Juvenile and adult Artemia produced in a semi flow-through culture system were used as food for postlarval shrimp. The growth performance of shrimp reared on such ongrown Artemia live prey is identical to the growth obtained when feeding newly hatched Artemia. However, a significantly better stress resistance is obtained when the postlarvae are exposed to a low salinity in a stress test. Besides nutritional and energetic advantages, the use of Artemia biomass for feeding postlarval shrimp also results in improved economics as expenses for cysts and weaning diets can be reduced.

Agar is a high-priced phycocolloid usually extracted from red seaweeds (Rhodophyta). It has many uses in the food and pharmaceutical industry (Chapman 1970, Armisen and Galatas 1987). Worldwide production of agar has reached 5000t and the demand is still increasing because of new applications (Santelices and Doty 1989). In laboratory-scale extraction of agar the filtration system preferred is a stainless steel pressure filter (Aguilar-Santos and Doty 1978, Hoyle 1978). Commercial-scale extraction, however, uses filter presses of varying designs, each according to the particular need (Armisen and Galatas 1987). In small laboratories with limited facilities, an improvised extraction/filtration unit can be devised for routine laboratory work on agar processing. In the course of extraction/filtration trials conducted at SEAFDEC/AQD, a simple but efficient extraction/filtration unit was designed. It took into consideration the volume of the sample, the temperature during extraction, and the ease of using the unit.

Agar is a high priced phycocolloid extracted from red seaweeds (Rhodophyta) called agarophytes. It is a mixture of polysaccharides whose basic monomer is galactose (Armisen and Galatas 1987). Agar has many uses in the food and pharmaceutical industry, and the measure of its commercial value is based on its physical properties. One of the most important physical properties of commercial agar products is its gel strength (Chandrkrachang and Chinadit 1988). Gel strength is the force required to rupture the gel and it is measured through the use of gel testers available in the market, such as the Nikkan-sui, Rowerbal, and the Marine Colloids gel testers. Each instrument has built-in specifications for optimum use and results. Standard procedures used in the preparation of 1.5% agar gels for gel strength determination usually require 1.5 g of sample. Replication of samples in laboratory testing is however standard requirement and replication is constrained when sample extracts are scarce. This paper discusses the effects on gel strength of different gel depths and gel surface areas. It aims to identify the minimum size of vessel and depth of gel that will give optimum results using a Marine Colloids Model GT-2 gel tester.

Tiger shrimp (Penaeus monodon) juveniles were exposed to varying concentrations of rotenone and saponin to determine their effects on survival and shell quality. The highest concentrations tested, 50 ppm rotenone and 100 ppm saponin, were not lethal to shrimp. Shrimps exposed to 0.001 to 50 ppm rotenone had 7.4-66.6% shell softening while shrimps exposed to 0.001 to 100 ppm saponin had 2.66-66.6% shell softening. The shell softening rates were significantly higher in 1.0 to 50 ppm rotenone and 100 ppm saponin than in control shrimps.

The dietary requirements of juvenile milkfish (Chanos chanos Forsskal) for essential amino acids were determined in a series of experiments. The fish (< or = 8.0 g) were reared in fiber glass tanks provided with flow-through seawater at 28 degrees C and salinity of 32 g/L for 12 wk. In each experiment, a series of amino acid test diets was formulated containing a combination of intact protein sources (casein-gelatin, fish meal-gelatin, fish meal-soybean meal or fish meal-zein) and crystalline amino acids to simulate the levels found in milkfish tissue proteins except for the test amino acid. Each set of isonitrogenous diets contained 40-45% protein and graded levels of the amino acid to be tested. At the end of the feeding experiment, growth, survival and feed efficiency were determined. The requirement level for each essential amino acid was estimated from breakpoint analysis of the growth curve. The dietary essential amino acid requirements (as the percentage of dietary protein) of milkfish juveniles were as follows: arginine, 5.25; histidine, 2.00; isoleucine, 4.00; leucine, 5.11; lysine, 4.00; methionine, 2.50 (cystine, 0.75); phenylalanine, 4.22 (tyrosine, 1.00) or 2.80 (tyrosine, 2.67); threonine, 4.50; tryptophan, 0.60; valine, 3.55. This information is valuable in developing cost-effective practical or commercial feeds and research diets for milkfish juveniles.

Hydrogen sulphide is a toxicant naturally produced in hypoxic marine sediments, hydrocarbon and brine seeps and hydrothermal vents. The California killifish, a salt marsh resident, is remarkably tolerant of sulphide. The 50% lethal concentration is 700 μM total sulphide in 96 h, and 5 mM in 8 h (determined in flow-through, oxygenated sea water). Killifish exposed to sulphide produce thiosulphate which accumulates in the blood. The cytochrome c oxidase (a major site of toxicity) of the killifish is 50% inhibited by <1 μM sulphide. Killifish liver mitochondria are poisoned by 50–75 μM sulphide but can oxidize 10–20 μM sulphide to thiosulphate. Sulphide causes sulphhaemoglobin formation (and impairment of oxygen transport) at 1–5 mM in vitro and to a small extent at 2 mM in vivo. Killifish blood neither catalyses sulphide oxidation significantly nor binds sulphide at environmental (low) sulphide concentrations. Exposure to 200 μM and 700 μM sulphide over several days causes significant increases in lactate concentrations, indicating shift to anaerobic glycolysis. However, individuals with the most lactate die. In terms of diffusible H2S, the killifish can withstand concentrations two to three orders of magnitude greater than would poison cytochrome c oxidase. The high sulphide tolerance of the killifish, particularly of concentrations typical of salt marshes, can be explained chiefly by mitochondrial sulphide oxidation. Sulphide tolerance and mitochondrial sulphide oxidation in the killifish have a constitutive basis, i.e. do not diminish in fish held in the laboratory in sulphide-free water for 1–2 months, and are improved by prior acclimation.

