© 2015 Elsevier B.V. The development of microalgae culture technology has been an integral part of the production of commercially important species in aquaculture. This has been the reason to make great efforts in order to understand several aspects of the microalgae production. The detailed research on monitoring cell growth, which is considered a fundamental part for the use of microalgae in aquaculture, has been, however, overlooked. In this paper, a calibration curve is proposed; correlating the specific absorbance and measured cell density by cell counting (cellsmL<sup>-1</sup>), from four microalgae species important for aquaculture. The final result allows the prediction of cell counting from absorbance using cellsmL-1=β12-4β2β0-Abs12-β1/2β2 which is valid for Abs<β<inf>0</inf>-β<inf>1</inf><sup>2</sup>/(4β<inf>2</inf>). The adjusted determination coefficients (r<sup>2</sup><inf>adj</inf>) were 0.998, 0.995, 0.991, and 0.998 for Chaetoceros calcitrans, Isochrysis affinis galbana (T-Iso), Nannochloropsis gaditana and Phaeodactylum tricornutum, respectively. The results showed that the obtained equations can be used with an error of less than 5% for microalgae densities of up to 1.01×10<sup>7</sup>cellsmL<sup>-1</sup>, 2.11×10<sup>7</sup>cellsmL<sup>-1</sup>, 8.52×10<sup>7</sup>cellsmL<sup>-1</sup>, and 1.67×10<sup>7</sup>cellsmL<sup>-1</sup> in the abovementioned species, respectively. Statement of relevance: A rapid, simple and specific spectrophotometric methodology for biomass measurements of four microalgae species with high importance in aquaculture was developed. The specific wavelength for the maximum absorbance was established for each of the studied species. With the methodology described here, the harvest time will be easier to identify in facilities where these algae are cultured, and can be also easily tested in other monocultures. In addition, a predictive model was satisfactory and useful for a wide range of cell densities yielding a methodology with high potential for automation. A useful tool was developed for cell counting of microalgae in aquaculture.
- Calibration curve
- Cell counting