Effect of photoperiod on ovarian maturation in Cheirodon interruptus (Teleostei: Characidae)

Cheirodon interruptus is a ubiquitous small characid that inhabits the Pampean region and commonly used as bait. Its vast market is supplied from the wild population causing a significant environmental impact. In this study, we assess the effect of photoperiod on ovarian maturation in order to evaluate its potential as a tool to manipulate reproduction under artificial conditions. Four treatments in triplicate (light: dark, L: D) were tested: 24L: 0D, 12L: 12D, 0L: 24D and a progressive photoperiod corresponding to the daily photoperiod increments in wild during winter-spring transition, accelerated three times. The experiment was conducted for 45 days. Gonadosomatic index (GSI), oocyte mean diameter, vitellogenic oocyte proportions, plasma estradiol concentrations (E2), condition factor (Kn) and standard length were estimated. Values of mean GSI, oocyte diameter, vitellogenic oocyte proportions and E2 concentration were maximum in the progressive treatment indicating vitellogenesis stimulation. In turn the same parameters were minimum in the 24L: 0D, revealing the vitellogenesis inhibition. This study showed that photoperiodic regime play an important role in the onset of ovarian maturation in C. interruptus.

Effects of ration on the maturation and fecundity in captive Atlantic herring (Clupea harengus)

We examined the effects of amount of food on vitellogenic oocyte size and number (fecundity) between two experimental groups of Atlantic herring (Clupea harengus) kept in separate but identical compartments of a large seawater tank. Growth and maturation were monitored for 1.5 years. Each group of 200 fish was fed exclusively on krill. At the end of the experiment, a high-ration group, fed 12 mg ·g fish-1 ·day-1, had similar weights-at-length as wild specimens of the same stock. A low-ration group fed about half the amount of the high-ration group had significantly lower weights-at-length. Ration had no effect on oocyte size and relative potential fecundity (oocytes per gram), but mean potential fecundity (oocytes per fish) of the low-ration fish was 26% lower than that of the high-ration fish. The relative intensity of early stages of atresia was quantified histologically. Atresia is a common phenomenon in Atlantic herring and increases markedly with suboptimal feeding. Mean relative atretic intensities were estimated at about 3 and 6% for the high- and low-ration groups, respectively, but with large intragroup variation. Modeled realized fecundity (spawned eggs per fish) indicated a 9 and 40% reduction compared with the measured potential fecundities, respectively.