The planktonic shrimp Acetes intermedius is an ecologically and commercially important species. Since it was described by Omori(1975) as a new species, there have been relative few studies focused on the reproduction of this species. The aim of this study is to examine the spawning, egg hatching, larval development of A. intermedius and the related environmental factors.
The newly released eggs of Acetes intermedius were round, 200 um in diameter in average, transparent, demersal and were usually green in color. The cleavage pattern of developing egg is holoblastic. Larval stages could be divided into four stages: nauplius, protozea, zoea and postlarva. Nauplius, protozoea and zoea can be further divided into 4, 3 and 2 substages, respectively. At water temperature 30 ¢J and salinity 25 psu, hatching of nauplius was around 10-11 h after spawning while protozoea, zoea and postlarva occurred around 29h, 5-6 and 7 days after spawning, respectively.
Newly released eggs were introduced directly into different temperature-salinity combinations. The results revealed that eggs failed to hatch at 15¢J at all salinities tested and at salinities 0 to 10 psu at all temperatures examined. Hatching success started to decrease at salinity 15 psu at 30¢J and at 20 psu at both 25¢J and 20¢J. When salinity was not lower than 25 psu, the hatching success reaches nearly 90 % in average and is generally similar among temperatures tested. Hatching started at about 10, 14 and 28h after spawning at temperatures 30, 25, 20¢J, respectively. At salinity 25 psu, hatching time was the shortest at both 25 and 30¢J, whereas it was similar among salinities at 20¢J.
Eggs and nauplii I hatched at 30 ¢J, 30 psu were incubated in the different temperature-salinity combinations. It took eggs incubated at salinities ranging from 20 to 35 psu about 28, 45 h and 5 days to develop into protozoea I at 30, 25 and 20 ¢J, respectively. Nauplii usually started to metamorphose earlier at 25 and 30 psu than at 35 and 20 psu at 25 and 30¢J while no significant trend in metamorphosis time was found among different salinities at 20¢J. Nearly 90% of nauplii metamorphosed into protozoea I at 25 and 30¢J while the metamorphosis rate of nauplii was greatly reduced at 20¢J. The metamorphosis rate was usually higher around 20-25 psu and lower at 15 and 35 psu in all temperatures examined.
While spawning, the gravid females swam near the water surface and were rapidly beating pleopods. The eggs were directly released into water. Spawning usually took place at night but the timing is generally peaked around midnight. The gravid females spawned in the early spring before midnight while they spawned after midnight in summer. The spawning timing is delayed at low temperature (24¢J) while it is not affected by high temperature (30¢J). The salinity did not show any effects on spawning but the hatching success of eggs released at 15 and 35 psu was significantly lower than those at 20-30 psu. The gravid females were tended to be endogenous timed to spawn in the night since spawning was not affected by absence of presence of light.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0731100-161915 |
| Date | 31 July 2000 |
| Creators | Chen, Yung-Hui |
| Contributors | L. S. Fong, I-Ming Chen |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0731100-161915 |
| Rights | not_available, Copyright information available at source archive |
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