**5. Activating solutions**

By having a limited supply of ATP accumulated in the mitochondria [30], the motility duration in freshwater fish spermatozoa is greatly reduced. Motility is a variable that significantly alter the sperm's ability to fertilize the oocyte [31]. Therefore, the use of balanced osmotic media with substrates that can provide energy to the sperm is desirable [23, 32, 33]. The activating solution may also assist in the reduction of osmotic shock, which is a causative effect of damage in sperm cells [34, 35].

Examples of the use of activating solutions in Brazilian research can be found for *R. quelen* semen [23] using a solution composed of fructose, and for *Pseudoplatystoma corruscans* semen [7] using 1% NaCHO3 solution. For scale fish, the use of solutions based on NaCl (0.29%) and NaHCO3 (1%) are shown to have better results [8].

It is noticed that the use of activating solutions is still not as common in Brazil and the previous studies are focused on the use of solutions based on salts or sugars. Fundamentally, future Brazilian researches should explore the biochemical composition of seminal plasma and ovarian fluid. This knowledge will be instrumental in building a successful activating solution.
