Of course there are common genetic deformities.
But alternatively.....young fish brought up in different water type than they are evolved over centuries to live in can create developmental deformities.
Fish evolved to live in mineral rich water, can develope deformities in soft mineral poor water.
Fish eveolved over millennia to live in soft, low pH water often develope poorly and have health problems in hard water.
Rams are notorious for this sensitivity.
Although Bolivian Rams (M altispinosa) are considered less sensitive than their northern counterparts, even a slight tweak in pH is known to skew sex ratios.
Consider, if a few simple degrees up or down, such as 6.4 to 6.8 can do that with gender, what trying to raise fry in pH of 7.8 or higher can do.