Growth without diversification: 24 years of stagnant national portfolios in aquaculture

Aquaculture now supplies more aquatic animals than capture fisheries, and its expansion is often assumed to diversify farming. We analyzed national production records compiled by the Food and Agriculture Organization of the United Nations (FAO) for 1950 to 2024. From 2000 to 2024, farmed aquatic animal output tripled (32.5 to 102.7 Mt) and reported species items rose by half (304 to 472), yet national production stayed narrow: in 2024, 62.3% of producing countries (129 of 207) relied on the equivalent of fewer than three equally abundant species items, and countries' diversification was unrelated to their growth (Spearman ρ = −0.05, P = 0.50). Global diversity has not increased since about 2009; outside China it fell by about a quarter (38.9 to 28.9) as countries converged on the same species, while growth shifted toward fed species. Expansion alone has not broadened what countries farm.