Gonad enhancement of Evechinus chloroticus (Val.) in Otago Harbour, New Zealand, using artificial and macro-algae diets

Abstract

The endemic New Zealand echinoid, Evechinus chloroticus (Valenciennes), was collected bi-monthly between May 1999 and June 2000 from Elizabeth Island, Doubtful Sound, and held in shallow water sea cages in Otago Harbour, Dunedin, New Zealand. Three experiments (Sept-Nov 1999, Dec 1999-Feb 2000, Mar-May 2000) tested a range of algal diets (Macrocystis pyrifera, Gracilaria chilensis, and Ulva lactuca) against an extruded artificial feed during the annual reproductive cycle of E. chloroticus (spring-autumn). Diet switching, cumulative gonad growth and density factors, in addition to gonad and gut indices, gametogenesis and roe colour, were investigated.

Evechinus chloroticus at Elizabeth Island commenced gametogenesis in late winter/spring (July-August 1999) and spawned in early summer (NovemberDecember 1999) with a gonad index of 20.25% and 8.30% respectively. The artificial diet recorded the largest growth in gonad indices (23.15%, 18.83% and 20.81 %) in all three experiments, significantly higher (ANOVA post-hoc LSD; p=0.034) than all other diet treatments and field samples. Of the algal diets, Macrocystis pyrtfera recorded the largest growth in gonad indices (18.16%, 12.96%, and 18.29%), significantly higher (ANOVA post-hoc LSD; p=0.049) than all other algal treatments and end field samples. The G. chilensis and U. lactuca diets produced negligible gonad growth in Experiment 1 and 2. The brightest roe colours were produced on the M. pyrifera and artificial/M. pyrifera diet switch treatments in Experiment 3 during the 'recovery' stage of gametogenesis in Elizabeth Island sea urchins. Low mortality (0.43%; Experiment 3), feeding rates (1gurchin/day artificial diet) and experimental length (9 weeks) suggest the use of sea cages for experimental E. chloroticus gonad enhancement has been realised in this study.