Some aspects in early life stage of siamese gourami, Trichogaster pectoralis (Regan) larvae

Size at sexual maturity of female Siamese gourami was 18.07+-1.10 cm (mean+-SD) in average total length and 94.20+-13.39 g in average body weight. The fecundity was 26,261+-5,215.81 ova/fish and gonadosomatic index (GSI) was 10.9+-2.1 percent. Newly hatched larvae of Siamese gourami were produced by induced spawning using chemical injection (Suprefact and Motilium). The sexually mature fishes were cultured in fiber-glass tank (water volume 300 liters) with the ratio of male and female brooders 1:1. The fertilization rate, hatching out and hatching rate experiments were carried out using a 15-liter aquarium (water volume 10 liters) containing 1,000 eggs. The eggs were floating and rounded. The fertilized eggs had a diameter of 908.25+-39.13 micro m. The average fertilization rate was 91.12 percent, hatching out was 22 hr 10 min and average hatching rate was 83.03 percent at a water temperature of 27.0+-30.5 deg C. Sampling of the newly-hatched larvae was done at 2-hour intervals, when 20 of them were randomly taken and preserved in 10 percent buffered formalin for later analysis to determine the time of final yolk absorption. Observation using a microscope revealed that newly hatched larvae were 2.73+-0.02 mm in total length and had yolk sacs of 153.76+-2.49 micro cubic m in volume. The yolk sacs were completely absorbed within 110 hr after hatching at a water temperature of 27.0-30.5 deg C. Up until full mouth development (start of feeding), 2-hourly samplings of twenty newly hatched larvae were taken from an aquarium for observation of the size of mouth opening. All the larvae had open mouths about 60 hr after hatching (3.56+-0.04 mm TL), with the mouths measuring 443.64+-24.26 micro m in height. The feeding experiments were carried out using a 15-liter glass aquarium (water volume 10 liters) containing 1,000 larvae aged 1.5 days post-hatching (just before the mouth opened). They were fed with rotifer at a density of 10 ind/ml. Twenty larvae were collected at random from the aquarium at 2-hourly intervals, preserved in 10 percent buffered formalin, and then dissected to determine the presence of rotifer in the digestive tract. The digestive tracts were fixed at 72 hr of hatching at water temperatures of 27.0-30.5 deg C, and measured 503.73+-22.57 micro m in mouth height. The average number of rotifer in the digestive tract at the start of feeding was 0.57 individual/larva. A starvation experiment was carried out using a 15-liter glass aquarium (water volume 10 liters) with three replications. Five hundred newly hatched larvae of Siamese gourami were kept without feeding. Larvae started to die at 72 hr and totally died within 156 hr after hatching at water temperature ranging between 27.0 and 30.5 deg C.