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level of the shellfish toxicity is still low, but it increases to a higher level and reaches a maximal level after most of the dinoflagellates disappear from the environment. There is always about a 1 week time lag between the peaks of these parameters (Ogata et al. 1982, Sekiguchi et al. 1989). This phenomenon is difficult to explain if the toxins in the dinoflagellates transfer to the shellfish via the food chain. However, it is hard to evaluate the balance of the toxin amount between dinoflagellates and shellfish in a field survey in which samples of shellfish and plankton are collected periodically at a station set in the field, even though the frequency of the sampling is increased. Thus, the nature of the balance of the toxins be tween shellfish and dinoflagellates has not been clarified by data from field surveys. Recently, we examined this problem by feeding dinoflagel lates to shellfish. As handling of the shellfish during the experiments was found to affect much the feeding behavior of the shellfish (Sekiguchi et al. 2001a), a single specimen of shellfish was reared in a single tank, and the known amount of the cultured cells of dinoflagellate was fed to the shellfish specimen (Sekiguchi et al. 2001b). These experiments showed that shellfish accumulate toxins by ingesting the toxic dinoflagellate, and they release a part of the toxins to the environmental water even while ingesting the dinoflagellate. When the feeding stopped, the shellfish ex creted the toxins continuously. The profile of excreted toxins was similar to that accumulated in the shellfish, that is, shellfish release the toxin components non-selectively. Interestingly, the amount of toxins accumulated in the shellfish was not parallel to that of dinoflagellate cells fed to the shellfish (Fig. 8). At the earlier period of the experiment when shellfish were ingesting the cells, the amount of toxins accumulated in the shellfish was often more than that in the dinoflagellates fed to the shellfish. In the later period when the feeding was stopped, the sum of the toxins in the shellfish and rearing water had decreased to a level which was less than that introduced from the dinoflagellates cells, showing that some amount of toxins disappeared from the experimental system. However, this level recovered to the almost same level as that derived from the fed cells of the dinoflagellate, when they were further reared. These facts indicate that a part of the toxins was transformed to an unknown form which could not be detected by chemi cal analysis, such as HPLC. The unknown form of the toxins is gradually transformed to toxins again in the shellfish which can be detected by the chemical analysis. The unexpected high level of toxins accumulated in the shellfish, more than the fed amount of toxins, may show that an unknown form of toxins occurs also in the dinoflagellate fed to the shellfish. Thiol compounds of biological origin, such as GSH, are thought to be involved in the formation of the unknown form of toxins. Proteinous thiols such as that with a cystein residue may be involved in the formation of the
DOI link for level of the shellfish toxicity is still low, but it increases to a higher level and reaches a maximal level after most of the dinoflagellates disappear from the environment. There is always about a 1 week time lag between the peaks of these parameters (Ogata et al. 1982, Sekiguchi et al. 1989). This phenomenon is difficult to explain if the toxins in the dinoflagellates transfer to the shellfish via the food chain. However, it is hard to evaluate the balance of the toxin amount between dinoflagellates and shellfish in a field survey in which samples of shellfish and plankton are collected periodically at a station set in the field, even though the frequency of the sampling is increased. Thus, the nature of the balance of the toxins be tween shellfish and dinoflagellates has not been clarified by data from field surveys. Recently, we examined this problem by feeding dinoflagel lates to shellfish. As handling of the shellfish during the experiments was found to affect much the feeding behavior of the shellfish (Sekiguchi et al. 2001a), a single specimen of shellfish was reared in a single tank, and the known amount of the cultured cells of dinoflagellate was fed to the shellfish specimen (Sekiguchi et al. 2001b). These experiments showed that shellfish accumulate toxins by ingesting the toxic dinoflagellate, and they release a part of the toxins to the environmental water even while ingesting the dinoflagellate. When the feeding stopped, the shellfish ex creted the toxins continuously. The profile of excreted toxins was similar to that accumulated in the shellfish, that is, shellfish release the toxin components non-selectively. Interestingly, the amount of toxins accumulated