Saab's Seaeye Falcon DR remotely operated vehicle (ROV) is used in a wide variety of applications, including oil & gas exploration, scientific exploration and data-gathering, and environmental monitoring. Its depth rating is 1,000 m (3,280 ft), and its maximum tether length is 1,100 m (3,608.9 ft) with a 14 mm (0.55 inch) diameter umbilical, although longer options can be achieved with custom umbilicals. It runs on a single-phase, universal auto-sensing, self-selecting input of 100-270V AC at 2.8 kW. The polypropylene chassis, measuring 635 mm x 600 mm x 1,055 mm (25 inch x 23.6 inch x 41.5 inch) is robust and lightweight for buoyancy and lack of corrosion. The robot's launch weight is 100 kg (220.5 lb), payload is up to 15 kg (33 lb), and top speed is more than 3 knots. 6,400 lumens of LED lights with variable density can be tilted to vary intensity, linked to the video camera's 180-degree tilting mechanism. Data and video are transmitted via F2 fiber optics. Powered by five magnetically coupled thruster units with a combined forward thrust of 50 kgf, the Seaeye Falcon DR has a 1:1 power to weight ratio. Standard sensors include auto depth and heading, pitch and roll, and compass. (Source: Saab)
Ann, watch some of those fish in the big aquarium at your local zoo. There are a few of them that are huge when viewed from the side, and they really do become hard to see when they turn and swim away. My guess is that it is that way to confuse predators.
Rob, sometimes efficiency and streamlining are not the only consideration. Watch some of those fish at the aquarium, some very big fish disappear when they are viewed from the front or the rear. And you don't see very many fish with missile launching abilities.
William is right about shape mattering even more in water than it does in air as far as a fish--or a robot's--speed, maneuverability, and efficiency and therefore power consumption. Just think how much harder it is to swim through water than to walk through air, and the muscles swimming gives your arms as a result.
Rob, shape matters a whole lot in the water and under it, much more than it matters in air. Not only that the greater density takes a lot more power to move it out of the way, but also that the friction of moving through water is greater. One large difference though is that water is generally not compressible,at least not like air.