Aquaculture production is predicted to increase sharply. In this regard, live feed plays a crucial role in the larval phase of many aquaculture organisms. Hence, a persistent concern in aquaculture is to find low‐cost and eco‐friendly feed sources to culture live feed organisms. Branchinecta orientalis (G. O. Sars 1901), a fresh/brackish water fairy shrimp, was reared using effluent from rainbow trout Oncorhynchus mykiss (Walbaum 1792) ponds, either fresh but supplemented with two species of microalgae, Scenedesmus sp. and Haematococcus sp., or non‐supplemented but after “ageing” of the culture medium. The feeding experiment was designed at a density of 100 individuals L−1 in 2‐L vessels. The results indicated that differences between final length, survival and most reproductive parameters of the treatment with aged medium and the treatment using fresh medium supplemented with Scenedesmus sp. were non‐significant (p > .05). Better results were obtained for a number of reproductive parameters in the treatment supplemented with Haematococcus sp. Thus, for intensive resting egg production of B. orientalis, microalgae can be replaced by aged non‐supplemented effluent from trout ponds as a nutrient‐rich feed source. This consequently can reduce drainage of nutrients into the environment and thus decrease aquatic pollution.

Highly variable environmental conditions can put the survival of inhabitants of temporary pools at high risk, as they may not complete their life cycle. Different evolutionary responses can prevent the extinction of the inhabitants of ephemeral wetland habitats. One specific mode of response to environmental changes is bet-hedging as risk-spreading strategy and long-term fluctuating selection. The fairy shrimp Branchinecta orientalis G.O. Sars, 1901 is a broadly distributed species in Europe and Asia. We investigated the hatching pattern of B. orientalis resting eggs as a result of various factors, alone or interacting: 1) brood order, 2) food supplied to the parental generation, and 3) various pre-inundation conditions. Results were recorded for cumulative hatching over 10 d, hatching at the first day, and the first day of hatching. The factors with significant effects on hatching percentage were 1) brood order, 2) type of food, 3) pre-inundation conditions, 4) interaction between brood order and type of food, and 5) interaction between type of food and pre-inundation conditions (P < 0.05). Within the first 24 h, 44% of total hatching occurred. Resting eggs from the first brood showed the highest cumulative hatching. The lowest mean resting egg size was found when parents were fed fish pond effluents supplemented with Haematococcus sp. (Chlorophyta); this group of resting eggs also had the highest cumulative hatching percentage. Eggs that had stayed for one week in the parental medium showed significantly higher cumulative hatching percentage, than eggs that had stayed in the medium for two weeks, or that had not stayed in the medium at all (P < 0.05). Overall, hatching showed an irregular pattern, affected by the mode of response of the resting eggs to our experimental factors. The irregular hatching pattern may result in fairy shrimps better adapted to environmental instability.

Very little is known about the feeding of naupliar and juvenile life stages of omnivorous fairy shrimps (Crustacea: Anostraca). Here, we aim to reveal whether the fairy shrimp Branchinecta orientalis is an ontogenetic omnivore and at which age and ontogenetic stage they gain the ability to feed on zooplankton. We assess how food uptake rates change with age until reaching maturity by providing algae (pico- and nanoplanktonic unicellular algae) and zooplankton (rotifers and copepod nauplii) as food in individual experiments. We found that the fairy shrimp B. orientalis started to feed on both types of algal prey immediately after hatching. Nanoplanktonic algae likely represented the most important food source until reaching maturity. Moreover, fairy shrimps started to feed on zooplankton already when they were 7 days old. Slow-moving rotifers gradually gained importance in the fairy shrimp diet with time. Our results reveal an ontogenetic change in the prey spectrum of fairy shrimp. The systematic shift towards omnivory likely affects both phyto- and zooplankton community composition, possibly contributing to temporal changes in food web dynamics in fairy shrimp habitats, and temporary ponds, which may warrant more detailed investigations in future studies.