Abstract
This study is aimed at revealing the dietary protein requirement for gonad production in the sea urchin Mesocentrotus nudus, with consideration of protein leaching from diets during seawater immersion. Feeding trials were performed on M. nudus using two diet types with low capacities for protein leaching: starch diets (STG) containing 0–40% gluten in 10%, 5%, and 4% increments (experiments 1–3) and alginate diets (ALG) containing 5–25% gluten in 5% increments (experiment 4). The protein content in the diets was determined after they were immersed in seawater for 24 h or 72 h. The gonad indices of urchins fed STG with 11.4–19.3% protein were significantly higher than those fed STG with 7.8% protein. The protein requirement was estimated to be 12% based on a broken-line regression analysis of urchins fed STG in experiments 1–3. In experiment 4, the gonads became larger as dietary protein content increased from 4.5% to 12.0%, and the sizes were similar to those of urchins fed ALG with 12.0–21.1% protein. The estimated value of 12% was much lower than that reported previously (>20%), indicating that the protein requirement for sea urchin gonad production is modest when the protein-leaching problem is addressed.
Highlights
To select ingredients for diets with high shape stability and low protein leaching during seawater immersion, a seawater immersion test was performed with 16 prepared diets that were formulated to examine three experimental factors: (1) binder source, (2) protein source, and (3) binder concentration (50%, 15%, and 5%; percent dry weight of all dietary components) (Table S1)
The present study investigated the dietary protein requirement for M. nudus gonad production by addressing the problem of dietary protein leaching
In the feeding trials using STG and alginate diets (ALG) diets with low disintegration and protein leaching, the dietary protein requirement for the gonad production of M. nudus adults was estimated to be approximately 12%, which is much lower than that previously reported for various sea urchin species
Summary
The global consumption of fish and shellfish increased from 69 million tons in 1991 to 132 million tons in 2013 [1], and it is predicted to reach 178 million tons by 2028 [2]. The annual average price of sea urchin gonads at the Tokyo Metropolitan Central Wholesale Market, the largest sea urchin market in the world [4], has nearly doubled over the past decade [5]. The import of live, fresh, or chilled sea urchins to European and Oceanian countries has been occurring since 2012 [6], indicating that the worldwide demand for sea urchins has been increasing. A decrease in world sea urchin landings from 109,736 tons in 1995 to 75,637 tons in 2019 [7] because of stock depletion caused by overfishing [8] has promoted the need to produce hatchery-raised urchins in aquaculture systems [9, 10]. Sea urchins densely distributed on “barrens” (e.g., [11, 12]), where communities of crustose coralline red algae without erect macrophytes occur in subtidal rocky seafloors, exhibit decreased growth rate and have small gonads with inferior quality (e.g., [13, 14]). Utilization of barren individuals of Mesocentrotus nudus in Northern Japan [15–17], Heliocidaris erythrogramma in Australia
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