The delivery system was comprised of four components: 1) main dispenser body, 2) air delivery system, 3) sight glass, and 4) tank bracket system. The main body of the dispenser was constructed from 152 mm diameter Standard Dimension Ratio 35 (SDR 35) Polyvinyl Chloride (PVC) sewer pipe cut to 413 mm long. A 152 mm SDR 35 PVC cap was glued onto the 413 mm pipe using clear PVC Primer and Regular Body Medium Set PVC glue (Figure 1). The union of the cap and cut length of pipe produced a capacity of 5.5 liters with 108 mm of free board to prevent spilling.

A 15.9 mm hole was drilled into the top of the dispenser to install fittings for the internal air delivery system. From inside the dispenser, the threaded end of a 9.5 mm-barbed × 9.5 mm-male pipe thread (MPT) polyethylene 90-degree elbow was inserted through the hole. Inside the dispenser, a 330 mm length of 9.5 mm inner diameter (I.D.) clear vinyl tubing connected the barbed end of the MPT elbow to a 52 mm aquarium air stone (Figure 2).

Figure 2. The inner air delivery system for a novel Artemia feeder.

On the outside, a 9.5 mm barbed × 9.5 mm -female pipe thread (FPT) polyethylene 90-degree elbow was threaded onto the exposed male pipe threads to secure the connection (Figure 3). A 9.5 mm I.D. clear vinyl tubing connected the barbed end of the FPT elbow to a common airline supplying all Artemia dispensers. A constant air supply provided oxygen and ensured a homogenous concentration of Artemia throughout the feeding cycle. The common airline was made from 12.7 mm clear vinyl tubing (Sioux Chief, Kansas City, Missouri, USA) and branched to each Artemia dispenser using 12.7 mm × 12.7 mm × 9.5 mm barbed tees (Figure 4). Air was supplied to the common airline by an Aqua Miracle AP160 diaphragm air pump (Amazon, Seattle, Washington, USA).

A 12 mm hole was drilled in the center of the glued cap at the bottom of the feeder, and an 8 mm Uniseal (The Uniseal Warehouse, St. Cloud, Florida, USA) was inserted into the hole. A 100 mm length of 9.5 mm outside diameter (O.D.) PEX tubing was then pushed through the Uniseal (Figure 5). A 9.5 mm push-to-connect plastic valve (Watts AquaLock Push-to-Connect Plastic Valve, Watts Water Technologies, North Andover, Massachusetts, USA) was attached to the protruding end of the PEX tubing. This valve, positioned at the lowest point of the dispenser, allowed for modulation of the Artemia slurry dispersion rate.

At the bottom (cap end) of the feeder a 14.7 mm hole was drilled approximately 25 mm from the base of the dispenser. Threads were cut into the drilled hole using a 9.525 mm, 18 NPT tap, and a 9.5 mm barbed × 9.5 mm MPT 90-degree elbow was threaded into the tapped hole. A 380 mm section of 9.5 mm I.D. tubing was affixed to the barbed end of the MPT elbow and oriented to the top of the dispenser. Near the top of the dispenser, two 4.8 mm holes were drilled 19 mm from the rim, and a cable tie was used to secure open end of the tubing. Marks were added to the tubing in 0.5 liter increments, from 1.0 liter to 5.5 liters, to reflect the volume of Artemia slurry within the dispenser (Figure 6).

To position the Artemia dispenser above the fish culture units, a stainless-steel Arvo-Tec TD 2000 Hinged Hanger was used (Arvo-Tec Oy, Huutokoski, Finland). The hanger has two bands originally designed to secure the top of an Arvo-Tec TD 2000 feeder. These two bands closely matched the diameter of the Artemia dispenser and were easily adapted to fit with a tension hold when bolted together (Figure 7). To mount the hanger to the tank wall, a piece of 4.8 mm × 51 mm aluminum angle, approximately 140 mm in length, was attached to the bottom of the hanger using two M6 × 1.0 mm × 25 mm stainless steel bolts, lock washers, and hex nuts. This modification allowed the dispenser to be easily mounted to the tank wall by sliding it over the tank lip (Figure 8).

The cost to construct the entire feeder was approximately $20 USD. In contrast, the cost of commercially available Artemia dispensers for aquaculture use range from $300 to over $1,500 USD.

The first retrofit replaced the push-lock fitting with a series of vinyl tubing segments, each progressively reducing in diameter to decrease the flow rate (Figure 9). The protruding PEX tubing fit securely into 9.5 mm I.D. clear vinyl tubing, followed by a series of step-down connections: 6.4 mm I.D., 4.8 mm I.D., and a 2.38 mm fuel line. At each transition, the outer diameter of the smaller tubing allowed for a secure, press-fit connection into the inner diameter of the next larger segment. This retrofit improved reliability, but accuracy was still problematic.

The second retrofit retained the 9.5 mm, 6.4 mm, and 4.8 mm I.D. segments of tubing, but added a dripline irrigation valve (Rain Bird, Azusa, California, USA) onto the 4.8 mm I.D. segment (Figure 10). The addition of the drip line valve improved accuracy and reliability to an acceptable level. To standardize starting volumes, each dispenser was filled with the correct Artemia concentration and a 30 ppt salt buffer added to the 5.5 liter mark of each feeder. A standard starting point in each dispenser allowed hatchery staff to monitor and adjust dosing rates throughout the day. Adding this salt buffer prior to adding Artemia also decreased slurry viscosity, which greatly improved Artemia dispensing by the feeder.

During actual operation, the feeders produced mixed results. It was critical to thoroughly remove unhatched cysts and eggshells to prevent clogging in the narrow diameter drip lines. Under ideal conditions, feeders extended feeding events by three hours, short of the six-hour goal. This resulted in more frequent-than-desired refills to maintain target Artemia stocking densities.