368 • The N.Z. Journal of Science and Technology. [Dec. 
all classified under the heading of 44 brown." They grew so rapidly and so 
large that in 1906 they had been caught up to, and over, 201b. in weight. 
In 1903 a consignment of rainbow trout was obtained from the Okoroire 
hatchery : these were young fish of fifty days and upwards. Arrangements 
had been made with the Rotorua Coaching Company to forward the cans of 
young fish from the train direct to Taupo. They travelled all night by 
coach, and were handed over to the care of Captain T. Ryan at the wharf, 
Taupo, and from thence they were distributed by coach and steamer to 
all the streams running into the Taupo Lake. The next season a further 
supply was obtained and distributed in the same manner ; also in 1905 a 
further supply was obtained, and in this way every stream, small and large, 
was supplied with rainbow trout. Captain Ryan estimates that in the 
three seasons mentioned above about 250,000 young trout were liberated, 
or over 80,000 per year. Before the last lot were turned out the trout 
grown from the first lot were reported in every stream. From the numbers 
reported it was quite evident that they were then thriving in a most 
amazing manner. The great mortality that occurs in most streams where 
trout have been placed in New Zealand is non-existent in Taupo. There 
are no ells or other voracious fish to prey upon them in these waters. The 
only enemy they have worth considering is the lake shag. 
For the purpose of showing what is going on now I quote from an 
article written by Mr. W. Arthur, C.E., read before the Otago Institute on 
the 9th July, 1878, and published in the Transactions of the New Zealand 
Institute, vol. 11, page 271. It appears from that article that in 1868 
seventy-five young trout were put into Mr. Young’s mill-race at Palmerston. 
The mill-race has communication with the Shag River. The first specimens 
caught were those taken in 1874, which were placed in the Otago Museum. 
One of these, a male fish, was caught in June of that year, and weighed 
14 lb. A female fish was taken in July of the same year, and weighed 
16*5 lb. In comparing the above dates we find that the greatest possible 
age of these fish could not exceed six years. This indicates an average 
growth of the male fish of 2-3 lb., and for the female 2-75 lb., per year. It 
appears from the same article that even under the most favourable con¬ 
ditions a yearling trout will not weigh more than 1 lb., so that the average 
rate of growth after the first year is even more than what is quoted. 
Female trout have been caught at Taupo which gave an average weight of 
3*5 lb. per year ; but for our purpose we are taking the average rate of 
growth at 2 lb. only per year. Again referring to Mr. Arthur’s article, he 
mentions a healthy fish of about 7 lb. weight yielding close on 6,000 ova. 
This is in agreement with, the usual statements of expert fishers. A female 
trout in good condition will yield ova in the above proportion ; an 11 lb. 
trout is expected to give 9,000 ova. 
We will now return to the consideration of the increase of the 80,000 
rainbow trout liberated in Taupo in January, 1903. To allow for all sorts 
of casualties we will suppose that by January, 1905, only 8,000 survived, 
and of these we would claim 4,000 to be females of at least 4 lb. weight each. 
They would have deposited, according to the above, 12,000,000 ova during 
that season. Remembering the traps and pitfalls that surround the early 
period of a trout’s existence, we would allow that only 120,000 of those 