in the shellfish was not parallel to that of dinoflagellate cells fed to the shellfish (Fig. 8). At the earlier period of the experiment when shellfish were ingesting the cells, the amount of toxins accumulated in the shellfish was often more than that in the dinoflagellates fed to the shellfish. In the later period when the feeding was stopped, the sum of the toxins in the shellfish and rearing water had decreased to a level which was less than that introduced from the dinoflagellates cells, showing that some amount of toxins disappeared from the experimental system. However, this level recovered to the almost same level as that derived from the fed cells of the dinoflagellate, when they were further reared. These facts indicate that a part of the toxins was transformed to an unknown form which could not be detected by chemi cal analysis, such as HPLC. The unknown form of the toxins is gradually transformed to toxins again in the shellfish which can be detected by the chemical analysis. The unexpected high level of toxins accumulated in the shellfish, more than the fed amount of toxins, may show that an unknown form of toxins occurs also in the dinoflagellate fed to the shellfish. Thiol compounds of biological origin, such as GSH, are thought to be involved in the formation of the unknown form of toxins. Proteinous thiols such as that with a cystein residue may be involved in the formation of the
level of the shellfish toxicity is still low, but it increases to a higher level and reaches a maximal level after most of the dinoflagellates disappear from the environment. There is always about a 1 week time lag between the peaks of these parameters (Ogata et al. 1982, Sekiguchi et al. 1989). This phenomenon is difficult to explain if the toxins in the dinoflagellates transfer to the shellfish via the food chain. However, it is hard to evaluate the balance of the toxin amount between dinoflagellates and shellfish in a field survey in which samples of shellfish and plankton are collected periodically at a station set in the field, even though the frequency of the sampling is increased. Thus, the nature of the balance of the toxins be tween shellfish and dinoflagellates has not been clarified by data from field surveys. Recently, we examined this problem by feeding dinoflagel lates to shellfish. As handling of the shellfish during the experiments was found to affect much the feeding behavior of the shellfish (Sekiguchi et al. 2001a), a single specimen of shellfish was reared in a single tank, and the known amount of the cultured cells of dinoflagellate was fed to the shellfish specimen (Sekiguchi et al. 2001b). These experiments showed that shellfish accumulate toxins by ingesting the toxic dinoflagellate, and they release a part of the toxins to the environmental water even while ingesting the dinoflagellate. When the feeding stopped, the shellfish ex creted the toxins continuously. The profile of excreted toxins was similar to that accumulated in the shellfish, that is, shellfish release the toxin components non-selectively. Interestingly, the amount of toxins accumulated in the shellfish was not parallel to that of dinoflagellate cells fed to the shellfish (Fig. 8). At the earlier period of the experiment when shellfish were ingesting the cells, the amount of toxins accumulated in the shellfish was often more than that in the dinoflagellates fed to the shellfish. In the later period when the feeding was stopped, the sum of the toxins in the shellfish and rearing water had decreased to a level which was less than that introduced from the dinoflagellates cells, showing that some amount of toxins disappeared from the experimental system. However, this level recovered to the almost same level as that derived from the fed cells of the dinoflagellate, when they were further reared. These facts indicate that a part of the toxins was transformed to an unknown form which could not be detected by chemi cal analysis, such as HPLC. The unknown form of the toxins is gradually transformed to toxins again in the shellfish which can be detected by the chemical analysis. The unexpected high level of toxins accumulated in the shellfish, more than the fed amount of toxins, may show that an unknown form of toxins occurs also in the dinoflagellate fed to the shellfish. Thiol compounds of biological origin, such as GSH, are thought to be involved in the formation of the unknown form of toxins. Proteinous thiols such as that with a cystein residue may be involved in the formation of the
ABSTRACT
Fig. 8. The change in amounts of PSP toxins accumulated in scallop specimens separately in individual tanks (Sekiguchi el al. 2001b). The integrated amounts of toxins released from a single specimen and those supplied to each specimen by feeding Alezandrium tamarense cells are also shown. * A scallop extract was lost by accident.
