A method for the separation and cryopreservation of Brachionus plicatilis embryos is described. Juveniles with uniform development were collected from a cultured stock by passing them through a series of nets. Collected juveniles were cultured and the embryos separated by vigorous vortex mixing as soon as the majority had laid their first eggs. Separated embryos at stage I (cleavage stage), stage II (invagination stage), stage III (symmetrical embryo stage), or stage IV (“eyed” stage) were frozen to −196°C using various concentrations of DMSO and a two-step freezing procedure. No stage I embryos survived freezing and the highest post-thaw survival was obtained with stage III embryos. A DMSO concentration of 10% of the freezing medium resulted in high post-thaw survival while concentrations higher than 10% appeared to be harmful to embryos. Prolonged incubation in 10% DMSO for up to 30 min before freezing increased post-thaw survival. Incorporating the above results, stage III embryos from a single batch culture were incubated in 10% DMSO for 30 min and frozen to −196°C. Post-thaw survival rates of 63%, 62%, 53%, and 55% were obtained after 3, 7, 15, and 30 days of storage in liquid nitrogen, respectively. Survivors fed actively on marine chlorella and started to lay eggs 2–3 days after thawing.

In aquaculture research, maintenance of water culture quality is of great importance. Recent improvement in fishpond management and fish culture systems, such as intensive feeding and fertilization, have created complex problems. Deterrioration of weter quality is primarily the resulting effect of these improvements. Foe example, high-protein feeds and nitrogen fertilizers applied in fishponds produce considerable amount of nitrate in the water. Moreover, their synergistic effects cannot be ignored. Hence the routine determination of nitrite in fishpond water is required. Since its introduction by Small et al., ion chromatography has been widely used for the determination of ions in water. However,the presence of very high concentrations of chloride is the main obstacles in the analysis of seawater samples, affecting the separation and detection not only of nitrite but also of other anions. Itoh and Shinbori applied ion chromatography to the analysis of seawater using a 125-cm long column and a conductimetric detector. This technique provided by a simple and sensitive analysial method for brine samples. However, nitrite could not be determined owing to the presence of a large chloride peak. Attempts to determine nitrite in seawater also led to innovations in the methodology. Lee and Field employeed a post-column cerium flourescence detection system to determine nitrite and nitrite in drinking water and seawater. The use of a pretreatment column in the silver form for removal of chloride has been reported. Various detectors have been applied in ion chromatography in addition to the conductimetric detector. The UV detector has been shown to be luseful detector for several kinds of inorganic anions. Selected detection of specified inorganic ions can be achieved by tuning the wavelength of the UV detector in ion chromatography and also in ion-exclusion chromatography. The elemination of the chloride matrix interference in the sub-ppm determination of nitrite in seawater was achieved by a heart-cutting and recycling method using a dual detection system consisting of conductimetric and UV detectors. This method, however, requires valve switching during analysis and needs a long analysis time. This paper describes a simple and rapid method of UV-absorbing anions, such as nitrite, nitrite and bromide, in brine samples using a chloride-form anion-exchange resin column combined with a UV detector.

Six semipurified diets comprising three levels of protein (25, 35, 45% of dry matter) each at two levels of estimated energy (3161, 3832 kcal/kg) were fed to fry for 8 weeks in 250-l tanks at a stocking density of 80 fish/tank. Growth increased with increasing dietary protein \((P\lt0.01)\) and energy \((P\lt0.05)\). Within isocaloric diets, a positive correlation was found between growth and dietary protein-to-energy \(\left(\frac{P}{E}\right)\) ratio \((P\lt0.05)\). Protein productive value (PPV) and protein efficiency ratio (PER) were negatively correlated with dietary \(\left(\frac{P}{E}\right)\) ratio. The equations describing this trend were: \(\mathsf{PPV}=50.16-0.19X\) and \(\mathsf{PER}=2.83-0.12X\), where \(X\) is \(\left(\frac{P}{E}\right)\). Based on responses for growth rate and efficiency of protein utilization, a diet with 35% protein and 3832 kcal/kg energy was found to be best for rabbitfish fry. Carcass fat levels increased in those fish fed diets with 3832 kcal/kg energy. Carcass protein and ash percentages remained essentially constant and independent of dietary treatment.

Tissues (hepatopancreas, muscle, gonad) of wild Penacus mordon females with ovaries in different stages of development and males were analyzed for Upid content and fatty acid composition. Hepatopancreatic tissue had the highest mean levels of lipid at 15.72–25.20% in females and averaged 46.20 ± 1.53% in males. Levels of Lipid in the muscle were low with no marked variation throughout the maturation s-es. Ovarian lipid levels increased significantly at stage II (early maturing ovaries) and remained high through stage IV (fully mature ovaries). Peak lipid level was found at stage III (late maturing ovaries) and coincided with a decline in hepatopancreas lipid. Ovarian and hepatopancreatic lipids declined drastically in spent females. Profiles of fatty acid in the tissues consistently showed the presence of PUFA 204n-6, 20:5n-3 and 22611-3, with high levels in the polar lipid fraction of vitellogenic ovaries. These values were reflected in the male testis and spawned eggs. The finding suggest storage and utilization of lipids for maturation and spawning processes and that the phospholipids were mainly responsible for increases in ovarian lipids. The type of fatty acids present in maturing prawn ovaries is indicative of their importance in reproductive physiology.

