Food choice by Cherax quadricarinatus was measured from video recordings of the time spent feeding on decayed plant material and zooplankton. Crayfish within the size range 20–75 mm spent a significantly longer time feeding on plant material, whilst crayfish at independent stage 1 (with yolk) did not spend a significantly different time at either of the two food types. Plant material, but not zooplankton, was often picked up to be consumed near or within shelters, which is consistent with ease of handling of plant material and with shelter dependence shown by redclaw crayfish.

Carpospore germination and early stages of development in Gracilaria edulis and Gracilaria rubra of the Philippines are described for the first time. Both species follow the "Dumontia type" or the immediate discal type of growth. Young plants with secondary branches were observed after 17 days of germination.

The reproductive performance of unilaterally eyestalk-ablated wild male Penaeus monodon was compared with that of unablated prawns (controls). After being stocked for 6 weeks in flow-through tanks, ablated males showed significantly higher sperm count (153.6 × 10⁶ vs.77.5 × 10⁶), less abnormal sperm (45.5% vs 73.3%), larger sperm head diameter (6.682 μm vs. 5.568 μm) and longer spike (5.096 μm vs. 4.360 μm) compared to unablated ones. Gonad index, spermatophore weight and percentage of live sperm were not significantly different between ablated and unablated males. No apparent decline in reproductive capacity was detected when comparing unablated prawns at the start of the study and after 6 weeks.

The milkfish, Chanos chanos Forsskal, industry in the Philippines suffers from a limited supply of wild fry. The demand for milkfish fry has spurred research in artificial propagation to supplement the natural seed supply. Spontaneous maturation and spawning of milkfish beginning at 5 years of rearing in floating net cages or concrete tanks coupled with improved egg collection technique have increased daily egg collection to a maximum of 3 million eggs and provided adequate volumes of eggs for mass fry production. Annual egg collection and number of spawnings were markedly higher in cage-reared stocks older than 9 years old than stocks less than 9 years old. Egg collection of tank-reared stocks were comparable to those collected in cages. As feed constitutes a major portion of the operating expenses for establishing and maintaining milkfish broodstock, further studies must be geared towards defining optimum dietary requirements and ration size for gonadal maturation and spawning. Also environmental manipulation studies must be conducted for year-round spawning. Developments in these areas should ensure the production of maximum numbers of high quality eggs and fry year-round.

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.