Testis transplantation in male rainbow trout (Oncorhynchus mykiss)

The objective of the present study was to establish a procedure for the tra nsplantation of an intact testis from one male rainbow trout (Oncorhynchus mykiss) to another individual and evaluate the reproductive function of the transplanted testis at sexual maturity. Isogenic (cloned) male rainbow tro ut were produced by crossing a completely homozygous male (YY) with a homoz ygous female (XX) to eliminate any problem of tissue rejection. Transplanta tion was performed on four pairs of sexually immature animals (n = 8); each served both as a donor and recipient. The left testis was removed by makin g a ventral midline incision to expose the body cavity and gonads. The left testis was disconnected at the anterior and posterior points of attachment and transferred to the recipient fish where it was placed in position adja cent to the pyloric cecae. The right testis was left intact. after 4 wk, th e fish were injected (i.p.) twice weekly for 8 or 9 wk with salmon pituitar y extract (1.5 mg/kg) to induce precocious sexual maturation. A similar num ber of untreated fish were maintained as controls. Following this treatment , all the fish were killed, and the right (intact) and left (transplanted) testes were removed, weighed, and sampled for sperm. Although the mean weig hts of the left, transplanted testes were significantly (P < 0.05) smaller than the intact testes (transplants = 1.2 g; intact = 3.9 g), transplanted testes were present in all animals, had increased in mass, and were sexuall y mature containing sperm. The mean fertility, as measured by the proportio n of eggs completing first cleavage, of sperm derived from transplanted tes tes (92%) was no different from the sperm obtained from intact testes (84%) . Similarly, there was no difference in the number of embryos attaining the eyed stage of development, after 18 days of incubation, that were derived from transplanted (84%) or intact testes (85%).