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4.3 Fingerling Production and Supply
Fingerlings for fish culture can either be obtained from a supplier or produced in-house. Availability, price, number of fingerlings needed, and level of expertise are the main factors that determine the method of choice. Type of species cultured, season, and location can also heavily influence the methods. Supply: The best option for small-scale producers is to buy from a supplier. Suppliers should maintain detailed breeding records, use high-quality broodstock, and implement Best Aquaculture Practices (BAPs).
· Kentucky State University4.2 Species Overviews
Tilapia: Tilapia (usually Oreochromis niloticus or the Nile tilapia) are the most cultured fish in aquaponic systems. They are tolerant of both crowding and relatively poor water quality conditions. They do best at water temperatures of 25-30°C. At temperatures < 24°C, their growth slows substantially, and they become susceptible to disease. They breed readily and abundantly. In fact, if using mixed sex fish, unintended spawning in the system can be a problem particularly in DWC beds where tilapia will consume all available plant roots.
· Kentucky State University4.1 Suitable Species of Fish for Culture
Unfortunately, not all fish species adapt well to tank culture, just as not all animal species adapt to being farm animals. Since fish are cold blooded, almost everything about their growth and health is influenced by temperature (see Tables 4 and 6 for details). The temperature of the culture water will partially dictate what species can or should be raised in your system. Other important factors will be how densely you intend to raise them and for what purpose or market.
· Kentucky State University3.2 Disposal of Waste
Recovery and digestion of fish effluent is more important in aquaponics than waste disposal. A large portion of feed is excreted as solid waste. Nutrients essential for plant growth are trapped within this concentrated slurry and should be recovered to reduce production costs and limit the need for nutrient supplementation. Recovery of these nutrients moves aquaponic production towards a zero-discharge system. Nutrients can be recovered through aerobic or anaerobic digestion of solids.
· Kentucky State University3.1 Water Sources
Sourcing water is an important consideration, as it directly impacts system management and performance. Typically, 1-3% of total system water is replaced per day depending on climate, time of year, and crops being produced (Somerville et al. 2014). Water is lost in the system through evaporation, transpiration into the plant, and through normal processes of splashing, cleaning, and harvesting. Water with a salinity above 0.8 parts per thousand (ppt) are typically not suitable for aquaponic production as the majority of cultured plants do not tolerate even a small degree of salt (Shannon and Grieve 1998).
· Kentucky State University2.5 Sump
The sump is the lowest point of the system and where water collects to be distributed as needed throughout the system. Water quality samples can be taken here and amendments can be made without overwhelming the fish or hydroponic components. While not a requirement, the addition of a sump prevents the water level from changing in either the fish tank or hydroponic component. In other cases where safeguards are put in place, the fish tank or hydroponic component can be used as the sump.
· Kentucky State University2.4 Plant Culture or Hydroponic Subsystem
The hydroponic portion of the system encompasses the majority of the facility footprint. Three primary designs are used: media beds, deep water culture (DWC), and NFT. Media-based systems: The design of media-based systems, sometimes called flood-and- drain, is fairly straight forward. A container filled with substrate is periodically flooded with water from the fish tank. Water then drains back to the sump (or fish tank) drawing oxygen into the substrate for plant roots and nitrifying bacteria.
· Kentucky State University2.3 Biological Filtration
Biological filtration refers to the breakdown of ammonia (NH~3~ and NH~4~+) into nitrite (NO~2~) and then further into nitrate (NO~3~) by naturally occurring, nitrifying bacteria. These bacteria live on the surface area of media contained in a tank collectively called the biofilter. The process of converting ammonia to nitrate will be detailed in the section on water quality. In RAS, the biofilter is designed to operate at low pressure. There is a dedicated tank filled with substrate like Kaldnes media, granular media, plastic balls, or other inert materials that have a large specific surface area or surface area of the media per unit volume.
· Kentucky State University2.2 Solids Filtration
Effective solids filtration is a key component to a well-functioning system and potentially the most important aspect as it influences the efficiency of all other processes. Solids are mostly produced from uneaten feed, fish waste, and bacteria biofilms (classified as suspended solids) (Timmons and Ebeling 2013). If waste is not removed, it can settle on plant roots (preventing uptake of nutrients), collect in areas of low water flow (resulting in poor water quality), cause the build-up of noxious gas, and clog pipes (preventing sufficient water flow) (Somerville et al.
· Kentucky State University2.1 Fish Culture
Fish tanks for aquaponics come in a wide range of shapes, sizes, and materials, with selection being largely based on culture species. The majority of large systems use round tanks that either have a flat- or cone-bottom. Use of tangential flow will prevent dead zones when used in round tanks (Figure 2). Cone-bottom tanks allow solids to concentrate at the bottom (in the cone) and be easily flushed from the system.
· Kentucky State University