Study on production strategies for marine aquaculture in China at different scales: a case study of large yellow croaker (Larimichthys crocea)

China is the largest marine fish farming country of the world, contributing greatly to world food security and nutrition. Though yields have been increasing yearly, it is still an open question whether farming strategies on farms of different sizes can achieve optimal economic efficiency. In this study, a dynamic bio-economic model based on the production data from 71 farms in China from 2020 to 2023 was developed to simulate the optimal farming cycle and the initial number of fry to be released for different farm scales, using cage culture of the large yellow croaker (Larimichthys crocea) as an example. This work suggests that producing larger fish is more profitable for farms across three different scales. Under the assumption of a stable and suitable farming environment, and without accounting for other potential risks associated with farming, all three scales of farms tend to achieve higher profits at a 27-month farming cycle. Prolonging the farming cycle could result in losses. Specifically, large and medium-sized farms begin to incur losses by the 32nd month, while small farms start to suffer losses by the 31st month. In the future, it is anticipated that more production risks will be factored in to further validate this perspective. The corresponding recommended initial number of fry is 450,000, 2,240,000, and 39,810,000 for small-, medium-, and large-scale farms, respectively. An excessive initial number of fry is common on farms, resulting in cost losses, especially on small-scale farms. Medium- and large-scale farms are more profitable and risk-resistant than small-scale farms. The study identified the key factors affecting the farm profitability. The price at the farm gate and feed expenditure were the main factors affecting the net profits. The government should assist in improving feeding management practices to reduce feed costs, offer guidance on farming techniques to small-scale farmers, and steer the market to broaden consumption. This theoretical model maximally reveals the profit process of different scales and stages of marine fish farming in China and providing a foundation for further research.