SOLID EARTHWORM COMPOST USED AS PHYTOPLANKTON PROMOTER IN A WHITE SHRIMP Litopenaeus vannamei EXPERIMENTAL CULTURE.

In Mexico the annual shrimp aquaculture rate production is growing, and thus demands more feeding inputs, representing ~50% of the operative costs (CONAPESCA, 2011). In shrimp culture, fertilization is needed to improve primary productivity (Clifford, 1997). Among organic fertilizers, Eisenia foetida humus is considered as a great promoter for plankton growth, helping to develop these aquatic organisms (Chakrabarty, 2008). The aim of this study was to analyze and evaluate different earthworm humus as phytoplankton promoters. Six treatments were evaluated, in 12 L tanks with salt water (10 ups),  zero water exchange and the following initial doses: T1 (blank), T2 (Urea) 0.45g·L^-1, T3 (solid humus- cattle manure worm compost[WC]) 0.5g·L^-1, T4 (liquid humus- cattle WC) 0.1L·L^-1, T5 (solid humus- vegetable wastes WC) 0.5g·L^-1 and T6 (liquid humus- vegetable wastes WC) 0.1L·L^-1, with three replicates for each one. The doses were, thereafter, reduced by half.

The experiment lasted 33 days. Samples were quantified and identified to group level. Water quality parameters were not constant during the experiment and had significant difference (P>0.05) between oxygen and pH treatments. For phytoplankton quantity, treatment T6 had the highest number of cells with 551, 500 cell ml^-1, but had no significant difference with T5 who had 500, 650 cell ml^-1 (Figure 1). It had significant differences with other treatments. Four different phytoplankton groups: diatoms, chlorophytes, cyanophytes and nanoplancton, were identified. Some studies suggest that diatoms and chlorophytes are an important food resource for juvenile shrimp. Organic fertilizers improved water quality and enhanced phytoplankton production; we observed that none identified nanoplankton had significant differences with diatoms, chlorophytes and cyanophytes. We found that shrimp reared with the organic fertilizer had the best survival (Table 1), but the lowest final weight. The use of vermicompost as a nutrient promoter, in any of its forms, (solid and liquid) could be an inexpensive option as an organic fertilizer, in the shrimp aquaculture industry as well as for other species.