Low levels of E2 induce synthesis of Vg and Chg even at a concentration of 0.001 μM (Rani et al., 2010 http://link.springer.com/article/10.1007/s10695-009-9332-8). It is well known that Chg is produced earlier at low concentration of E2 and its final product i.e.ZP1 and ZP2 provide structural integrity to the egg membrane. It can be concluded that E2 increases egg quality. But it depends upon the time of exposure to the fish, whether you want to do the experiment at the pre-vitellogenesis phase, vitellogenesis phase or post-vitellogenesis phase.

Exogenous E2 is more often seen as an endocrine disruptor. You see, the reproductive physiology of fish is finely tuned by numerous cross-talking endocrine mechanisms, themselves driven by exogenous factors (temperature, photoperiod, feed quality...). So I would not bet on exogenous hormones to improve the quality of reproduction in fish. In addition, you have great chances to disturb male reproduction.