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This review discusses the new biotechnological tools that are arising and promising for conservation and enhancement of fish production, mainly regarding the endangered and the most economically important species. Two main techniques, in particular, are available to avoid extinction of endangered fish species and to improve the production of commercial species. Germ cell transplantation technology includes a number of approaches that have been studied, such as the transplantation of embryo-to-embryo blastomere, embryo-to-embryo differentiated PGC, larvae to larvae and embryo differentiated PGC, transplantation of spermatogonia from adult to larvae or between adults, and oogonia transplantation. However, the success of germ cell transplantation relies on the prior sterilization of fish, which can be performed at different stages of fish species development by means of several protocols that have been tested in order to achieve the best approach to produce a sterile fish. Among them, fish hybridization and triploidization, germline gene knockdown, hyperthermia, and chemical treatment deserve attention based on important results achieved thus far. This review currently used technologies and knowledge about surrogate technology and fish sterilization, discussing the stronger and the weaker points of each approach.

This work was aimed at developing an effective procedure to obtain sterile ideal host fish in mass scale with no endogenous germ cells in the germinal epithelium, owning permanent stem-cell niches able to be colonized by transplanted germ cells in surrogate technology experiments. Thus, triploids, diploid hybrids, and triploid hybrids were produced. To obtain hybrid offspring, oocytes from a single Astyanax altiparanae female were inseminated by sperm from five males (A. altiparanae, A. fasciatus, A. schubarti, Hyphessobrycon anisitsi, and Oligosarcus pintoi). Triploidization was conducted by inhibition of the second polar body release using heat shock treatment at 40 °C for 2 min. At 9-months of age, the offspring from each crossing was histologically evaluated to access the gonadal status of the fish. Variable morphological characteristics of the gonads were found in the different hybrids offspring: normal gametogenesis, gametogenesis without production of gametes, sterile specimens holding germ cells, and sterile specimens without germ cells, which were considered "ideal hosts". However, only in the hybrid derived from crossing between A. altiparanae and A. fasciatus, 100% of the individuals were completely sterile. Among them 83.3% of the male did not present germ cells inside germinal epithelium, having only somatic cells in the gonad. The other 16.7% also presented spermatogonia inside the niches. Such a methodology allows the production of sterile host in mass scale, opening new insights for application of surrogate technologies., (Copyright © 2017 Elsevier Inc. All rights reserved.)

In fish with external fertilization, sperm must reach the oocyte through the micropyle to enter the cytoplasm. Fertilization success is then influenced by characteristics of oocytes or sperm. In this study, we evaluated oocyte morphology and sperm motility parameters and their effects on the inseminating dose in a teleost fish Astyanax altiparanae. Interestingly, we found one of the lowest yet described inseminating doses in teleosts (2390 spermatozoa oocyte-1 ml-1). Such a fertilization efficacy may be explained by the long duration of sperm motility (>75 s), the small oocyte diameter (695.119 µm), large micropyle diameter (7.57 µm), and the presence of grooves on the oocyte surface that guides spermatozoon to the fertilization area. Additionally, we have described for the first time a structure that combines grooves on the chorion surface and a ridge in the micropylar area.

The aim of the present study was to establish a protocol of sperm cryopreservation in Misgurnus anguillicaudatus and verify the applicability of the obtained protocol in other loach species. We evaluated the following parameters: inseminating dose, thawing temperatures (20, 25 and 30 degrees C for 10s), extenders (loach or cyprinid extenders), internal cryoprotectants (dimethyl sulfoxide (DMSO), dimethylacetamide (DMA), glycerol (Gly), ethylene glycol (EG), and methanol (MeOH) at 0, 5, 10 and 15%), external cryoprotectants (bovine serum albumin 1 and 2%; sucrose 0.5 and 1%; glucose 0.5 and 1%; glycine 0.5 and 1%), activating solutions (distilled water, dechlorinated tap water, 25mM NaCl and 50mM NaCl), and hatchability of the eggs when fertilized with fresh or cryopreserved sperm. After the evaluation of these parameters, we optimized the cryopreservation using the following procedure: thawing temperature at 25 degrees C for 10s; loach or cyprinid extenders; methanol at 10 or 15% as internal cryoprotectants; glycine 0.5% or bovine serum albumin 1% as external cryoprotectants and 50mM NaCl for sperm activation. Using this procedure, the fertilizability of the post-thawed sperm was 47% in comparison to the fresh sperm, at the minimum inseminating dose (687.65 spermatozoa egg(-1)mL(-1)). Based on this protocol, sperm from other loach species Lefua nikkonis, Misgurnus mizolepis and Barbatula toni were cryopreserved successfully.