# Rearing Conditions and Automated Feed Distribution Systems for Zebrafish (_Danio rerio_)
## 3 Designed Culture Systems  
The development of common husbandry schemes for zebrafish has improved together with the use of this fish in laboratories to ensure not only that next fish generations are produced but also that vigor and robustness of the strains are preserved. Yet, basic standard protocols for zebrafish rearing in laboratory conditions are still designed to improve fast growth and high reproduction rates rather than to address adequate nutrient requirements and overall fish health and welfare (2018). To standardize zebrafish rearing procedures, many different culture systems have been developed based on the specific needs of laboratories or institutions. Generally, these systems are referred as (a) flow-through, (b) recirculating, or (c) static renewal (2018, 2019; 2020). The flow-through system is the least common design among research laboratories, although it offers several advantages when performing nutritional experiments. The principle involves large volumes of water (filtered or unfiltered) that are quickly pumped in the facility tanks and thereafter returned to the environment, usually after remediation, with no appreciable amounts of waste materials and, whether accumulated, removal does not need great effort. Once established, the system does not require expensive costs to operate. Furthermore, it also represents the best approach to minimize the build-up of nitrogenous wastes in zebrafish tanks. However, the tank water quality depends mostly on the source and, thus, it follows a high probability of including pollutants or toxicological elements, which can negatively affect zebrafish wellness and growth. Flow-through systems have \begin{table}
\begin{tabular}{c c} \hline \hline
**Specific Parameter** & **Recommendations** \\ \hline Temperature & Adult zebrafish exhibit tolerance for a wide range of water temperatures (24.0–29.0 \({}^{\circ}\)C). For zebrafish embryos and larvae, the recommended \\  & rearing temperature is 28.5 \({}^{\circ}\)C. Lower temperatures may slow down \\  & the development. \\ \hline pH & For both larval and adult zebrafish, a pH range from 6.5 to 8.0 \\  & is recommended. \\ \hline Light/dark cycle & Fourteen hours day (light) and 10 h night (dark) is generally \\  & recommended for both adult and larval zebrafish. The light/dark cycle \\  & does not seem to affect zebrafish embryonic development. \\ \hline Salinity (total concentration of ions dissolved in water) & A range 0.25–0.75 part per thousand (ppt) is recommended for adult and \\  & larval zebrafish. \\ \hline Conductivity (the quantity of sodium and chloride or  calcium and carbonate) & In recirculating water systems, a 150–1700 \(\upmu\)S/cm range is recommended. \\ \hline Oxygen and NH\({}_{3}\) & In recirculating water systems, dissolved oxygen levels are kept at \\  & approx. 7.8 mg/L at 28.0 \({}^{\circ}\)C. Levels of total ammonia, nitrites, and \\  & nitrates are generally kept less than 0.1, 0.3, and 25 mg/L, respectively. \\ \hline Hardness (concentration of divalent ions, such as Ca2\({}^{+}\) and Mg2\({}^{+}\), and carbonate, such as CaCO\({}_{3}\) and MgCO\({}_{3}\)) & A range between 75 and 200 mg/L (generally above 100 mg/L) is \\  & generally recommended. \\ \hline Density & Adult sexually mature zebrafish are recommended to be maintained in a \\  & range between 3 and 12 fish/L. Zebrafish embryos are cultured in 9 cm \\  & Petri dishes at a stock density of up to 100 embryos/35 mL. Larval zebrafish from 6 to 16 days post-fertilization (dpf) are recommended to be \\  & raised in small tanks with no water flow at a density up to 60 larvae/L. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters and recommendations for zebrafish rearing. been used for maintaining zebrafish in the laboratory by [PERSON] [35] and [PERSON] et al. [36], for example. The basic concept of flow-through system has been used for the development of microfluidic systems for culturing of zebrafish embryos and larvae.