Department of Applied Biology & Chemical Technology

The Hong Kong Polytechnic University

HONG KONG

95983046r@polyu.edu.hk

　

　

During the period 1996-2002, nine species of puffer fishes were identified by us in Hong Kong waters. Although a total of twenty-six marine fish culture zones have been established in Hong Kong since the 1980s, puffer fishes are not among the cultured species as they are toxic and so are banned from marketing and consumption by the Hong Kong Government. Nevertheless, in some local restaurants, the serving of puffer fish is allowed if the fish are shown to be imported directly from Japan with the required health certificates.

　

Among the nine local species of puffer fish, most of which were reported to be toxic, we confirmed three species to be toxic and only one was non-toxic with the standard mouse bioassay. Moreover, the annual toxicological profiles of two toxic species revealed that the toxicity of their flesh was less than 10 mouse units per gram throughout the whole year. With proper processing, screening and storage methods, the flesh of most puffer fish is able to meet the safety standards of Japan and China for human consumption.

　

To fully utilize the local marine resources in Hong Kong, puffer fishes should be potential candidates for aquaculture in the near future. Apart from the flesh being for human consumption, the toxic viscera of puffer fish (mainly ovaries and liver) can be explored to produce the valuable tetrodotoxin (a neurotoxin mainly found in puffer fishes), which is a potential anesthetic and neuropathic pain drug, a proposed formulation to treat heroin addiction and a known cancer cell suppressor.

　

Keywords: Puffer fish; Marine fish culture zones of Hong Kong; Tetrodotoxin

　

　

The Hong Kong fishing industry used to be very important and support the livelihood of the local fishing communities before the 1960s. By then, the local marine fish catch was sufficient to meet the domestic demand and the surplus was usually for producing some side-business, such as sun-dried fish, salted fish, fish sauce, shrimp paste, etc. However, due to a number of factors. (1) the deterioration of seawater quality caused by pollution, rapid population growth and unmonitored industrial and domestic sewage, (2) a drastic decrease in coastal fish breeding grounds caused by large scale land development, (3) over-exploitation, etc., the fisheries resources in Hong Kong waters and the South China Sea as a whole has dramatically decreased over the past several decades, especially for the high value fishes (Environmental Resources Management, 1998).

　

The introduction of the marine fish culture zones along the Hong Kong costal waters by the Hong Kong Agriculture and Fisheries Department (which becomes the Agriculture, Fisheries and Conservation Department in 2000) in the 1980s helped to alleviate the shortage problem of fisheries supply for a short while. The common cultured fishes were highly esteemed species such as the groupers, sea breams, snappers, etc. Unfortunately, the mariculture industry (mariculture) died down rapidly as a result of water pollution, aging of the culture zones, red-tides, epidemic fish diseases, etc.

　

To date, the local fisheries supply, live, chilled or frozen, is mainly imported from mainland China, some Southeast Asian countries and some other western countries. Hong Kong people used to consume a lot of live marine fish, apart from being very delicious but also very nutritious, which is one of the main sources of the human essential proteins.

　

With the recent decline in the local fisheries resources, puffer fishes can still be easily caught along the coastal waters. A total of nine species (belonging to five different genera) has been identified and reported by us (Yu and Yu, 2002a, 2002b) which coincided with the number of species in the reports of Chan (1968), but the species were different. However puffer fish are not among the cultured species as they are toxic and are banned from marketing and consumption by the Hong Kong Government except in some restaurants where puffer fishes were imported directly from Japan and which were accompanied with health certificates showing they are safe for human consumption.

　

The mariculture of puffer fish has long been practiced in Japan since the 1960s (Pawar et al., 2002) as puffer fish have long been an expensive delicacy among the Japanese, especially the species Takifugu rubripes (Temminck & Schlegel) (Fig.1) served in the restaurants. Moreover, processed frozen puffer fish fillets are commonly available on sale in the Japanese fish markets for household consumption (Fig.2). Puffer fishes are also cultured in mainland China, Taiwan and Korea, for both local consumption and exportation. The two marine species, T. rubripes (Temminck & Schlegel) and T. chinensis (Abe), cultured in northern China are solely for exporting to Japan and the two anadromous species, T. ocellatus (Linnaeus) and T. obscurus (Abe), which migrated to the Yangtze estuary in eastern China during their spawning seasons in March to April every year, are mainly for local consumption (Jiang et al., 2000).

　

There was hardly any attempt which had ever been made to investigate the culture and growth rates of puffer fish in captivity in Hong Kong where they have never been considered as food fish, except for the non-toxic species (Lagocephalus wheeleri, Abe, Tabeta and Kitahama) among the minor fishing community (Yu and Yu, 1997, 1998). A feasibility study on the mariculture of puffer fish in Hong Kong is, therefore, being conducted with a view to explore the possibility of using local puffer fish resources as new cultured candidates. So some common local puffer fish juveniles were collected along the coastal waters and reared in cages in order to observe their growth rates, feeding habit and mortality during culture.

　

With proper processing, screening and storage methods, the toxicity of the flesh of most puffer fishes is less than ten mouse units per gram in mouse bioassay, which is actually safe for human consumption (Ministry of Health and Welfare, Japan, 1991; Yu and Yu, 2001, 2002a). Besides the skin of puffer fish is a potential source of collagen which is an essential human protein (Nagai et al., 2002), the toxic viscera of puffer fish (mainly ovaries and liver) can be explored to produce the valuable tetrodotoxin (a non-protein neurotoxin mainly found in puffer fishes), which is also a potential anesthetic (Kohane et al., 1998), a promising neuropathic pain drug (Lyu et al., 2000), a proposed formulation to treat heroin addiction (Sellers et al., 2002) and a known cancer cell suppressor (Fraser et al., 1999).

　

　

　

　

Puffer fish juveniles of T. alboplumbeus (Richardson), measuring from 4 to 6 cm in total length (Fig.3), were found swimming and feeding in large numbers along the seashore from March every year immediately after their spawning season from December to February (Yu and Yu, 2002). This species is one of the most commonly found local puffer fish (common name is known as Hong Kong Puffer fish) and the fish juveniles were easily collected with fishing net in coastal waters.

　

A total of 100 healthy specimens of T. alboplumbeus (Richardson) were collected along the shores in March 2002. They were weighed and measured individually and the healthy juveniles were reared in a net cage suspended in floating wooden fish raft at one of the marine culture zones in Hong Kong.

　

With reference to the mariculture practices and techniques for fish floating cage farming recommended by the Hong Kong Agricultural, Fisheries and Conservation Department (Agriculture, Fisheries and Conservation Department. 2001), the size of the fish cages used in this experiment were about 2x2x2 m and the mesh size was adjusted as the fish grew up. The cage was covered with a net to prevent the fish from being caught or eaten by some flying birds.

　

New and clean cages would replace fouled cages regularly to maintain water current passing freely through the cages. The stocking density of the fish was kept at an optimal level (between 10 - 20 tails per cubic meter from juveniles to adults) to prevent overcrowding which would cause biting and coeval (sibling) cannibalism among themselves (Baras et al., 1999). The fish were fed daily with ground trash fish once in the morning until satiety. About 10% of the fish were weighed and measured (total length) every month to assess the growth rate. Dead and diseased fish were removed immediately from the cage everyday.

　

There were reports emphasizing that puffer fishes were instinctive biters which caused large-scale damages to fish cages and fishing gears (Naik, 1998). In order to prevent damage to the fish cage (hence escape and loss of fish), which was commonly made of polyethylene, by the sharp teeth and strong jaws of the fish when they grew up, the cage was replaced with metal cage when the fish approached about 50 g each.