alcohol) (PVA) gel have been introduced recently as a chemically stable HPLC column packings [7-9]. It was found that when an acidic eluent was employed, a PVA gel and its acylated gel columns produced large capacity factors for nitrite [10].

Penaeus japonicus nauplii from wild spawners were reared up to the early postlarval stage (PL20) in 12-t concrete tanks. A survival rate of 13-15% was obtained. Hatchery-reared postlarvae were restocked in concrete tanks for grow-out. After six months, survival rate was 49.3% with mean body weight of 20 g and carapace length of 21-33 mm. Ablated and unablated females were stocked together with males at 1:1 sex ratio in broodstock tanks. After three months, 11% of the ablated prawns spawned whereas 1.4% of unablated females spawned after five months. Nauplii from these spawnings were reared up to the adult stage thus completing the life cycle of J. japonicus in captivity.

The relationship of predator size to maximum prey size, and predator weight to weight of prey consumed among cannibalistic sea bass (Lates calcarifer Bloch) in a hatchery were assessed. Maximum prey size was computed from morphological measurements (predator mouth width, prey body depth and fish total length), while prey consumption was determined from predators kept in experimental beakers and fed only prey sea bass for a 7-day period. Maximum prey size was 61–67 % of predator total length \((TL_{prey} = 0.5944 TL_{predator} + 0.0724)\). Gut dissection of predators showed that size of ingested prey increased with increasing predator size not exceeding the maximum size limit indicated by the above equation. Daily prey consumption of predators in the beakers was expressed as \(W_{Prey} = -0.2407\; W_{predator^{2}}+ 0.7697W_{predator}-0.1141\). During hatchery rearing of sea bass, fish with length differences of more than 33 % must be separated and food of appropriate size provided to limit cannibalism.