Introduction
Pikeperch (Sander lucioperca (L., 1758)) is a promising candidate for the diversification of inland aquaculture in Europe, although the production of sufficient fingerlings remains a bottleneck. The most critical stage of life during fish production is the larval period. Numerous factors regulate the larval survival, including environmental parameters (e.g. water quality, water temperature, and photoperiod), nutritional – (e.g. feeding frequency, weaning strategy), and population factors (e.g. stocking density).
The microbial environment of fish larvae is an additional factor that may determine the production success, since the microbes interact with the larvae at different levels. Microbes with an external origin (water and feed) will colonise the digestive tract of the fish and therefore influence the health status of the animal. The microbial community from the intestine of teleosts, namely fish gut microbiome, is an important element, ensuring the proper growth and health. However, in order to ensure economic production, the animals are confronted with various challenges. These include switching from live feed to commercial dry feed, called the weaning process. The microbiome changes abruptly with the habituation to dry feed. The status of the environmental and gut microbiome during this process under different feeding regimes and environmental conditions is still not evident in pikeperch. Information about microbial communities could provide key aspects related to the fish larvae production.
We aimed to assess the effect of water temperature on fish performance and the microbial communities of the system, and to describe the microbial communities present in the water, the fish gut, and the feed during the initial stages of larval rearing, after first feeding.
Material and methods
In a 47-day larval rearing experiment, we investigated the differences between two temperature regimes (16 °C vs. 20 °C) in two identical recirculated systems. The 500-litre tanks were used in triplicate, combined with high stocking densities (150 larvae/litre), and a 24-hour photoperiod. For the microbiological investigation, samples of water and fish larvae were collected in triplicates at three time points (24, 34 and 47 days post-hatch: T1, T2, and T3). After DNA extraction, we sent the samples to Edinburgh Genetics Limited for whole genome sequencing and metagenomic sequencing analysis. Data and statistical analysis were conducted using various diversity indices, PCoA, Bray-Curtis ANOSIM, and relative abundances of taxa. To assess larval performance, we measured growth parameters (body wet-weight, total length), survival rate, swim bladder inflation rate, and the occurrence of jaw and spine deformities. Statistical differences were evaluated (p < 0.05) using one-way ANOVA and Mann-Whitney U Test (SPSS 29.0, IBM Co., Armonk, NY, USA).
Results and conclusion
At 20 °C, the larvae performed significantly better in terms of final wet-weight, final total length, and swimbladder inflation rate compared to the 16 °C system. However, we found no significant differences regarding the survival and deformation rates.
We observed a temporal variation in water microbial community structure and composition. Regarding the two different temperatures (16 °C vs. 20 °C), no statistically significant differences were detected in either the water microbial community or the fish microbiome. In the rearing water, Vibrio sp. and Pseudoalteromonas sp. were the dominant pathogens at T1, but their abundance decreased at T2 and T3. At T2 and T3, the dominant pathogen was Aeromonas sp.
In conclusion, higher rearing temperatures can enhance the growth and performance of pikeperch larvae without significant negative effects. Further investigations are required to address the non-significant, yet visible differences at 20 °C, such as higher deformity rates and a relatively higher abundance of Vibrio sp. in the larvae gut during the live feed period.
The European Fisheries Fund (EMFAF) and the Ministry of Agriculture and Environment from Mecklenburg-Western Pomerania funded this study as part of the project Fish pathogens from fish farms and waters of the Northeast German Lake District (project number MV-II. 12-LM-03).