First report of Spirulina sp. performance in wastewater of Cromileptes altivelis aquaculture in Indonesia

Indonesia is one of the countries with the most significant grouper production in the world. One of the groupers that are widely cultured in Indonesia is the humpback grouper (Cromileptes altivelis). Unfortunately, humpback grouper aquaculture activities cause waste. The waste can produce hydrogen sulfide, orthophosphate, and ammonia, which is toxic to aquatic animals. One way to treat the waste is by using Spirulina sp., which is utilizing organic material from humpback grouper waste to support its growth. The purpose of this study was to identify its performance in reducing water quality parameters to tolerance level. It was also to examine the growth of Spirulina sp. on laboratory-scale culture in the humpback grouper nursery media with a varying degree of waste. The study design used was a Completely Randomized Design (CRD) with four treatments and three replications, A (100%), B (75%), C (50%), and D (25%) humpback grouper nursery waste as culture media. The parameters calculated include population density, nitrate, orthophosphate, pH, temperature, salinity, and light intensity. The results showed that Spirulina sp. could reduce nitrate and phosphorus in water up to 89.78% and 84.34% of the waste. Spirulina sp. could maintain all water quality to be following the standards for fish farming again. The utilization of humpback grouper nursery waste at a concentration of 25% has a significant effect on the population growth of Spirulina sp. on laboratory scale culture.