American eel, Anguilla rostrata, growth in fresh and salt water: implications for conservation and aquaculture

Growth of American eels, Anguilla rostrata (Lesueur), sampled in saltwater bays and adjacent fresh- water ponds in the southern Gulf of St. Lawrence, Canada, was estimated by otolith annulus back-calculation, and related to salinity of growth habitat as determined using otolith strontium:calcium ratios. Eels resident in salt water grew on average in length 2.2 times faster than freshwater residents and increased in weight 5.3 times faster than freshwater residents. Previous findings of superior American eel growth rate in brackish water are thus extended to full-strength salt water. Freshwater residents took an estimated 2.4 times longer than saltwater residents to reach the silver eel stage. The extended time to maturation of eels reared in fresh water increases their vulnerability to fisheries and to bio-accumulation of contaminants. Freshwater eel populations should be managed more conservatively than those in saline waters. The increase in eel growth with salinity suggests that rearing in brackish or salt water could improve growth rates in eel aquaculture.