Integrated System of Red Seaweed Kappaphycus alvarezii (Rhodophyta, Solieriaceae) and Clownfish Amphiprion ocellaris (Perciformes, Pomacentridae): An Experimental Study ^†

This study aimed to analyse the integrated system of red seaweed Kappaphycus alvarezii and clownfish Amphiprion ocellaris. Experiments were performed in a 45 L aquarium under the following controlled conditions: temperature 22 °C, dissolved oxygen 5 mg/L, salinity 30, and photoperiod 12 h light. There were 10 fish per aquarium, fed with commercial food. Four treatments were tested (three replicates per treatment): (1) only fish (control); (2) fish with 250 g seaweed; (3) fish with 500 g seaweed; and (4) fish with 750 g seaweed. Weekly seaweed and fish were weighed and measured, and ammonia (NH₃), nitrite (NO₂), nitrate (NO₃⁻), phosphate (PO₄³⁻), and phosphorus (P) were analyzed. The total weight (g) (TW) of fish differed over time (F = 0.00) and between treatments (F = 2.84; p = 0.03). Higher TW (±0.75 g) occurred in treatment 3 and after 14 days did not significantly differ from the end of the experiment (p < 0.01). The total length of fish (cm) did not differ significantly over time (F = 0.64; p = 0.66) or between treatments (F = 0.34; p = 0.79). The relative growth rate of seaweed (RGR) did not differ over time (p > 0.12). There was a significant interaction between the nutrients present in the water by treatment and time (F = 3.59; p = 0.00). The nutrient removal efficiency (NRE) of NH₃ and NO₂ was higher in treatments 3 and 1, respectively, reaching ±30% at 14 days (p < 0.001), and from the 21st day of the experiment, the values were close to zero, with no significant difference between treatments up to 35 days (p > 0.90 for both). The NRE of NO₃⁻ increased by 2% at 28 days of the experiment, with no significant difference between treatments (p > 0.07). The NRE of P was ±25% at 14 days and was not different between treatments 1 and 2. The NRE of PO₄³⁻ reached 14% at 21 days for treatments 1, 2 and 3 (p < 0.001). The control showed lower values for the NRE of NH3, NO₃⁻, P, and PO₄³⁻ compared to the treatments, but the NRE of NO₂ increased in 14 days. It is concluded that a greater abundance of K. alvarezii helps in water quality and contributes to the total weight of clownfish between 14 and 21 days.