Cephalopods become one of the most important commercial marine resources worldwide. The knowledge of the basic biology and population dynamics of these resources is the way to ensure the resource to be utilized properly. In Taiwan, cephalopods are traditionally used and prized as foods with high market price. Sepioteuthis lessoniana is an important fishery species. Its distribution is concentrated around the northeastern and the southern coasts of Taiwan, and the Peng-Hu Island. Although there are some investigations on the statolith of the adults, studies on early stages are scarce. In this study, we use the known-age statoliths incubated in the different conditions to relate with those factors, i.e., temperature, salinity, and photoperiod, which influenced the ring formations during the embryonic and larval stages.
From April to September, several clusters of bamboos, 3 ~ 4 m long, 1 ~ 2 m wide, were set on the sea bed at a depth of 16 to 20 m to attract their spawning, and the egg-strings were then transported to the laboratory. When the development of the embryo reached stage 24, iris of eyes being prominent as a colour circle and statolith being formed, they were transferred into different rearing conditions, i.e., 20, 25, 30, 35 o/oo and 15, 20, 25, 30 oC. The durations from stage 24 to hatching were different among all different rearing conditions. The statoliths were extracted and mounted in Crystal Bond thermoplastic cement for reading their growth rings. In the normal condition (25 oC and 35 o/oo), the duration from stage 24 to hatching is 9 ~ 16 days. Although the rings can be counted in each specimen, the numbers do not match between the embryonic rings and the developmental duration.
Changes on the shape of the statolith were observed among different incubated conditions. The shape of the statolith at hatching had obvious differences among different embryonic developmental conditions. The statolith developed in the colder environment had smaller dorsal dome, thinner and shorter rostrum than that developed in the warmer condition. Using the shape of this embryonic ring was to be applied to measure the variation of the shape of the statolith. This is a useful tool to know the temperature factor during embryonic development by comparing with the shape of the hatchling¡¦s statolith.
After hatching, squid hatchlings were separated to incubate in two different photoperiod regimes, 12 hr: 12 hr and 24 hr constant light conditions. Squid larvae were maintained as long as possible. Although the trend which older squids have more increments on the statolith than younger squids is consistent, the slope between the increments and survival days is less than one. The time required to form one ring on the statolith is needed for more than one day. Bell-shaped distributions can be found in several analyses in this study, especially with large sample size in 25 oC at 35 o/oo. If the sample size was small, the bell-shaped distribution would be obscure. This may result in oversimplification in interpretating the result. Sometimes this kind of problem could be inevitable because collecting large enough sample size was difficult or impossible. In any validation exercise, it would be difficult to obtain data for the whole life cycle. This study indicated that the hypothesis of daily-increment for the whole life history required further verification with larger sample size and wider size ranges of the tropical squids in future.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0729103-094337 |
| Date | 29 July 2003 |
| Creators | Chung, Wen-Sung |
| Contributors | Wann-Nian Tzeng, Hui-Mei Su, Chien-Chung Hsu, Chung-Cheng Lu |
| 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-0729103-094337 |
| Rights | unrestricted, Copyright information available at source archive |
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