The effects of an artificially prolonged photoperiod on growth, survival rate, colouration, and sexual maturation in brook trout Salvelinus fontinalis during pre-and post-spawning periods from 21 June to 06 November were investigated. Fish of mean initial weight~150 g were reared at ambient photoperiod as well as with an artificially prolonged photoperiod produced by either a light-emitting diode or a metal-halide light. The fish groups subjected to a prolonged period of artificial light grew significantly larger and had a higher survival rate (p < 0.05), regardless of sex, and showed lower occurrence of fungal disease compared to controls reared in the natural photoperiod. We found a significantly higher number of sexually mature fish in the control groups compared with experimental groups. The increased photoperiod effectively delayed gonad development and increased somatic growth in both male and female brook trout, and also increased resistance to fungal disease. The increased photoperiod produced an observable difference in fish colouration, with control groups exhibiting more intensive spawning colouration.

We evaluated the growth and survival rate of sterlet (Acipenser ruthenus) larvae fed Artemia nauplii enriched with Olioω3 or Red Pepper commercial emulsions (BernAqua NV, Belgium). Sterlet larvae, 0.022 ± 0.002 g body weight, were randomly assigned to one of three feeding regimes with two different feeding durations. After administering live feed for 7 or 14 days, larvae were weaned onto commercial food and reared to 36 days posthatching (28 days of feeding). There were no significant differences in body weight among groups at the end of the trial. A significantly higher survival rate (p < 0.05) was observed in larvae fed Artemia enriched with Red Pepper for 14 days compared to other feeding regimes. Based on the analysis of growth parameters, we can conclude that 7 days of live feeding to be sufficient for efficient rearing of sterlet larvae. And longer duration of live feeding with use of special enrichment can be recommended for a higher survival rate.

The influence of timing of extended photoperiods on growth and maturity of brook trout was investigated in a 112‐day experiment. The fish with mean initial weight of ~192 g were reared under four light regimes: one control group with natural ambient photoperiod and three groups exposed to an 18L:6D regime initiated at days 1, 23 or 46 of the growth trial. Light‐emitting diodes, with intensity of 250–1000 lux, depending on the distance from the light source, were used for extending light periods. There was a positive effect of prolonged day length on fish growth (p < 0.05), and a delay in gonad development and sexual maturity. Significantly higher numbers of sexually mature fish were found among controls groups, regardless of sex. Survival rate was not affected by light regime. This study demonstrated that the short‐term expansion of the photo period delayed maturation and increased the growth rate of brook trout.

No abstract

The artificial prolongation of daylight is generally used to delay sexual maturation in many cultured species, mainly in salmonids. This may have a negative impact on flesh quality. Therefore, we aimed to investigate the impact of photostimulation on post‐mortem changes; sensory, textural and nutritional characteristics of flesh of brook trout, Salvelinus fontinalis. Farmed brook trout were randomly divided into four experimental groups, according to photoperiod and sex for 112 days. Fish body traits and flesh quality of experimental fish were examined by body weight (g), gonadosomatic, hepatosomatic and perivisceral fat indices (%), rigor index (%), pH changes, fillet contraction (%), gaping, flesh water losses, textural, colour and sensory analyses and finally fat content and fatty acid (FA) composition. The results of pH measurement and rigor mortis showed that lower values of pH were measured in fish under artificial photoperiod (AP) during the entire measurement with faster progress of rigor mortis in comparison to fish under natural photoperiod (NP, control). In colour measurement, significant differences were detected in lightness L*, where NP fish (mature) were lighter than AP fish (immature). Significantly higher fillet contraction (p < 0.05) more than 7% were observed among AP females compared to the control groups. Finally, we documented that extension of light period has a positive effect on the sensory evaluation, the fat content and FA composition of brook trout flesh, but the effect is only minimal.