I would suggest to consult the following publication:

Hoestlandt, H. (ed.) 1991 [ref. 24825]

The freshwater fishes of Europe. Clupeidae, Anguillidae. Aula-Verlag, Wiesbaden. v. 2: 1-447.

In the chapter on Anguilla anguilla, F. W. Tesch discusses and illustrates juvenile stages.

Thank you very much Ronald! I do not have this book. Is there any chance you might photocopy me these illustration?

The body shape of eels can vary depending on the species and life stage. However, in general, the ratio between body height/width and total or standard length in eels is likely to change as the eels grow and mature. Additionally, the specific ratio may vary among different populations and species of eels.

To determine the ratio between body height/width and total or standard length in very small eels, you can take measurements of individual eels using a caliper or ruler. For body height, measure the distance from the dorsal fin to the ventral surface of the eel at its widest point. For body width, measure the widest point of the eel perpendicular to the dorsal-ventral axis. Total length is the distance from the tip of the snout to the end of the tail, while standard length is the distance from the tip of the snout to the posterior end of the hypural plate.

Once you have these measurements, you can calculate the ratio between body height/width and total or standard length by dividing the body height or width by the corresponding length measurement. For example, the ratio between body height and total length would be calculated as:

body height/total length

Similarly, the ratio between body width and standard length would be calculated as:

body width/standard length

Keep in mind that the specific ratio may vary among different populations and species of eels, and that these ratios may change as the eels grow and mature. It may be useful to compare your measurements to published values for similar eel species or populations to determine if your measurements fall within the expected range.

In general, glass eels are thin and transparent, while elvers are slightly thicker and pigmented. The body depth of glass eels and elvers can vary depending on the age and size of the fish, as well as environmental factors such as temperature and salinity. Typically, the body depth of glass eels and elvers is relatively small compared to their total length.

According to a study published in the Journal of Fish Biology, the body depth of glass eels and elvers of Anguilla anguilla varies between 4.8% and 9.4% of their total length. The body depth of early sub-adults in the species can range from 10% to 17% of their total length.

It's worth noting that these measurements may vary depending on the specific population of Anguilla anguilla, as well as the method of measurement and the age and size of the fish being measured.