Explanation: Gene transfer to fish is generally carried out by microinjection, but other methods are emerging. Fish transgenesis can be used to study gene function.

Explanation: Fish transgenesis can be used to study gene function and regulation, e.g. in model species such as the zebrafish and medaka.

Explanation: Model species such as Danio rerio and Oryzias latipes are used to improve the traits of commercially important species such as salmon and trout.

Explanation: Gene transfer technology in fish has lagged behind that in mammals predominantly due to lack of suitable regulatory elements to control transgene expression.

Explanation: The first transgenic fish carried transgenes driven by mammalian or viral regulatory elements and their performance varied considerably.

Explanation: Attempts to express growth hormone genes in trout initially met with little success and this may have been due to the inability of fish cells to process mammalian introns correctly.

Explanation: Fish are advantageous assay systems because of their fecundity and the fact that fertilization and development are external and the ease with which embryos can be produced.

Explanation: The fertilization and development in fish are external and the ease with which haploid and uniparental diploid embryos can be produced.

Explanation: Like frogs, the injection of DNA into fish eggs and early embryos leads to extensive replication and expression from unintegrated transgenes and hence they can be used for transient assays.

Explanation: Some of the DNA integrates into the genome leading to germline transformation and the production of transgenic fish lines.