  Context. Type II radio bursts are solar radio burst associated with coronal
shocks. Type II bursts usually exhibit fine structures in dynamic spectra that
represent signatures of accelerated electron beams. So far, the sources of
individual fine structures in type II bursts have not been spatially resolved
in high-resolution low-frequency radio imaging. Aims. The objective of this
study is to resolve the radio sources of the herringbone bursts found in type
II solar radio bursts and investigate the properties of the acceleration
regions in coronal shocks Methods. We use low-frequency interferometric imaging
observations from the Low Frequency Array (LOFAR) to provide a spatially
resolved analysis for three herringbone groups (marked as A, B, and C) in a
type II radio burst that occurred on 2015 October 16th. Results. The
herringbones in groups A and C have a undiversified frequency drift direction
and propagation direction along frequency. They have similar value of frequency
drift rates corresponding to that of type III bursts and previously studied
herringbones. Group B has a more complex spatial distribution, with two
distinct sources separated by 50 arcsec and no clear spatial propagation with
frequency. One of the herringbones in group B was found to have an
exceptionally large frequency drift rate. Conclusions. The characteristics
deroved from imaging spectroscopy suggest that the studied herringbones
originate from different processes. The herringbone groups A and C most likely
originate from single-direction beam electrons, while group B may be explained
by counterstreaming beam electrons
