In the cultivation of different marine fish larvae, several protocols have been developed to tackle existing bottlenecks . This resulted in a stable production for species such as sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata ). However, existing protocols are species-specific and for other fish can only be used to a limited extent, especially for freshwater fish species, such as pikeperch (Sander lucioperca). Intensive pikeperch larviculture presents a challenging task that requires fine-tuned rearing conditions to reach a reasonable outcome. Low survival rates can be caused by improper swimbladder inflation, deformities, and especially cannibalism. To improve the production efficiency in larval fish culture , it is crucial to consider multitude of biotic and abiotic factors and their interactions.
Beside the effect of the “greenwater” technique compared to standard clear water protocols, two different photo regimes (12/L:12/D vs 24/L:0/D) were examined in two identical recirculated systems. Simultaneously , we compared the influence of stocking density levels (50 larvae/L vs 150 larvae/L) , while a fourth factor was a post-weaning feed , considering the reduction of production costs (Expensive vs Low price). The trial was conducted in a full design (model: 2^4; 16 combinations. During 47 days, multiple variables were followed: growth parameters - body weight (g) and length (mm) and their coefficients of variations, condition factor and specific growth rate . In addition, the occurrence of jaw and spine deformities, survival and swim bladd er inflation rate 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) was applied, to compare the strength of factors . (XLSTAT, Long Island: New York, NY, USA, 2023).
Our findings revealed that a shorter photoperiod had significant (p < 0.05) positive effect on swim bladder inflation . Furthermore, a prolonged light period under greenwater conditions improved homogeneity in growth of each cohort , which was shown by lower coefficient of variation . In larvae reared under greenwater conditions, significant higher survival rate (p < 0.05) was detected. These results indicate that a supply of algae during the cultivation of pikeperch larvae could improve the rearing success. To reach a reliable production f urther investigations are required to determine the most efficient conditions with all crucial parameters e.g. a practical photo regime and compare the best combinations in different rearing systems.