Depending on the bait they're designed to hold, portable livewells can run the gamut from simple D-cell-operated bubblers clamped to the side of a five-gallon bucket to bottled oxygen with specialty air stones on 100-gallon molded plastic containers. While the latter is the extreme, the configuration of your portable livewell should be based on the needs of the bait you intend to carry.
Water volume, oxygen content and the bait's own waste products are all considerations when choosing a portable livewell, yet by taking the definition of the term "portable" to mean "as lightweight and simple as possible," it's best not to overthink your livewell needs. The variety of different portable aeration systems and their effectiveness at delivering oxygen into a closed system are the defining essentials for arriving at your destination with the sturdiest baits possible.
Baits Have Needs
Depending on the bait species you carry, the volume of dissolved oxygen in your livewell may not be a huge factor. For instance, with shrimp and crabs, a simple battery-operated bubbler works fine, even if you plan to keep your bait alive for extended periods. In this case, water level is a major consideration since volume creates pressure and disperses the oxygen throughout the water column as the bubbles from the air stone rise to the surface. Yet the majority of these baits lie on the bottom. For maximum efficiency, keep the water level in your livewell at only three or four inches, which will help saturate the water with oxygen where the crustaceans are holding.
Baitfish are a different case: You need to consider the delicacy of the species and the number of baits in your livewell. Simple bubble systems are inefficient at putting enough oxygen into the system because the large bubbles produced by the standard air stone release minimal amounts of oxygen into the water. A commercial air stone, typically a 3-inch ring, diffuses the oxygen through smaller holes, creating more surface area and pushing more oxygen into the water.
Closed systems like this might be great for cocahoe minnows (killifish), pinfish and mullet, but constantly swimming baitfish like shad, herring and sardines need water flow in the livewell to move oxygen across their gills.
Go with the Flow
Spray jets are the most common method of adding flow (and often improving oxygen delivery) to a livewell. These systems drive large volumes of water through a spray head via a 12-volt pump, creating flow and pulling oxygen into the water.
This system offers a better choice for keeping baitfish lively.