The present study was aimed to evaluate the suitability of various chemical flocculant–produced algal pastes for milkfish larval rearing. The marine microalga, Tetraselmis suecica, was cultured in 120 days old shrimp (Penaeus vannamei) wastewater for 14 days. Then, the cultured microalga was harvested through four chemical flocculants, viz., ferric chloride (FC), ferrous sulfate (FS), aluminum chloride (AC), and aluminum sulfate (AS). The artificial culture medium (ACM)– and wastewater (WW)-cultured microalga was considered as control. The proximate composition and FTIR analyses of flocculated paste revealed that the flocculants did not make any harm to algae and their properties. The larval rearing experiment lasted for 90 days, and the initial concentration of protein, carbohydrate, amino acids, and fatty acids and antioxidant enzyme activity were analyzed in six Chanos chanos. The FS and ACM utilized CC exhibited higher survival (P < 0.05), length (P > 0.05), and weight (P > 0.05), whereas the growth rates (P < 0.05) were higher in AS used CC. Among the treatment, no significant variations (P > 0.05) were found in proximate compositions (protein, carbohydrate), antioxidant and metabolic enzymes, digestive enzymes, and non-enzymatic antioxidants, and significant variations (P < 0.05) were found in lipid accumulation. The glutamic acid, aspartic acid, leucine, and lysine were the dominant amino acids, and palmitic acid, oleic acid, linoleic acid, and stearic acid were the dominant fatty acids in milkfish larvae fed with various algal flocculates. Histology studies suggest that the milkfish fed by flocculated paste using flocculants did not cause any harm to fish parts and their digestive ability. Thus, the results suggest that the flocculation of microalga by chemicals did not exert much toxicity on the feeding of algal pastes by the animals and it is recommended to use such algal-pastes in large-scale level in the future.

Graphical abstract

中文翻译：

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废水养殖 Tetraselmis suecica 用于养殖 Chanos chanos 的生产和使用：化学絮凝藻糊对遮目鱼幼虫生长、存活和近似成分优势的评估

本研究旨在评估各种化学絮凝剂生产的藻糊对遮目鱼幼虫饲养的适用性。海洋微藻Tetraselmis suecica在 120 日龄对虾 ( Penaeus vannamei ) 中培养) 废水 14 天。然后，通过四种化学絮凝剂，即氯化铁（FC）、硫酸亚铁（FS）、氯化铝（AC）和硫酸铝（AS）收获培养的微藻。人工培养基（ACM）和废水（WW）培养的微藻被认为是对照。絮凝糊的近似组成和 FTIR 分析表明，絮凝剂对藻类及其特性没有任何危害。幼虫饲养实验历时90天，对6个Chanos chanos的蛋白质、碳水化合物、氨基酸和脂肪酸的初始浓度和抗氧化酶活性进行了分析。使用 CC 的 FS 和 ACM 表现出更高的存活率 ( P  <  0.05 )、长度 ( P  > 0.05）和体重（P  >  0.05），而 AS used CC 的增长率（P  <  0.05）更高。各处理中，近端成分（蛋白质、碳水化合物）、抗氧化代谢酶、消化酶、非酶类抗氧化剂差异不显着（ P  >  0.05 ），差异显着（ P  <  0.05 ）) 在脂质积累中发现。以谷氨酸、天冬氨酸、亮氨酸和赖氨酸为主要氨基酸，棕榈酸、油酸、亚油酸和硬脂酸是喂食各种藻类絮凝物的遮目鱼幼虫的主要脂肪酸。组织学研究表明，使用絮凝剂的絮状糊料喂养的遮目鱼不会对鱼体部位及其消化能力造成任何伤害。因此，结果表明，化学物质对微藻的絮凝对动物喂食藻糊没有太大的毒性，建议将来大规模使用这种藻糊。

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