  We present the detection of bright [CII] emission in the z=4.76 submillimetre
galaxy LESS J033229.4-275619 using the Atacama Pathfinder EXperiment. This
represents the highest redshift [CII] detection in a submm selected,
star-formation dominated system. The AGN contributions to the [CII] and
far-infrared (FIR) luminosities are small. We find an atomic mass derived from
[CII] comparable to the molecular mass derived from CO. The ratio of the [CII],
CO and FIR luminosities imply a radiation field strength G_0~10^3 and a density
~10^4 cm^-3 in a kpc-scale starburst, as seen in local and high redshift
starbursts. The high L_[CII]/L_FIR=2.4x10^-3 and the very high
L_[CII]/L_CO(1-0) ~ 10^4 are reminiscent of low metallicity dwarf galaxies,
suggesting that the highest redshift star-forming galaxies may also be
characterised by lower metallicities. We discuss the implications of a reduced
metallicity on studies of the gas reservoirs, and conclude that especially at
very high redshift, [CII] may be a more powerful and reliable tracer of the
interstellar matter than CO.
