The wastewater from fish farming has been used for irrigation and has been tested in the production of seedlings, and can be a sustainable and economical alternative in the midst of the water crisis. The use of seaweed biostimulants for fruit fertilization has been studied by several authors, and these have found an excellent potential and results in the production of quality seedlings. In view of the above, the objective of this work was to evaluate the production of tamarind seedlings irrigated with aquaculture water from the fish farm and fertilized with natural seaweed biostimulant. The work was carried out, from May to October 2016, at the Federal Rural Semi-Arid University (UFERSA), East Campus in Mossoró-RN. The seeds used in the planting of the seedlings came from healthy and mature fruits of a tamarind plant located in the Didactic Orchard of UFERSA. The water used for irrigation of the tamarind seedlings was removed from the fish farming sector, located at the Federal Rural Semi-Arid University (UFERSA), East Campus in Mossoró-RN. The biostimulant used in the fertilization was the seaweed extract of the species A. nodosum. The experimental design used was in randomized complete blocks (DBC) in a 2x5 factorial scheme, with four replications. The first factor was represented by the presence or not of fertilization with biostimulant and the second factor by the concentration of the residual water of the fish culture (0%, 25%, 50%, 75% and 100%). Each experimental unit was represented by 5 seedlings, totaling 200 plants. High concentrations of wastewater from fish farming promote decline in the following evaluated characteristics: Number of leaves, length of the aerial part, total length, dry mass of the root system, dry mass of the aerial part, total dry mass, stomatal conductance and transpiration. Biostimulant of Ascophyllum nodosum at the dose of 4.0 ml L-1 promotes increases in lap diameter, shoot length and dry biomass accumulation of tamarind seedlings.