The thyroid hormone levels in female rabbitfish, Siganus guttatus, plasma, eggs, and yolk-sac larvae were measured before and after thyroxine (T₄) injection in female spawners at doses of 1, 10, and 100 μg T₄/g body weight (BW) fish. T₄ and triiodothyronine (T₃) levels in maternal plasma, eggs, and yolk-sac larvae were elevated following T₄ administration. Apparently, there is conversion of T₄ into T₃ in the broodfish which suggests the presence of the enzyme, 5′-monodeiodinase, in rabbitfish. T₄ and T₃ in maternal circulation were easily transferred into the oocytes and subsequently into the larvae. Larvae from spawners treated with 10 and 100 μg T₄/g BW tended to be longer and showed sornewhat better survival compared to the control and those injected with 1 μg T₄/g BW 7 days after hatching. These findings suggest that thyroid hormones may play an important role during early larval development of rabbitfish.

Egg cannibalism by milkfish spawners in a circular floating net cage was investigated. The cage was lined with a fine mesh hapa net to retain spawned eggs and to prevent the entry of fish egg predators. Water samples were collected from the surface (0 m), middle (1.5 m), and bottom (3.0 m) of a 10 m diameter by 3 m deep floating net cage at the time of initial detection of spawning (0 min) and at 30, 60, 120 and 240 min thereafter. The mean number of spawned eggs at the surface significantly decreased (P<0.05) 60 min after spawning and very few eggs were recovered 240 min later. There was no significant difference (P>0.05) in the mean number of spawned eggs collected from the middle and bottom of the net cage at various times after spawning. Eggs were found in the digestive tract of all milkfish sampled (n=6) at about 5 h after spawning, indicating that captive milkfish eat their own eggs. It is recommended that spontaneously spawned milkfish eggs should be collected immediately after spawning to avoid loss by egg cannibalism.

Three experiments were conducted to determine the effects of a simultaneous injection of varying doses of luteinizing hormone-releasing hormone analogue (LHRHa; 0.005–0.10 μg)/body weight (BW) in combination with a fixed dose of pimozide (PIM; 1 μg)/g BW on oocyte maturation and ovulation in the catfish Clarias macrocephalus (body weight: 39 to 167 g). This was done by monitoring the development and size of the oocytes after hormone injection at various sampling intervals for 48 hours. In Experiment I (March 1989), only the fish injected with 0.10 μg LHRHa + 1μg PIM/g BW underwent final maturation and ovulation. However, oocyte maturation and ovulation were observed in all treated fish in Experiment II (April 1989). Oocyte maturation and ovulation were also induced except in fish injected with the lower dose combination (0.005 μg LHRHa + 1 μg PIM/g BW) or PIM alone (1 μg/g BW) in Experiment III (September 1989). No maturation was observed in all vehicle-injected control fish in the three experiments. Mean egg diameter of fish that were induced to mature increased during ovulation but remained similar in size in fish which did not undergo final maturation. This study showed that captive C. macrocephalus can be induced to undergo oocyte maturation and ovulation at 15 to 16 h after a simultaneous injection of 0.01 to 0.10 μg LHRHa + 1 μg PIM/g BW.

The effect of cysteine concentration and cysteine source [cysteine, methionine or 2-oxo-thiazolidine-4-carboxylate (OTC)] on the metabolism of [35S]cysteine was studied in isolated rat hepatocytes. Production of each of the major metabolites of cysteine (glutathione, sulfate, taurine) increased as cysteine or methionine, but not OTC, concentration in the medium was increased. At equimolar exogenous substrate concentrations, cysteine availability to hepatocytes was greater from exogenous cysteine than from methionine, and that from methionine was greater than from OTC. The partitioning of cysteine, or the percentage of total metabolism resulting in production of each of the major metabolites, was markedly affected by cysteine concentration or availability. Low cysteine availability favored its utilization for glutathione; high cysteine availability favored its catabolism to sulfate and taurine. Under conditions of low cysteine availability (incubations with 0.2 mmol/L OTC), glutathione, sulfate and taurine production accounted for 90, 10 and 1%, respectively, of total metabolism. Under conditions of high cysteine availability (incubations with 1 mmol/L cysteine + bathocuproine disulfonate), glutathione, sulfate and taurine production accounted for 19, 47 and 34%, respectively, of total metabolism. Cysteine supplied as such and cysteine formed intracellularly from methionine were similarly partitioned. These studies demonstrate that methionine is not a superior substrate to cysteine for hepatic glutathione synthesis and that cysteine concentration (presumably intracellular cysteine concentration) has a major effect on the partitioning of cysteine sulfur to taurine in rat hepatocytes.