# Rearing Conditions and Automated Feed Distribution Systems for Zebrafish (_Danio rerio_)
## 4 Feeding Requirements
### Formulated Diets  
Currently, several different formulated diets are available for zebrafish, including commercial dry feeds and live feed such as _Artenia_ nauplii, rotifers (_Brachionus_ sp. ), _Paramecium caudatum_, and _Tetralyprena_. Among these, dry diets are generally assumed to be nutritionally complete, whereas live feed stimulates the associated predatory (fish-prey capture) behavior [30; 58; 59]. Zebrafish dry diets can be classified based on ingredient and nutrient composition: while some diets are used for specific nutrient requirements under determined experimental conditions, others have commercial applications and are designed for large-scale production [31]. \begin{table}
\begin{tabular}{c c} \hline
**Microfluidic System** & **Description** \\ \hline [PERSON] et al. [37] & A chip for a one-step automatic loading, hydrodynamic positioning, trapping, and long-term immobilization of single embryos. \\ \hline [PERSON] et al. [45] & A device with branching channels for manual loading, positioning, and orientation of 3-5 dpf zebrafish larvae, allowing both dorsal and lateral view of the fish. \\ \hline [PERSON] et al. [46; 47] & A device consisting of two side-by-side horizontal channels bridged by a series of short, tapered channels and of a hydrodynamic force continuously applied. This force allows the loading and the immobilization of larvae which, once entrapped, can act as a plug directing the following larvae towards the empty channels in a sequential manner. \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._At the time of the complete development of the gut (at approx. 5 days post-fertilization, dpf) [60, 61], _Paremecium_, rotifers, and _Artemia_ nauplii are usually administered as first feed because they are useful for increasing survival and early growth, as indicated by various authors [31, 62]. Early zebrafish larvae prefer to consume _Pranecium_ and rotifers due to their small diameter, but not _Artemia_[29]. In this respect, [PERSON] et al. [63] showed the effective use of a static rotifer-larvae \"polyculture\" methods for feeding 5-9 dpf zebrafish. Naturally, since live food is a common vector of pathogens, care must be taken to minimize their spread. After a period of early development (which generally spans from a few days to several weeks), artificial feeds are introduced in zebrafish larval diet [31]. The administered commercial feeds can be used in two different ways, which are as supplement to live diets or as the sole food source [27]. Currently, the most standard and widespread protocols for zebrafish nutrition include the administration of live feed combined with processed feed (usually as fish flake) or specific diets containing fish oil and fish meal, which have been shown to be sub-optimal in many ways [64, 65]. While live food such as _Artemia_ nauplii does not negatively affect fish growth and health (especially non-hatching decapsulated _Artemia_ cysts) in juvenile and adult zebrafish [66], the administration of rotifers and _Paramecium_ as live food shows large variability in nutritional profiles [67, 68], as well as the risk of spreading pathogens [69] and toxic compounds, which may negatively affect fish health status [70]. For these reasons, live food as the sole source of nutrients is not recommended, and a combination with artificial diets containing the remaining nutrients is preferred. As for live food, the use of flake feeds for juvenile and adult zebrafish is problematic as well, since determining the precise ingredients and the nutritional profile is difficult. Likewise, their poor stability in water means soluble nutrients leach into the water rather than being ingested by the fish [71]. Furthermore, formulated diets may contain potentially harmful compounds such as genistein and soy isoflavone, which have been shown to be an estrogen mimic in both fish and mammals [72, 73].