GoDBY. — (jrrowth uf Broirn Trout in t'd/itt rbtiri/. 51 



rapidly in the third, fourth, and fifth years, whilst in the snow-river fish 

 a good growth is maintained. The growth-curve for the snow-river fish 

 is a typical curve for a sample of which the individuals have migrated to 

 more favourable surroundings at varying ages. Probably no individual 

 fish has a growth-curve of this type, but the average curve is compounded 

 of several different types representing the one-, two-, three-, and four- 

 year-old migrants respectively. The sudden jump during the sixth year 

 in the rain-river curve is the result of two fish only, and no importance 

 attaches to it. 



It may seem rather arbitrary to include the Opihi as a rain river and 

 the Ashley as a snow river. Each of these rivers is more or less on the 

 border-line. Sea-going fish frequent each, and each contains a large number 

 of small fish which have not been to sea, though possibly they may go 

 later. It so happens that all my examples from the Opihi, which were 

 caught in November, 1917, near the junction with the Tengawai, belonged 

 to this latter class, whilst all the Ashley fish were largish fish which had 

 probably been to sea. 



In view of the exceptionally poor growth of the Opihi and Tengawai 

 fish, it would be most interesting to get scales from some of the large sea- 

 run fish for which the Opihi is so famous, and to see whether these represent 

 a later stage in the development of fish which as three- or four-year-olds 

 had averaged only 10 in. to 12 in., or whether they belong to a different 

 race. The matter is of some importance to the South Canterbury Accli- 

 matization Society. If these poorly developed three- and four-year-olds are 

 practically the " parr " stage of the larger sea-going trout the present con- 

 dition of the Opihi is healthy ; if not, then in my opinion it is carrying a 

 stock far in excess of its food-supply.* 



Plate IV, fig. 2, shows a scale from one of the Rakaia fish, and is an 

 example of a very clearly marked scale, which is none the less difficult to 

 read. The first winter band is clearly shown, and so is the second ; but 

 immediately outside the latter is another darkening ; there is then a space 

 indicating rapid summer growth, and the rest of the scale is normal. If 

 this peculiarity existed in one scale only it might be attributed to some 

 accident to or displacement of that particular scale. I have ten scales from 

 this particular fish, and every one of them shows the same peculiarity. 

 It has some meaning if one could only find it out. With some diffidence 

 I offer the following explanation : The fish lived in the stream where 

 hatched — probably the Rakaia — throughout the first year and the second 

 summer and autumn ; when the second winter band was nearly complete 

 it migrated to the sea, and immediately responded to the stimulus of sea- 

 water. The stimulus, however, was short-lived, and winter stagnation again 

 set in, causing the third check. So the second and third checks are really 

 one winter band divided by a short period of rapid growth in winter, due 

 to the tonic effect of sea- water. I have met this same peculiarity in one 

 or two other fish from the Rakaia. 



Peculiarities such as this are not uncommon, and when they occur in 

 one scale they invariably occur in every scale from the same fish, showing 



* Since writing the above I have received scales from two of the large sea-run fish 

 of the Opihi, 26 in. and 201- in. in length. Tlie former ajjijears to have migrated as a 

 yearling when about Gin. long, the latter as a four-year-old (jjossibly three-year-old) 

 when about 10^ in. long. The early growth of this latter corresponds closely with 

 that of the small Opihi fish previously mentioned. A scale from thi.s fish is shown in 

 Plate IV, fig. 1. 



