The effects of saline environments on survival and growth of eggs and larvae of Chirostoma estor estor Jordan 1880 (Pisces: Atherinidae)

Pescado blanco, Chirostoma estor estor, is a species unique to certain Mexican altiplano lakes and is under severe environmental and fishing pressure, to the point of becoming endangered. C.estor estor is now part of a programme designed to develop aquaculture technology for the species which will preserve biodiversity, enable restocking and provide a basis for semi-intensive aquaculture. Although now fully adapted to freshwater, members of the genus Chirostoma are derived from estuarine or coastal ancestors many of which are euryhaline. This paper describes investigations of salinity tolerance in C. estor estor, designed to improve hatchery strategies and hence survival and growth. Eyed egg development was high in freshwater, maximal at about 10 ppt, and then significantly reduced at higher salinities. Saprolegnia infection rate was very high in freshwater, but reduced markedly at 5 ppt and was abolished at higher salinities. Hatching success was greatly increased by rearing eggs in moderate salinities, but allowing hatching to take place in freshwater. This may be related to inhibition of activity of chorionase or mobility of the larvae at higher salinities. Instantaneous transfer of larvae to a range of salinities resulted in very high mortalities above 10 ppt. Following 48-h acclimation to salinities up to 15 ppt, maximum survival rate over 30 days was obtained at 10 ppt. In terms of survival, optimum practice would be for egg development to occur at 10 ppt, hatching to occur at 5 ppt and subsequent development to take place at 10 ppt. Growth in dry weight over 30 days was greater at 10 ppt and 15 ppt and was significantly greater than that recorded at 0 ppt and 5 ppt. Overall, the results reveal the euryhaline capabilities of the species, and this can clearly be related to an estuarine or coastal ancestry, from which the species group radiated relatively recently. The implications and advantages of using saline environments for optimal husbandry of eggs and early larvae are discussed.