Songklanakarin Journal of Science and Technology (SJST) (Feb 2005)
Some aspects in early life stage of climbing perch, Anabas testudineus larvae
Abstract
The sexual maturity of female climbing perch, Anabas testudineus was studied by determining fecundity and gonadosomatic index (GSI). It was found that the size at sexual maturity of female climbing perch was 15.20±1.24 cm (mean±SD) in total length and 61.10±17.32 g in body weight. The eggs were floating and rounded. The fertilized eggs had a diameter of 830±39 μm. The fecundity was 24,120.5±3,328.24 ova/ fish and gonadosomatic index (GSI) was 10.4±2.5%. Newly hatched larvae of climbing perch 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 2:1. The fertilization rate, hatching out and hatching rate experiments were carried out using a 15-liter glass aquarium (water volume 10 liters) containing 7,000-9,000 eggs. It was found that the eggs were floating and rounded. The fertilized eggs had a diameter of 830±39 μm. The average fertilization rate was 92.67%, hatching out was 20 hr 30 min and average hatching rate was 87.44% at a water temperature of 27.0-30.5ºC. Sampling of the newly-hatched larvae was done at 2-hour intervals, when 20 of them were randomly taken and preserved in 10% buffered formalin for later deter-mination of yolk absorption time. Observation using a microscope revealed that newly hatched larvae were 2.02±0.20 mm in total length and had yolk sacs of 111.33±46.19 mm3 in volume. The yolk sacs were completely absorbed within 92 hr after hatching at a water temperature of 27.0-30.5ºC. 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 28 hr after hatching (2.95±0.59 mm TL), with the mouths measuring 328.42±32.23 mm in height. The feeding experiments were carried out using a 15-liter glass aquarium (water volume 10 liters) containing 1,000 larvae aged 1 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% buffered formalin, and then dissected to determine the presence of rotifer in the digestive tract. The digestive tracts were fixed at 32 hr of hatching at water temperatures of 27.0-30.5ºC, and measured477.63±47.80 mm in mouth height. The average number of rotifer in the digestive tract at the start of feeding was 1.50 individual/larva. A starvation experiment was carried out using a 15-liter glass aquarium (water volume 10 liters) with three replications. Two hundred newly hatched larvae were kept without feeding. Larvae started to die at 216 hr and totally died within 348 hr after hatching at water temperature ranging between 27.0 and 30.5ºC. The feeding scheme experiments were done in a 15-liter glass aquarium (water volume 10 liters) containing 500 of two-day old larvae (stage at first feeding). It was found that larval climbing perch aged 3- 10 days (average total length 3.02-4.97 mm) consumed rotifer. The larvae of age 8-15 days (average total length 3.94-12.60 mm) consumed Moina. The larvae of age 8-10 days (average total length 3.94-4.97 mm)consumed both rotifer and Moina. The larvae of age 11-day (average total length 5.51 mm) consumed only Moina. The larvae of age 14-15 days (average total length 7.34-12.60 mm) consumed both Moina and artificial feed. Larvae aged more than 16 days consumed only artificial feed. Determining the daily food uptake by the larvae and juveniles was done in a 15-liter glass aquarium (water volume 10 liters) containing 100 larvae. The larvae consumed the living food organism i.e. rotifer or Moina depending on larval stage, with density of rotifer 100 individual/ml or with density of Moina 10 individual/ml. The amount of food intake was calculated based on changes of food density in the aquariumwith and without fish larvae at 2-hour intervals. It was found that the larvae of age 3-6 days (average total length 3.02-3.71 mm) consumed only rotifer. The average uptake of rotifer in digestive tract per day of larvae age 3 and 6 days old were 9 and 16 individual/larva, respectively. The 9-days old larvae (average total length 4.43 mm) consumed both rotifer and Moina, the average uptake of rotifer in digestive tract in a day was 19 individual/larva and that of Moina was 10 individual/larva. The larvae of age 12-15 days (average total length 6.11-12.60 mm) consumed only Moina. The average uptake of Moina in digestive tract per day of larvae age 12 and 15 days old were 98 and 113 individual/larva, respectively.
