Bluefin tuna sperm production is hastened by surrogacy in small Euthynnus.

Pacific bluefin tuna (Thunnus orientalis) remains heavily depleted due to overexploitation. Aquaculture and stock enhancement based on artificial seedlings could be effective solutions to this problem. However, widespread adoption of seedling production is limited because spawning in captivity of bluefin tuna, a large pelagic top predator, requires much space, time, cost, and labour. To downsize and shorten their generation time, here, we show that xenogeneic germ cell transplantation enables a surrogate production of functional bluefin tuna sperm in hybrid little tuna (genus: Euthynnus), which attain sexual maturity at a smaller body size and shorter time. Intraperitonially transplanted bluefin tuna germ cells migrate towards and are incorporated into the gonads of little tuna larvae. These recipients produce functional donor-derived bluefin tuna sperm at a mere 8 months of age and 1 kg of body size. This result represents an advance toward compact, low-cost, and time-efficient seedling production that will improve the efficiency of bluefin tuna aquaculture.