The use of stable isotope ratios δ ¹³ C and δ ¹⁵ N to track the incorporation of Ulva and other important dietary ingredients into the gonads of the sea urchin Tripneustes gratilla

Abstract

In this study, we demonstrate how stable carbon (C) and nitrogen (N) isotope analysis can be used to estimate the allocation of specific dietary ingredients, incorporated into four artificially formulated feeds supplemented with varying amounts of dried seaweed Ulva armoricana (0, 50, 150 and 200 g/kg), to the production of gonads by Tripneustes gratilla over a 20‐week growth trial. Results indicate that U. armoricana is an important dietary ingredient for gonad production, accounting for an average of 37.33 ± 1.03% of the isotopic signal recorded for gonads at the end of the growth trial. This is significantly more than fish meal and soya, which only contributed an average of 11.40 ± 1.81 and 3.80 ± 0.09%, respectively, of the isotopic signal of the gonads. Maize and wheat each account for almost 25% of all the dietary ingredients used to formulate the feeds, but their relative contribution to gonad production only averaged 8.55 ± 0.58 and 3.80 ± 0.05%, respectively, among the diets. This indicates that, at least for gonad development, these ingredients may not be required at such high levels. These findings support previous data on the importance of Ulva in abalone and urchin diets, and demonstrate the value of stable isotope analysis for assessing the contribution of specific dietary ingredients in new feed formulations, particularly where growth of specific tissues is being investigated.

Assessing the potential of the unexploited Atlantic purple sea urchin, Arbacia punctulata, for the edible market

“…The tanks (n = 10 sea urchins per replicate) were randomly allocated to baseline sampling or one of five diet treatments (3 replicate tanks per treatment and baseline group). One diet comprised of Ulva lactuca ("Ulva") was used due to various Ulva species having shown to act as a feeding stimulant and enhance gonad growth and quality in sea urchins when added as an additive to pelleted feeds (Cyrus et al, 2015a;Cyrus et al, 2015b;Shpigel et al, 2018;Cyrus et al, 2019). Due to its abundance in coastal areas around the globe U. lactuca may be a cheap and easily available alternative to other diets for raising sea urchins and is easily dried as a supplement for pelleted feeds (Cyrus et al, 2014).…”

Natural Food Intake and Its Contribution to Tambaqui Growth in Fertilized and Unfertilized Ponds

“…However, this technique does not reveal the contribution of each kind of feed to fish growth because part of the eaten feed is not assimilated. Stable isotope analysis is a tool for quantifying dietary support of fish growth among the ingested feed items with distinct isotope content, since the isotopic compositions of animal tissues resemble their diets [26][27][28][29][30][31]. Since formulated diet is the main cost of production in fish farms [3], understanding its utilization by fish and how it can be replaced or complemented by natural food would help to improve feeding strategies and decrease production costs.…”

The effect of fresh seaweed and a formulated diet supplemented with seaweed on the growth and gonad quality of the collector sea urchin, Tripneustes gratilla , under farm conditions

“…These authors have also demonstrated that fresh as well as dried U. rigida incorporated into formulated feed enhances the chemosensory properties of the feed, significantly improving feed conversion ratio (FCR), consumption and the digestible protein and energy intake by urchins (Cyrus et al., 2013). Furthermore, U. rigida in formulated feeds has also been shown to be actively incorporated into the gonad themselves, contributing to tissue composition (Cyrus, Bolton, & Macey, 2019). Cyrus, Bolton, and Macey (2015) divided the grow‐out phase of T. gratilla for full life cycle cultivation into a somatic phase and gonadal development phase.…”