Abstract
Three microalgae viz., Chlorella ellipsoidea, Scenedesmus obliquus and Spirulina platensis were cultured in three different inexpensive waste media viz., fertilizer factory effluent (FFE), sweetmeat factory waste (SFW) and papaya (Carica papaya) skin powder (PSP). Chlorella ellipsoidea and S. obliquus were isolated from the Bangladesh Agricultural University (BAU) campus pond and S. platensis was used from the stock of the Live Food Culture Laboratory of the Department of Aquaculture, BAU. Chlorella ellipsoidea, S. obliquus and S. platensis were cultured in different concentrations of prepared media from FFE, SFW and PSP with control Bold basal medium (BBM) for C. ellipsoidea and S. obliquus, and Kosaric medium (KM) for S. platensis. Among the different media 50% FFE medium showed significantly (p<0.05) higher growth (in respect to cell number, chlorophyll a, specific growth rate of cell and chlorophyll a, and total biomass) than other media except control for all the three species of microalgae. The chemical oxygen demand (COD), total solids (TS), total suspend solids (TSS) and total dissolved solids (TDS) were found lower after culture of microalgae in all the cases. The physico-chemical parameters of the culture media were found within the suitable range of microalgae culture. The contents of PO4-P and NO3-N increased with the age of culture up to the pick of growth and then decreased. On the other hand in most cases the contents of NO2-N and NH3-N increased up to the last day of culture. In most cases pH was found the maximum at 10th day of culture when the growth was optimum. Proximate composition analysis showed that the cultured algae were rich in protein, lipid and other mineral contents. Protein percentage of S. platensis were significantly (p<0.05) higher than other two species of microalgae. The fingerlings of Barbadoes gonionotus and Hypophthalmichthys molitrix were reared in aquaria by feeding these cultured microalgae (C. ellipsoidea, S. obliquus and S. platensis) in seven different combinations and a control fed on artificial diet for a period of three weeks. In respect of length and weight gain and specific growth rate (SGR, %/day) of fingerlings were significantly (p<0.05) higher when fed on 100% S. platensis than other treatments for both B. gonionotus and H. molitrix. The growth performance of B. gonionotus was comparatively better than H. molitrix. The reared fingerlings were found nutritionally rich. It was concluded that culture of important microalgae might be established in Bangladesh using inexpensive wastes, which ultimately promote culture based aquaculture system and environment will be partially free from pollution.