Simple, effective protocols for cryopreserving milt of five Brazilian migratory characids (Brycon orbignyanus, Prochilodus lineatus, Piaractus mesopotamicus, Salminus maxillosus and Leporinus elongatus) and one Brazilian migratory catfish (Pseudoplatystoma corruscans) are described. Milt was frozen and stored in dry shippers immediately after collection, making the procedure practical for use in the field. A diluent of 5% glucose, 10% dimethyl sulphoxide and 10% egg yolk was effective for all of the characid species, and a diluent of 10% methanol and 15% powdered milk was effective for P. corruscans. Milt was thawed in an ambient temperature water bath (28–30° C). Activation of thawed milt was effective with either saline (0·9 or 0·45% NaCl) or bicarbonate (1% NaHCO3). Fertilization rates with frozen milt varied between 49 and 300% of the control. Application of the technology for increasing genetic diversity in hatchery programmes for enhancement, mitigation or conservation breeding is discussed, as is its application in aquaculture. Inappropriate use of the technology can threaten wild biodiversity and appropriate legislation and education may be required for its responsible use.

To determine the functional variability of the gustatory system in salmonids, we examined electrical responses of the palatine nerve to amino acids in nine strains of rainbow trout (Oncorhynchus mykiss), four additional Oncorhynchus species, and two Salvelinus species. All species exhibited extreme sensitivity to L-proline. Besides the Pro receptors (interacting with L-proline, hydroxy-L-proline, and L-alanine), Phe (L-phenylalanine, L-leucine), AGP (L-α-amino-β-quanidinopropionic acid, betaine), and Arg receptors (L-arginine) were involved in amino acid detection. On the basis of the functional receptor types, the rainbow trout strains fell into two groups: (1) Kamloops, Manx, Mount Lassen, Sunndalsøra, Tagwerker, and Victoria and (2) Nisqually, Nikko, and steelhead. The former group originates primarily from inland waters, whereas the latter originates from coastal waters. Response patterns of other salmonid species were similar to those of group 2 rainbow trout. Response patterns did not change as a result of environmental conditions. We thus conclude that the functional variability of the gustatory system is not attributable to local environmental factors but rather may be genetic in origin. Similar variability may exist in responses to other chemicals, including toxicants, and we conclude that in studies employing salmonids it is important to identify the stock of fish in addition to the species.

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