Growth performance and nutritional composition of Hemifusus ternatanus under artificial culturing conditions

Highlights

• Cultured whelks showed high rates of growth during the first two years post-hatching.

• Cultured whelks contained higher levels of fat and ash than wild whelks.

• No significant differences in amino and fatty acid composition were observed between the cultured and wild whelks.

• Both the cultured and wild whelks contained high levels of flavor-enhancing amino acids.

• The levels of 18:1n-9c and 22:5n-3 were higher in cultured whelks.

Abstract

Juvenile Hemifusus ternatanus were cultured in a double-layer culturing system for 186 weeks in order to assess growth performance. The growth rate of H. ternatanus under artificial culturing conditions was high during the first 137 week post-hatching, followed by a period of relatively slower growth. The shell of the cultured sub-adult whelks was shorter and thicker than that of the wild individuals with same weight. The proximate, amino acid and fatty acid compositions of H. ternatanus foot muscles were analyzed to compare the quality of cultured and wild whelks. Both the cultured and wild H. ternatanus contained high levels of flavor-enhancing amino acids. No significant difference was observed in protein content, moisture content or amino acid composition. The cultured whelks contained significantly higher levels of fat and ash (P < 0.05). The total saturated, monounsaturated, and polyunsaturated (PUFA) fatty acids were statistically similar between the cultured and wild groups; however, there were significant differences in the content of individual of fatty acids between the two groups, including 17:0, 16:1, 18:1n-9c, 18:2n-6t, 20:4n-6, 22:5n-3, 22:6n-3, and n-6 PUFAs (P < 0.05). The fatty acids 21:0, 15:1, 22:1n-9, 18:2n-6c, and 18:3n-3 were detected in the cultured H. ternatanus only. On the contrary, 18:1n-9t was detected only in the wild H. ternatanus. This study provides novel information regarding the growth and composition of cultured H. ternatanus which will be helpful for the development of aquaculture practices for this species.

Statement of Relevance

This manuscript provides new findings which should be of interest to readers involved in the reproduction and aquaculture of gastropods. H. ternatanus is a marine whelk with agreeable taste and is a potential candidate species for aquaculture. Aquaculture production of H. ternatanus is increasing due to its high market price and the depletion of natural stocks. There is currently no information regarding the nutritional composition of cultured H. ternatanus compared to its wild counterpart. The results of this study will help consumers better understand the nutritional value of cultured whelks and provide aquaculturists with important information for the development of formulated feeds.

Introduction

Hemifusus ternatanus is a predatory marine whelk with a shell that can reach up to 40 cm in length that inhabits the area from the eastern and southern coast of China to Japan (Phillips and Depledge, 1986). These whelks are sold as a luxury food items in markets at a price that ranges from 60 to 90 euros per kilogram. Due to high market demand and prices, an increasing number of whelks are being captured by trawlers. Overfishing has resulted in the severe depletion of natural H. ternatanus stocks, increasing the importance of artificial breeding and aquaculture of this species (Xu et al., 2006).

An understanding of the growth performance of a species is important for the development of aquaculture practices. Although some studies have investigated prey preference (Morton, 1986a), the reproductive system (Cao et al., 2010), artificial breeding (Hong, 2010) and juvenile growth (Xu et al., 2009) of H. ternatanus, the culturing of this species has been limited to the larval and juvenile stages. In a previous study, H. ternatanus juveniles fed live clam grew at a high rate of over 1 cm per month (Tang et al., 2012a, Tang et al., 2012b), but little is known about the growth of sub-adult and adult individuals.

H. ternatanus is a highly specialized predator of bivalves, similar to the related species Hemifusus tuba, which may be explained by its relatively stable tropical environment and predictable food supply (Morton, 1985). Under laboratory conditions, juvenile H. ternatanus were found to prefer live Meretrix meretrix (Tang et al., 2012a, Tang et al., 2012b), which is expected to be different from its natural prey items. Diet has been shown to have an impact on nutritional composition and taste (Prato et al., 2010, Woodcock and Benkendorff, 2008). Besides genetic basis, the quality of seafood products is also dependent on the characteristics of environment (Orban et al., 2007). However, information regarding the nutritional composition of H. ternatanus cultured under artificial conditions is not currently available. In order to develop methods for the profitable commercial production of H. ternatanus, it is necessary to understand the growth and nutritional value of artificially-cultured whelks.

The aim of this research was to study the growth performance of cultured juvenile H. ternatanus, to assess its suitability as an aquaculture species. This research also represents the first attempt to evaluate the differences in amino acid and fatty acid profiles between wild and cultured H. ternatanus, which will be helpful for the development of formulated feeds for this species.