The Eurasian Perch (Perca fluviatilis) is a freshwater fish belonging to the Percidae family, which includes other species of high commercial interest such as the zander and pike-perch (Sander lucioperca).
It is generally reared in closed loop RAS systems or in outdoor ponds, sometimes through a mixed system. Sale takes place when commercial size is reached, corresponding to about 150 g. The main market for this species is represented by the countries of the Alpine area but it is appreciated in many areas for the tastiness of its meat and the compactness of its fillets.
The reproduction of perch in nature occurs in spring, but it is not uncommon for so-called “out of season” reproduction to be carried out in commercial farms. This term refers to a set of operations aimed at obtaining eggs at any time of the year, which considerably benefits planning of operations and optimization of production which can, in this way, be planned ad hoc.
The perch has a unique feature: that of laying eggs joined to each other, thanks to a glycoprotein, to form a structure that is defined as a “ribbon”. The ribbons of the largest females, at the height of their sexual maturity, can reach one meter in length and sometimes even more.
To obtain eggs out of season, the breeding fish are kept in RAS systems dedicated to their exclusive use, where their cycle, consisting of photoperiod and related water temperatures, is modified in such a way as to make “spring” coincide or, better, the warming of the water post wintering period, with the desired time of year for reproduction.
Photo: Out-of-season perch boordstock. Credit: Matteo Capodicasa
The egg incubation period is 140 degree-days. It is therefore necessary to take 10 days at a temperature of 14 °C to complete the maturation of the embryos and determine the hatching of the eggs. The larvae at birth are approximately 6 mm long and are fed with Artemia salina nauplii for about 3 weeks and then weaned with artificial feed.
The perch is a physoclistous fish, meaning that, in adulthood, this species does not have the swim bladder connected with the digestive system. The filling of this apparatus takes place in the first days of the life cycle, when there is a small connection channel. Therefore, it is very important that the young larvae have good access to the water surface, which must be kept clean from any impurities, so that they will be able to swallow a bubble of air through the mouth that will be used to initiate swim bladder development.
Another important consideration to make is related to cannibalism. The perch is a fish that live in shoal but has no qualms about attacking members of the same species if the difference in size allows it (sometimes not even). This inclination tends to disappear as the fish grow but it can represent a big problem in the initial stages of rearing. It is therefore up to the breeder’s skill and ability to make appropriate corrections to the production protocol, applying the appropriate grader aimed at maintaining uniformity of size within the stocks present in the selected farming system.