Introduction
Intensive pikeperch larviculture presents a challenging task and is still the limiting factor for the expansion of successful production. In addition to a high level of cannibalism, which causes high mortality rates, this is primarily due to the quality of the fingerlings produced. The loss of quality is significantly reflected in the deformation rate, which in turn increases cannibalistic behavior. In pikeperch, it is known that this phenomenon mainly occurs between days 19 and 39 post-hatch, depending on the rearing temperature, which is a rather long period from a production point of view. In addition to an existing dark period, cannibalism is also promoted by the habituation to commercial dry feed, as the nutrient composition changes drastically and the prey stimulus changes due to a lack of agility. However, the drastic change in the nutrient composition, especially if no appropriate biosynthesis of enzymes has taken place, caused by live food reduction, can lead to nutritional deficiencies and consequently to deformities. Nevertheless, the rearing temperature is a success-determining factor in addition to those already mentioned being decisive for the rate and quality of metabolism, but can also detriment development. Overall, it is evident that all effects have common factors and interact among each other.
Material & Methods
Besides the effect of two different photo regimes (16/L:8/D vs 24/L:0/D), two different rearing temperatures (16 °C vs 19 °C) were examined in two identical recirculated systems. Simultaneously, we compared the influence of the dietary enrichment of Artemia (enriched vs non-enriched). The trial was conducted in a multi-factorial design and groups were duplicated (model: 2^3 ; 8 combinations; 16 tanks). During 47 days, multiple variables were followed : growth parameters - body weight (g) and length (mm) and their coefficients of variation, condition factor and specific growth rate. In addition, the occurrence of jaw and spine deformities, survival and swim bladder inflation dynamics were assessed . Main effects and interactions were analyzed with SPSS 29.0 (IBM Co., Armonk, NY, USA) in the General Linear Model, Univariate ANOVA. Afterwards, Principal Component Analysis and Pearson correlation (n-1) were applied to compare the strength of factors. (XLSTAT, Long Island: New York, NY, USA, 2023).
Results
Our findings revealed that a higher temperature had significant positive effect on the speed and efficacy of swim bladder inflation at day 12 (p = 0.003), day 23 (p = 0.002), and 47 (p < 0.001) post hatch, as well as on the total length (p < 0.001) and wet weight (p < 0.01) on day 47 post hatch. Furthermore, a higher rearing temperature improved homogeneity in growth, visible by a lower coefficient of variation (CV wet weight: p = 0.014). Considering photoperiod, it became apparent that it positively influenced growth shown in a higher wet weight (p = 0.037) at final sampling time. The third factor investigated, the enrichment of the Artemia , had a significant effect on the survival rate (p = 0.005). These results indicate that rearing pikeperch larvae at a relatively higher temperature of 19 ºC could improve the rearing success , while the enrichment of Artemia nauplii seems necessary. To reach a stable juvenile production, further investigations are required to determine the most efficient conditions with all crucial parameters e.g. a practical photo regime, algae product and its application rate (i.e. turbidity level), as well as applying older stages of Artemia (i.e. Instar II) aiming for reliable, efficient and universally applicable protocol.