Science Centres: Fisheries

Strangely enough, eels get to ‘choose’ their sex, depending on environmental factors, and there is a major imbalance in New Zealand’s eel populations – too many males.

Shortfin male eels seldom exceed 200 g. This can be a problem for eel farming, because high densities favour production of almost 100% males, but the good markets are mainly for eels over 200 g, which tend to be female. Eels are also highly valued by Māori as a customary food species, and generally the eels of choice are even bigger – over 500 g. Male longfins grow to 700 g, but are less likely to be farmed.

Manipulating sex ratios in favour of females has the potential to increase eel production in aquaculture and to buffer natural populations against fishing pressure. NIWA is continuing research into how this could be done.