The effect of live feed diets containing Brachionus plicatilis (B) and Apocyclops panamensis (A) was investigated on pikeperch larval survival, growth, and fatty acid composition in two experiments (E1 and E2). Up to six different diets were provided to the larvae, in which the letters of the diet names represent the live feed organisms as mentioned above and the subsequent number of feed organisms per larva and day. In E1, start cultures with 35 larvae/L were supplied with two diets (B200 and B100 + A100) 7 days until 10 days post hatch (dph). In E2, 50 larvae/L were fed six diets, B280 + A120, B340 + A60, B400, B420 + A180, B510 + A90, and B600. The highest survival and specific growth rates (SGR) occurred in B200 (E1). In E2, B340 + A60 performed best. A trend of increasing survival rates was found in E1 from 68.9% (B100 + A100) to 71.6% B200 and in E2 from 64.0% (B280 + A120) to 93.7% (B340 + A60). Larval SGR tended to increase with higher shares of dietary B. plicatilis in both experiments. The polyunsaturated fatty acid, linoleic acid (LA), followed the same pattern as survival and SGR increasing until a plateau was reached, indirectly indicating a feeding threshold. B. plicatilis provided the LA to pikeperch larvae, which seemed to play an important role in this feeding period. Consequently, a live feed diet should contain at least 340 B. plicatilis ind. larva⁻¹ day⁻¹ and 6.3 B. plicatilis per milliliter until 10 dph to improve pikeperch larviculture.

A new cultivation system with the chlorophyte Monoraphidium contortum combined with a self-sustaining culture of the freshwater rotifer Brachionus calyciflorus was applied for Sander lucioperca (L.) larviculture. Survival, morphometrics, as well as fatty acid composition of pikeperch larvae were analyzed after a ten-day feeding period. By using the pseudo-green water technique with improved aeration and water movement at the surface, survival rates reached up to 94%, with a total larval length of 8.1 ± 0.3 mm and a specific length growth rate of up to 4.1% day⁻¹ for S. lucioperca. The biochemical composition of B. calyciflorus and especially its contents in C18 PUFAs and suitable n-3/n-6 ratios met the nutritional requirements of pikeperch larvae. The high abundance of highly unsaturated fatty acids (HUFAs) in the diet appeared to be less important in the first feeding due to a possible retention of essential fatty acids, which originate from the yolk sac reserves, at adequate levels. Exponential growth of microalgae and zooplankton under the applied conditions was most effective when stocking M. contortum five days and B. calyciflorus three days before adding the fish larvae. Appropriate timing and sufficient live feed density allowed a successful integration of B. calyciflorus into pikeperch larviculture. We hypothesize that feeding pikeperch larvae with a self-sustaining Brachionus-culture under pseudo-green water conditions with minor disruptions during larviculture will improve survival and growth. This system is a first step towards pikeperch larviculture inside recirculated aquaculture systems (RAS) under continuous feed supply with live feed within the same aquaculture unit.

The aquaculture production of pikeperch has reached commercial scale in a number of European countries, but the high mortality of early life cycle stages and minor understanding of nutritional requirements are still major bottlenecks. To investigate the fate of fatty acids during early development, weaning and rearing, pikeperch larvae and juveniles from a commercial recirculating aquaculture system (RAS) were sampled over 2 months for morphometric data, as well as fatty acid composition, with a total of 6 sampling days, with four to five replicates per sampling day and between 1 and 25 pikeperch larvae per individual sample, depending on larval biomass. The biomass of sampled pikeperch larvae varied from 0.1 to 420 mg (dry mass DM), depending on the age of the larvae, and the initial length of the pikeperch larvae was about 4.5 mm. Our data confirm that, accompanied by an exponential increase in dry mass, total fatty acids (TFAs) in larval tissues increased with the beginning of exogenous feed uptake and were depleted between days 13 and 25 post hatch, most likely associated with the weaning and metamorphosis of the larvae. We conclude that all fatty acid classes may serve as metabolic fuel during metamorphosis, but the ultimate fatty acid composition is strongly impacted by the available feed. The chosen diet probably caused a lack of alpha-linolenic (18:3n-3; ALA) and docosahexaenoic acid (22:6n-3; DHA) during larval development and a shortage of vaccenic (18:1n-7), alpha-linolenic (18:3n-3; ALA) and arachidonic acid (20:4n-6; ARA) in juvenile pikeperch. This led to low DHA/EPA ratios 13 days post hatch, a high EPA/ARA ratio at days 41 and 56 post hatch and a fluctuating ratio of alpha-linolenic acid to linoleic acid (18:2n-6; LA). A temporary lack of essential fatty acids can cause dysfunctions and eventually mortalities in pikeperch larvae and juveniles. Despite high larval growth rates, the biochemical composition of the first fed Artemia and microdiets was most likely not sufficient and in need of improvement. We suggest that deficiencies must be compensated, e.g., through the substitution of the offered Artemia with more suitable live feed organisms, such as freshwater rotifers, and the enrichment of current microdiets in order to prevent high mortalities during pikeperch rearing and weaning.

Alternative live feeds for small and sensitive fish early life stages such as pikeperch (Sander lucioperca L., 1758) can improve the larval quantity, quality and performance in aquaculture. Therefore, this study evaluated the cyclopoid copepod Apocyclops panamensis (Marsh, 1913) as live feed for pikeperch larviculture from day 11 post hatch (dph) in two independent experiments. In both experiments, pikeperch larvae had the highest specific growth rate (SGR) when they fed on Brachionus plicatilis until dph 11 and A. panamensis until dph 16–18. SGR was related to a decrease in total fatty acids (FAs), saturated FAs and monounsaturated FAs in pikeperch larvae, indicating their use as energy for growth. Within the polyunsaturated FAs, docosahexaenoic acid (DHA) increased in larvae fed with A. panamensis and coincided with the highest SGR suggesting that DHA is accumulated in larvae as structural FA. Our study demonstrated a suitable pikeperch larval fatty acid composition for growth after feeding A. panamensis compared with Artemia sp. from dph 11 until dph 16 and previously fed with B. plicatilis. Moreover, it highlighted the importance of the dietary PUFAs in pikeperch rearing, specifically of linoleic acid (LA) from dph 4 until dph 11 and of DHA from dph 11 onwards.