... Science Frontiers ONLINE No. 74: Mar-Apr 1991 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Eel Oddities Garter snakes are reknowned for their habit of congregating in large, writhing masses, but we never heard of "eel balls" until A. Gardiner mentioned them in a recent issue of the Fortean Times. "These [eel balls] are recorded in Christopher Moriarty's excellent Eels: a Natural and Unnatural History (David and Charles, 1978). Moriarity cites Pliny as the earliest historical reference. According to him, Eel Balls occur in Lake Garda, Italy, when it has been storm-tossed by the effects of the October 'Autumn star'. Smitt in his Scandanavian Fishes (1895) says that eels ... themselves together in bunches 'up to a fathom in circumference' and are seen rolling along the stream beds, or, strangely, resting in this position. On 17 August 1935, fishery scientist J.C . Medcof observed, in the outflow of Lake Ainslie in Nova Scotia, 'three splendid clumps of Eels, half a metre in diameter, 30 to a clump, knotted tightly and remaining motionless in the rushes.' Medcof mentions that Eel Balls are sometimes free floating on the surface, which suggests formation with an air pocket or some communal control of air bladders. He says that this behavior occurs before eels 'silver' prior to the spawning migration. The record of Eel Balls in Nova Scotia proves that this behaviour is not confined to the European Eel." (Gardiner ...
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... . 89: Sep-Oct 1993 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Why do electric fish swim backwards?This is not a trick question like the one about the chicken crossing the road. To understand the answer to the electric fish puzzle, we must restrict the discussion to those fish with active electric sensing systems. This group includes electric eels, South American knife fish, and African elephant snout fish. All of these have evolved, in a remarkable instance of parallel evolution, the capability of generating pulses of electricity. These pulses (up to 1,000 per second) radiate through the surrounding water. Prey and other nearby objects distort these oscillating electric fields. Electroreceptors on the fish and a sophisticated data processing system convert the ... distortions into an "image" of the surroundings. M. and S.J . Lannoo, of Ball State University, have watched the black ghost knife fish, which plies murky Amazon waters, approach likely prey tail first. Swimming backward using an elongated belly fin, the knife fish slowly cruises past its potential victim. If the electrical image looks appetizing, the knife fish grabs its dinner with a forward lunge as it appears in front of it. "The researchers suggest that the fish swims past objects in order to scan them with its electroreceptors. This is the only way the fish can identify prey because an electric sense cannot be focussed like an eye. But if the fish carried out its scan by swimming forwards, the prey would end up at its tail. The fish ...
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