Influence of pH on the Production of Clownfish (Amphiprion percula) and Seahorse (Hippocampus reidi) in Low-Salinity Recirculating Aquaculture Systems
Author: Mario Davi Dias Carneiro (Currículo Lattes)
Advisor: Dr. Luís André Nassr de Sampaio
Abstract
Ornamental aquaculture holds great economic importance and contributes to conservation. However, the production of ornamental fish is not predominantly practiced in coastal areas, making low-salinity recirculating aquaculture systems (RAS) an appealing option. One of the consequences of RAS is water acidification due to the consumption of alkalinity reserves through the nitrification process. The clownfish Amphiprion percula is a small marine ornamental fish widely available in the aquarium trade due to its ease of captive breeding. The seahorse Hippocampus reidi is an ornamental fish also used in traditional Chinese medicine. The reproduction of both species is known and practiced in many regions worldwide. However, the effects of acidic environments on biochemical parameters in ornamental fish are poorly understood. Therefore, the main objective of this thesis is to study the production of seahorse (H. reidi) and clownfish (A. percula) in RAS, evaluating the problems resulting from acute and chronic acidification in seawater (SW, salinity 33) and brackish water (BW, salinity 11). For this, acute experiments (96 h) were carried out: (i) in SW, evaluating the effects of pH levels 5, 6, 7, and 8 on biochemical parameters in A. percula juveniles; (ii) evaluating the same parameters in liver, gills, digestive tract, and muscles of A. percula exposed to the same pH levels in BW and SW; (iii) evaluating the acute effects of pH levels 5, 6, 7, and 8 in BW and SW on H. reidi juveniles; (iv) evaluating the chronic effects (3 and 4 weeks) of pH 6.5 and 8 in BW and SW on H. reidi juveniles; and (v) evaluating the chronic effects (8 weeks) of pH 6.5 and 8 in BW and SW on A. percula, as well as assessing their return to control conditions (8-SW). Acute responses in A. percula revealed greater protein damage in fish exposed to pH 5. The organs of this species respond differently to acidic exposure depending on salinity, with the most affected organs being the gills and liver, which showed reduced GST activity at pH 5-BW and increased lipid damage (TBARS) in the gills at pH 5-SW. Regarding seahorses, acute exposure to acidic environments at low salinity (pH 5-BW) caused greater harm across various stress indicators, showing increased cortisol levels, enzymatic changes (SOD, GST, GPx), and glutathione metabolism disturbances, accompanied by reduced antioxidant capacity (TEAC) and increased lipid peroxidation (TBARS). Moribund fish were also observed at pH 5-BW. Similarly, H. reidi chronically exposed to pH 6.5-BW suffered higher mortality, lower growth, and greater biochemical changes, while the same acidic condition in SW promoted better growth and GSH accumulation. Also during chronic exposure, A. percula showed greater adverse effects under acidic BW conditions, with lower survival and growth, as well as increased protein (P-SH) and lipid (TBARS) damage. At pH 8-BW, the fish presented higher TBARS levels but developed a distinctive and more appealing coloration for the ornamental market, known as the Onyx variety. However, returning these animals to control conditions (pH 8-SW) did not cause additional mortality, and biochemical parameters were considered stabilized after 7 days. Thus, as a general conclusion, it can be stated that for both species, exposure to acidic environments is more harmful under low-salinity conditions.