Larval mortalities associated with luminescence have been observed in epizootic proportions in black tiger prawn (Penaeus monodon) hatcheries in Panay Island, Philippines. Luminescent vibrios, identified as Vibrio harveyi and V. splendidus, were isolated from infected larvae but not from uninfected ones. These bacteria were also recovered readily from seawater samples from nearshore areas, the main source of hatchery rearing water. Thus, it is possible that the nearshore seawater is one major source of infection. Pathogenicity tests resulted in significant mortalities of larvae and postlarvae of P. monodon within 48 h of immersion challenge. Scanning electron microscopic observations show that colonization by the bacteria occurred specifically on the feeding apparatus and oral cavity of the larvae, suggesting an oral route of entry for the initiation of infection.

The amount of rotifers consumed by a single sea bass Lates calcarifer larva per day (R) was examined by both the direct and by the satiation-digestion methods. In the direct method, R is estimated by the number of rotifers left in the larval tanks and larval density in the tanks, while in the satiation-digestion method R is estimated by the amount of rotifers found in the digestive tract of the larvae. In both methods, the amount of rotifers consumed by the larvae increased exponentially with larval growth. The relationship between the total length (TL) and the log-log plots of the maximum amount of rotifers eaten by a larva can be expressed by the following equations; \(R=1.799 \times TL^{4.398} (r=0.975)\) for the direct method and \(R = 4.861 \times TL^{3.432} (r = 0.907)\) for the satiation-digestion method. The relationship between TL and body wet weight (BW) can be expressed as: \(BW = 2.607 \times 10^{-4} \times TL^{3.786} (r=0.960)\) for larvae smaller than 6.5 mm TL and \(BW = 15.053 \times 10^{-3} \times TL^{2.855} (r = 0.916)\) for those larger than 6.5 mm TL. The index of satiation was almost the same for day 6(0-6), D-9 and D-12 (8.3-23%), higher range was observed in D-15 larvae. The index of daily feeding amount was comparatively higher in D-12 larvae compared to D-6, D-9 or D-15 larvae.

Mature female sea bass (Lates calcarifer Bloch) were injected once intramuscularly with 20 μg luteinizing hormone-releasing hormone analogue (D-Ala⁶, Pro⁹-LHRH-ethylamide) per kg body weight (BW) at different times of the day. Following hormone injection, the incidence of initial spawning and the number of eggs spawned by each fish were recorded. Saline-injected fish did not spawn. Fish spawned at dawn or 33.7–40 h after an LHRHa injection at either 11.00 h or 17.00 h. When LHRHa was administered at 23.00 h or 05.00 h, sea bass spawned during the day or at 38–47.3 h post-injection. Mean egg production levels of 26.8–34.4 × 10⁴ per kg BW were higher for fish which spawned at dawn. Low mean egg production levels (6.2–19.9 × 10⁴ eggs per kg BW) were observed when LHRHa-injected fish spawned during the day. These results demonstrate that the time of initial occurrence of spawning varied with the time of day that LHRHa was administered and that the number of eggs shed was influenced by the time of day that hormone-induced sea bass spawned.

Hatchery-bred larvae of three marine fish species, milkfish (Chanos chanos), seabass (Lates calcarifer) and rabbitfish (Siganus guttatus) were reared on rotifers and Artemia nauplii. Development of the mouth width and larval growth were monitored in the laboratory. Growth was slow on the first six days in milkfish and rabbitfish and on the first four days in seabass. Mouth width at opening was the smallest in rabbitfish (90-110 μm), followed by seabass (170-220) μm) and milkfish (180-270 μm), and the mouth width at the time when the larvae began to eat rotifers was 219 + 7.4 μm, at 82.5 h after hatching, in rabbitfish, 224 +7.9 μm, at 71 h, in seabass, and 3306 + 38.9 μm, at 125 h, in milkfish. A positive correlation between mouth width and larval growth was shown by three species studied.

An ion chromatographic method for separating and detecting anions in brine samples is described. Nitrite, bromide, nitrate, and sulfate ions in brine samples are well separated when chloride ion concentration in the sample solution is below 2000 ppm. However, at higher chloride concentrations, nitrite and chloride peaks are not resolved. Low level nitrite ion in the brine sample is separated from a major chloride ion by a heart-cutting and recycling system. After elution, the unresolved portion, including the nitrite ion, is cut and trapped in a 10-mL sample collecting loop and reinjected on the column by using 6- and 4-port valve systems. The detection limit of nitrite spiked in the seawater samples is 0.5 ppm.

Annual changes in the ovarian development and serum vitellogenin concentration were investigated in the river sculpin, Cottus hangiongensis, sampled monthly from a river in southern Hokkaido, Japan. Ovarian development started advancing from summer and continued during the winter months until March with a maximum mean gonadosomatic index (GSI) of 15.99%. Hepatosomatic index (HSI) was also highest in March with a range of 5.13-5.95%. Spawning season usually occured from April to May. Annual changes in serum vitellogenin level correlated very well with the patterns of GSI and HSI, as well as histological changes of the ovary. However, high serum vitellogenin was maintained in March and April.