THE EFFECT OF STARVATION ON FEEDING,GROWTH AND MORPHOLOGICAL DEVELOPMENT OF THE LARVAE OF MOSQUITO FISH

Mosquito fish Gambusia affinis is a small, ovoviviparous topminnow, native to the North America which had been an invasive species widely in the world.The larvae of this species were reared at about (28.5±1.2)℃in laboratory to examine the feeding ability change, growth and morphological development under starvation condition to investigate their early recruitment potential fluctuation affected by starvation factor.All larvae were divided into 3 groups :unfed, feeding and mortality observation group, each group were reared in three 2.5L glass tanks.Every day 5 larvae were taken from the culture tanks of unfed or feeding group to measure the morphological indexes in microscope respectively,while 10 larvae were taken to examine feeding ratio and intensity.The dead larvae of mortality observation group were recorded and removed every day. The results showed that the new born larvae developed perfectly, swam and preyed freely after 2 hours when the swim bladder was filled with gas,and used the yolk-sac to provide energy about 6 hours.Their mixed-nutrient stage lasted only 4 hours. During the experiment, the feeding ratio of feeding larvae was 100%while unfed larvae had feeding ratio at 100%when re-fedfrom 0d to 3d following by decreasing rate.On the 5thd, feeding ratio of unfed larvae was remarkable lower than those of feeding larvae.On the 6thd, unfed larvae feeding ratio was 0.Feeding ratio of unfed larvae had negative relationship with starvation time.The new born larvae feeding intensity on 1—2 stage mosquito larvae was (2.9 ±1.4)ind/ind·h, which increasing rapidly, and each 6-d-born fish can capture more than 11 mosquito larvae.After re-feeding, unfed larvae feeding intensity increased with their age during 0—4d, but was very remarkable lower than those of feeding fish at the same age,and dropped on the 5thd.There were no remarkable relationship between initial feeding ratio and initial feeding intensity of unfed larvae.The-point-of-no-return (PNR) was 5.5 day of unfed larvae.The death rate of unfed larvae was lest than 10%on 0—3d,(64.4 ±18.1)%on 4d and 100%on 6d while feeding larvae was no more than 5%.At the 6th day after birth, the venter fins of feeding larvae developed and different part of the body had different growth rate.The body depth (BD)and weight (W)of unfed larvae performed remarkable negative growth rate.Standard body length (SL)/Body depth (BD)ratio was higher than 5 in unfed larvae while lower than 4.5 in feeding larvae, which can be applied to distinguish the starvation and healthy larvae in field research.The relationship between larvae starvation tolerance and competitive ability and their invasion were also discussed in this paper.