The monthly mean weight and total length of T. alboplumbeus (Richardson) in the culture (March to September 2002) are shown in Table 1. The error bars in Figures 4 and 5 were the standard deviation of the weight and length measurements.

　

The growth rates of T. alboplumbeus (Richardson) from March to September 2002 were 3.1 g/month and 1.7 cm/month (calculated from the slopes of the best fit lines in Figures 4 and 5 respectively). The mortality rate within the same period was observed to be 52 percent.

　

　

　

　

According to the growth rates of T. alboplumbeus (Richardson) in the summer months (April to September in Hong Kong) obtained in this study, the projected weight and length of the fish at the end of 2003 (about 22 months of rearing in fish cage) would be 55.8 g and 30.6 cm respectively (Fig.6). Typical grown-up and mature T. alboplumbeus (Richardson) Specimens (Fig.7) were, however, found to be within the ranges of 35 - 81 g and 15 - 20 cm (Yu and Yu, 2002). Therefore, the projected weight of the cultured specimens after 22 months of rearing in fish cage would be within the typical range but the projected length would not be, which might be due to the slowing down of the growth rate in length when the fish grow up and increase in body weight.

　

The mortality rate (52%) was found to be more than half of the total number of fish in the first seven months of culture, which might be due to the following contributing factors: (1) the feed was not suitable for the juveniles in terms of nutrition and palatability, (2) cannibalism happened among the fish because of large size heterogeneity or overcrowding, and (3) epidemic diseases were frequent among the fish in a confined fish cage. It should be pointed out that the fairly high growth rates in weight and length observed in this period might partly due to the remaining stronger survivors left, which might not truly reflect the actual growth rates. The use of a suitable artificial feed for fish juveniles to start with and the monitoring of similar size of fish being reared in the same cage will certainly improve the survival rate in future experiments.

　

Jiang et al. (2000) reported that, among the 22 species of puffer fish belonging to the genus Takifugu found in Chinese waters, there were only about 4 species suitable for cultivation, and all of which took more than two years to grow up and mature. Moreover they also required special facilities for overwintering because they will die when the culture water fell below about 7℃ (Sun et al., 2000). As Hong Kong has a sub-tropical climate, the culture of T. alboplumbeus (Richardson) does not require any overwintering facility and it can mature and grow up within 2 years, which is shorter than the culture time of the northern species. However, T. alboplumbeus (Richardson) is a relatively small species and it seldom reaches more than 200 g each, whilst those northern species can normally reach over 500 g each.

　

In view of fully utilizing the local marine resources, the mariculture of puffer fish in Hong Kong is certainly feasible and will create more working opportunities among the fishing communities. The present study has preliminarily showed that T. alboplumbeus (Richardson) is another marine puffer fish species feasible for culture in fish cages. However, further studies are required to improve the survival rate of the fish and the introduction of artificial feed will improve the fish growth rate (Liang et al., 2001) and slow down the ageing of the culture zones (Pawer et al., 2002). Moreover, the exploration of natural or artificial spawning of puffer fish for the production of a steady supply of larval fish of high quality and homogenous size for culture (Dinis et al., 1999; Jiang et al., 2000), which would be much better than collecting the fish juveniles from the wild. This would be an important criterion for a cultured species to be successfully cultivated in future.

　

There were reports from China (Jiang et al., 2000), Japan (Saito et al., 1984) and Taiwan (Lin et al., 1998; Hwang et al., 2000) that cultured puffer fish were non-toxic or in reduced toxicity when compared with the same species caught from the wild. However there is still no information available about the toxicities of the cultured puffer fish in Hong Kong, which will require further studies to be undertaken by the authors when the fish grow up and mature. Therefore, the grown-up cultured puffer fish could be exported overseas either as live fish or processed as frozen fish fillets. The toxic viscera can be used for the extraction of the valuable neurotoxin, tetrodotoxin (TTX), which, to the best of our knowledge, is still the current practicing method to produce TTX for sale in the world market. At present, large-scale production of TTX from TTX-producing bacteria in vitro is still not well developed and successful.