The Marine Science Institute, University of the Philippines, Diliman, Quezon City
The microalgae Chaetoceros muelleri is considered a highly nutritious feed for the cultured larvae of the tropical sea cucumber Holothuria scabra. Due to the cost of analytical grade culture media used in the production of C. muelleri, 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 C. muelleri 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 C. muelleri 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 C. muelleri. The viability of using cheaper and more readily available commercial AGP media for the indoor culture production of C. muelleri can contribute to cost-effective scaling-up of the hatchery production of quality H. scabra larvae and early juveniles.