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THESIS APPROVAL

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study. However, it might be assumed that new offspring of L. hoffmeisteri may be<br />

produced due to the completion of their life cycle reaching. Ongoing studies<br />

investigating the life cycle and production of L. hoffmeisteri in Chao Phraya estuary is<br />

warranted.<br />

Number of individual and weight of the worms were more increased in<br />

E-WH than in E-WL since more level of food was input to the sediment. These<br />

results suggest that the quantity of food addition strongly influenced growth and<br />

reproduction of L. hoffmeisteri. Because this oligochaete species can thrive on soft<br />

sediments rich in organic matter, dense colony of L. hoffmeisteri could feed on<br />

available organic material assimilated in the sediment (Collado and Schmelz, 2001).<br />

Martin et al. (1999) stated that the quantity of food is a factor affecting density and<br />

distribution of aquatic oligochaetes. It was also supported by the work of Leppanen<br />

and Kukkonen (1998a) who found that the oligochaete Lumbriculus variegatus<br />

decreased reproduction in sandy sediment with low organic carbon content. Similar<br />

response in reproduction was observed also by Hickey and Martin (1995) between<br />

sandy and muddy New Zealand sediments, and Phipps et al. (1993) between<br />

sediments with low (1-2%) and high (8-10%) organic carbon content.<br />

However, abundant organic material was not immediately available for<br />

the growth and reproduction of L. hoffmeisteri in the first stage of this experiment<br />

although the same amount of food was added in the sediments. This suggestion was<br />

arisen from the decrease of number of individual and weight of the worms in both<br />

E-WL and E-WH around 14 d, followed by the appearance of specific growth in<br />

E-WH during 35 d from the start of the experiment. On the other hand, it could be<br />

said that weak animals may be died, while strong worms may lose weight and attend<br />

to reach sexual maturity and fecundity in the early stage (d 14). Subsequently,<br />

individual worm grew up and reproduced new offspring in the later period (d 35) of<br />

the experiment. These results agree with the data of White et al. (1987), in which the<br />

slowing of feeding of Stylodrilus heringianus was connected with reproductive<br />

behavior, and Leppanen and Kukkonen (1997), in which the ingestion of<br />

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