Effects of a novel weakened whole‐cell form of Haematococcus pluvialis on flesh pigmentation of rainbow trout ( Oncorhynchus mykiss ) when compared to synthetic astaxanthin

Abstract

Fillet colour is an important quality indicator for consumers. To achieve flesh colouration in farmed salmonids, synthetic astaxanthin (Ax) pigment is added to the feed. Cost, safety and consumer preference are increasing research efforts for non-synthetic Ax alternatives. Haematococcus pluvialis (Hp) is an efficient producer of Ax but has not been effective in pigmenting salmonid flesh due to its rigid cell wall structure. A novel form of Hp has been cultivated to possess a weakened cell wall, which may increase Ax bioavailability. To assess pigmenting ability, Ax retention, tissue content and fillet colouration were measured in rainbow trout (Onchorhynchus mykiss) fed diets containing this pre-commercial Hp product. Sixty rainbow trout (992 g ± 177.24 g) were PIT (passive integrated transponder)-tagged, distributed among six tanks and fed one of three experimental diets: No Ax (N-Ax), synthetic Ax (S-Ax; 80 mg/kg Ax) or Ax from Hp whole cells (Hp-Ax; 60 mg/kg Ax). After 10 weeks, tissue Ax content and flesh colour were assessed. No significant (p > 0.05) differences were evident in either growth metrics, fillet Ax content, retention or colouration were observed between S-Ax and Hp-Ax treatments. Ax retention was 15.4 ± 0.23%, respectively, for fish fed the Hp diet. SalmoFan™ colour readings of S-Ax and Hp-Ax fillets ranged from 28 to 34 and were significantly higher than N-Ax fillets (p < 0.001). This novel whole-cell Haematococcus pluvialis was equally efficient at pigmenting the flesh of rainbow trout compared with synthetic Ax.