Effects of day length and cleaning regimen on the growth of yearling parr Atlantic salmon

Yearling Atlantic salmon (Salmo salar) were reared with 8 or 16 h of light each day in laboratory tanks that were cleaned daily or weekly, and growth was measured weekly for 10 weeks. Growth was greatest for fish on the 16‐h light and weekly cleaning routine. Reduced frequency of tank cleaning (weekly) significantly enhanced growth but accounted for only 8.5% of the partitioned variance, compared with 78.9% for increases in day length alone. Results of this study suggest that the increased growth observed at longer day lengths was primarily due to the stimulatory effects of increased amounts of light.