Le Cren, E.D. (1951) The length-weight relationship and seasonal cycle in gonad weight and condition in the perch (Perca fluviatilis). J. Anim. Ecol., pp. 201-219
| Species | Development state | Trait | Primary Data | Secondary Data |
| Perca fluviatilis | Female | Onset of oogenesis | August and then increase proceeds regulalry through the winter and spring till the spawing time in May | ['January', 'February', 'March', 'April', 'May', 'June', 'August'] |
| Perca fluviatilis | Female | Maximum GSI value | About 20% [Prior to spawning, in May] | 20.0 percent |
| Perca fluviatilis | Female | Resting period | Mid-summer | 4.0 months |
| Perca fluviatilis | Male | Onset of spermatogenesis | August | ['August'] |
| Perca fluviatilis | Male | Main spermatogenesis activity | September-October, then remain at this size during winter until spring | ['January', 'February', 'March', 'April', 'May', 'June', 'September', 'October'] |
| Perca fluviatilis | Male | Maximum GSI value | About 8% [October] | 8.0 percent |
| Perca fluviatilis | Male | Spermatogenesis duration | About 6 weeks | 6.0 months |
| Perca fluviatilis | Male | Resting period | < 1% [June, July, and most of August] | 1.0 months |