Aspects of natural and artificial hybridization between Brown Trout and Atlantic Salmon in Newfoundland

McGowan, Colin (1992) Aspects of natural and artificial hybridization between Brown Trout and Atlantic Salmon in Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Two projects were undertaken to obtain information at the molecular, organismal and ecological levels of organization concerning the causes and dynamics of natural hybridization between brown trout (Salmo truttta L.) and Atlantic salmon (Salino salar L.) in Newfoundland. -- (1) Protein electrophoresis and mitochondrial DNA analysis were used to detect the frequency and direction of natural hybridization between these species in nine Newfoundland rivers. In total, 37 hybrids were discovered in a sample of 792 juvenile fish for a regional frequency of 4.7%. Local frequencies ranged from 0 to 18.7% and were significantly heterogeneous. All of the hybrids sampled were produced from matings between female brown trout and male Atlantic salmon. -- (2) The relative viability of hybrids produced using anadromous brown trout, Atlantic salmon grilse and sexually mature Atlantic salmon parr from a Newfoundland river was investigated. The sperm of sexually mature salmon parr performed equally well compared to anadromous salmon sperm when fertilizing both salmon and trout eggs. Hatching success was high in all crosses and controls. By first feeding, hybrids produced using brown trout eggs had suffered higher mortality and were smaller in size than the reciprocal hybrid and both parental controls. Hybrids produced using salmon eggs exhibited high viability and by first feeding were greater in size than both parental controls. A comparison of hatching time and length of hatching period suggests a paternal influence in embryo development. -- Possible reasons for the breakdown of prereproductive isolating mechanisms between Newfoundland brown trout and Atlantic salmon are considered in light of the contrasting results obtained from the two investigations. Reproductive characteristics of the populations involved appear to have a major influence on the dynamics of hybridization between these species in Newfoundland. It is proposed that an abundance of sexually mature Atlantic salmon parr in Newfoundland streams is responsible for both the frequency and direction of hybridization observed in this study. Possible reasons for the differences in viability of reciprocal hybrids and the significance of results with respect to the aquaculture industry are also discussed.

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