Some aspects in early life stages of larval red-tail catfish, Mystus wyckioides

1999

Thumronk Amornsakun

Larval red-tail catfish were produced by induced spawning using hormone injection (Suprefact and Motilium). Sampling of the newly-hatched larvae was done at 2-hour intervals, when 20 of them were randomly taken and preserved in 5 percent buffered formalin solution for later analysis to determine the time of final yolk absorption. Observation using a microscope revealed that newly hatched larvae were 4.59+-0.28 mm in total length and had large yolk sacs of 1443.17+-475.55 micro cubic m volume. The yolk sacs were completely absorbed within 104 hr after hatching at a water temperature of 28-30.5 deg C. Up until full mouth development (start of feeding), 2 hourly samplings of twenty newly hatched larvae were taken from a fiber-glass hatching tank for observation of the size of mouth opening. All the larvae had open mouths about 26 hr after hatching (7.14+-0.70 mm TL), with the mouths measuring 324.86+-124.40 micro m in mouth height. The start of feeding experiments were carried out using a 15 liter aquarium (water volume 10 liters containing 1000 larvae aged 1.5 days post-hatching (just the mouth opened). They were fed with Moina at a density of 5-10 ind/ml. Twenty larvae were collected at random from the aquarium at 2-hourly intervals, preserved in 5 percent buffered formalin solution, and then dissected to determine the presence of Moina in the digestive tract. Some digestive tracts developed fully within 64 hr of hatching at water temperature of 28-30.5 deg C, and measured 534.67+-102.75 micro m in mouth height, contained numbers of Moina of width 242+-24.65 micro m. The average number of Moina in the digestive tract at the start of feeding was 1.3 individual/larva.

[Warasan Songkhlanakharin]

2004/TH/TH2004_0.rdf