Assessing the viability of commercial media for the mass culture of <i>Chaetoceros muelleri</i>

Abstract

The microalgae <i>Chaetoceros muelleri</i> is considered a highly nutritious feed for the cultured larvae of the tropical sea cucumber <i>Holothuria scabra</i>. Due to the cost of analytical grade culture media used in the production of <i>C. muelleri</i>, there is a need to evaluate cheap alternative commercial media to decrease the cost of producing quality live microalgal food. In this study, two different indoor batch culture systems (1 L glass bottles and 10 L plastic carboys) were used to evaluate the effectiveness of two conventional (modified F/2 and Walne’s) and one commercial (Epizyme AGP complete) microalgal culture media. Results of the 1 L glass bottle experiment showed that the peak cell density of <i>C. muelleri</i> in AGP (1,241 ± 116 x 10⁴ cells ml^-1) was not significantly different from the modified F/2 (1,584 ± 41 x 10⁴ cells ml^-1) and Walne’s medium (1,319 ± 162 x 10⁴ cells ml^-1) (Kruskal-Wallis test, p=0.78). Likewise, in the plastic carboy experiment, the maximum cell density of <i>C. muelleri</i> in Walne’s medium (750 ± 144 x 10⁴ cells ml^-1) and F/2 medium (653 ± 79 x 10⁴ cells ml^-1) were higher, but not significantly different from AGP (496 ± 184 x 10⁴ cells ml^-1) (Kruskal-Wallis test, p=0.43). The highest growth rate in the glass bottle cultures was the modified F/2 (0.38 div day^-1), while AGP was the lowest (0.34 div. day^-1). On the other hand, in carboy culture, AGP was higher (0.17 div.day-1) compared to modified F/2 (0.15 div. day^-1) and Walne’s medium (0.13 div. day^-1). The exponential growth phase was similar in the glass bottles, while in the carboy, the exponential phase was reached at a shorter time in the AGP treatment than those in the modified F/2 and Walne’s media. The findings showed that AGP medium is an adequate alternative to replace the conventional media (modified F/2 and Walne’s) during the secondary stock culture for <i>C. muelleri</i>. The viability of using cheaper and more readily available commercial AGP media for the indoor culture production of <i>C. muelleri</i> can contribute to cost-effective scaling-up of the hatchery production of quality <i>H. scabra</i> larvae and early juveniles.