Identification of caviar from increasing global aquaculture production — Dietary capric acid as a labelling tool for CITES implementation in caviar trade

Abstract

Sturgeon (Acipenseridae) have been subjected to intense fisheries pressure due to their highly-priced eggs. Despite the fact that all 27 species are highly endangered and have been listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), regulating international trade, illegal catches still continue to threaten wild populations. In trade, the product is suspected to be camouflaged as caviar from aquaculture origin. Thus, tools to discriminate wild and aquaculture products have to be developed to enforce CITES regulation and thereby allow for the development of the aquaculture industry. Here, the feasibility to use food additives, namely fatty acids and vitamin E, is assessed for labelling caviar from aquaculture origin. Farmed female sterlet ( Acipenser ruthenus) were fed on a diet supplemented with alpha-tocopherol, caprylic and capric acid at 15, 4 and 20 mg/g respectively. Marker concentrations in the caviar were determined from biopsies sampled via micro-incisions over a period of 90 days (0 d, 10 d, 60 d and 90 d) and compared to a control fed on a diet supplemented with 39 mg/g sunflower oil. To address the question whether the effectiveness in using the markers is dependent on strict timing with regard to gonad development and maturation, maturing (early vitellogenesis, 4 year old fish) and mature (late vitellogenesis, stage IV–V) females were studied. The latter represent fish that were ready to be used for caviar production. Neither alpha-tocopherol nor caprylic acid accumulated in the caviar and concentrations quantified by GC–MS were below the detection limit (< 0.005 mg/g). In contrast, capric acid was detected as early as 10 d after the onset of the feeding trial at concentrations between 0.01–0.03 mg/g in maturing as well as mature ovaries. Capric acid would therefore provide a cheap and easy-to-assess tool for labelling caviar from aquaculture, thereby allowing its utilization as an identification system under CITES as recently requested recently by the IUCN Sturgeon Specialist Group.