**1. Introduction**

With the increasing demand for high-quality protein, it was estimated that global fish production will increase by 32% by 2030 compared to 2018 [1,2]. However, in recent years, due to adverse factors such as limited space resources, environmental deterioration, excessive aquaculture density, and frequent disease outbreaks, the inland and nearshore aquaculture space has been seriously restricted [3,4]. To reduce the impact of aquaculture on land-based and nearshore areas, it was imperative to expand the aquaculture space. Enclosed aquaculture vessel was a new offshore aquaculture method in recent years. It was expected to be an important way to develop offshore aquaculture [5,6].

The development of offshore areas can be used as an important space for fish farming in the future. Offshore seas have the advantages of a wide area, good water quality, and few pollutions and pathogenic microorganisms [7]. Currently, many practical activities for offshore aquaculture have been carried out in China, Norway, Scotland, Korea, Japan,

**Citation:** Yu, Y.; Huang, W.; Yin, F.; Liu, H.; Cui, M. Aquaculture in an Offshore Ship: An On-Site Test of Large Yellow Croaker (*Larimichthys crocea*). *J. Mar. Sci. Eng.* **2023**, *11*, 101. https://doi.org/10.3390/ jmse11010101

Academic Editor: Ka Hou Chu

Received: 2 December 2022 Revised: 26 December 2022 Accepted: 27 December 2022 Published: 4 January 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

and other countries [8–11]. Studies have shown that offshore aquaculture can effectively improve the survival and growth of salmon and bluefin tuna and reduce the possibility of fish disease [12–14]. At the same time, offshore areas have relatively harsh environmental conditions, such as large wind waves and currents, which may damage the breeding equipment and fish health [15,16]. Therefore, offshore aquaculture needs to improve the requirements of technology, capital, operation, and other aspects.

As a new model of closed aquaculture, the relevant research data on the aquaculture ship was very scarce. It was reported that only Türkiye (Turkey) transformed a bulk carrier into an enclosed aquaculture vessel and carried out the breeding test of rainbow trout. The initial average body weight was 25.0 ± 2.7 g and reached 3.7 ± 0.4 kg after 11 months. The feed conversion ratio (FCR), specific growth rate (SGR), and breeding density were 1.1 ± 0.1, 1.51 ± 0.3%/d, and 101 ± 2.1 kg/m3, respectively [17]. Large yellow croaker is the main mariculture fish in China, and its production ranks first in mariculture all year-round. Due to its flavor, high flesh quality, and nutritional value, large yellow croaker has a large market space [18]. Large yellow croaker resources almost disappeared from the end of the last century to the current output of more than 250,000 tons, which mainly benefitted from the development of artificial aquaculture technology [19]. However, knowledge about the growth performance and nutritional composition of large yellow croaker that are reared in ships and cages for a short period is limited. Therefore, this experiment takes large yellow croaker as the target animal to explore whether the closed aquaculture system can be used in fish culture, determine the growth performance of large yellow croaker under this culture mode, and analyze the conditions that are suitable for large yellow croaker culture under this mode. In addition, if the platform can be used in offshore areas, the results of this study can establish a set of aquaculture technology standards, such as seed transfer and environmental control, and provide a scientific basis for the establishment of large yellow croaker and other fish.
