CLUPID: Clupeoid larvae identification (KB-14-012-076)

 

Each year four herring larvae surveys are carried to assess North Sea herring spawning stock biomass and recruitment. These surveys are part of the statutory tasks of the Netherlands. In the samples of these surveys approximately 12.500 individual larvae need to be identified to species. Currently clupeoid larvae identification is done by counting myotoms from head to tail under a dissecting microscope.

 

Because it is difficult to count the myotoms right after the head and at the tail end a method was developed to identify part of the larvae and count numbers of myotomes in that part. An ImageJ macro was developed in which semi-automated larvae can be measured. Due to fixation in formaldehyde larvae are bent. By putting some points over the length of the larvae from the nose to the tail tip lenght is measured. Based on the total length, the part from 30% of the total length to 60% of the total length is identified. In this part the number of myotomes are counted and measured automatically.

 

Unfortunately this number of myotomes is not a measure to distinguish between the clupeoid larvae herring, sprat and pilchard. Sprat has a much lower number of myotomes compared to herring and pilchard, but the latter two species overlap in number and size of the myotomes.

The macro does give the possibility to store individual larvae for quality control.