Italian researchers believe that a lead pipe piercing the hull of a sunken Roman ship was part of a pumping system that provided on-board fish tanks with a continuous flow of oxygenated water. This contraption may have allowed ships to carry live fish to buyers across the Mediterranean Sea.
Previously, historians conjectured that in ancient times fresh fish were consumed close to where they were caught because refrigeration methods were nonexistent.
"Historians think that before the invention of the freezer, the only possibility to trade fish was to salt or dry it, but now we know that it was possible to move it alive also for quite a long distance," said Carlo Beltrame, a marine archaeologist at the Ca' Foscari University of Venice in Italy, reports Livescience.
The analysis has been published in the International Journal of Nautical Archaeology.
Nearly 2,000 years old, the vessel was noticed 6 mi off the coast of Grado in northeastern Italy in 1986, recovered in 1999 and is now at the Museum of Underwater Archaeology in Grado. Measuring some 16.5 m in length, the vessel held hundreds of vase-like containers carrying processed fish such as sardines and salted mackerel, reports Nature.
Beltrame and his colleagues believe the pipe on the ship must have been connected to a piston pump and one-way valves that pushed water between reservoirs and supplied a fish tank.
Even though historians know the Romans had access to such technology, this is the first time it has been detected on their ships, and the pump itself was not found in the wreckage.
The researchers estimate that a ship like the Grado wreck could have hosted a tank with a capacity of about 4 m3 of water and 200 kg of live fish.
A constant oxygen supply would have been required to keep the fish alive and the water in the tank replaced every half an hour. The researchers calculated that the piston pump could have supported a flow of 252 l per min -- allowing the water to be replaced in just 16 min, which helps validate their theory.
But Tracey Rihll, a historian of ancient Greek and Roman technology at Swansea University in the UK noted the absence of direct evidence for a fish tank. Still, she said the pipe could have been used for that purpose in the ship's younger days.
The researchers "dismiss fire-extinguisher and deck-washing functions too easily in my view," she cautioned.
Rihll added that literary and archaeological evidence points to the possibility that live fish were transported by the Greeks and Romans "on a small but significant scale."
By Natalia Real