INTRODUCTORY. 7 



Woodcuts of apparatus which have been found unsuccessful 

 are also given, so that the conditions may be studied, and the 

 apparatus either be improved or avoided altogether. 



The materials principally used consisted of wood, brick, and 

 concrete. Concrete has been found the best material for roofing, 

 as it is absolutely frost-proof, but it is not water-tight, and where 

 this is a consideration it requires to be covered with asphalte or 

 corrugated iron, but the preference must be given to asphalte, as 

 the roof has not usually sufficient fall to ensure corrugated iron 

 being water-tight. 



Brick has been found the best material for inlets and outlets 

 of ponds, a wooden frame being built in which to fix the screens. 

 It is also the best material for building valves in the aqueducts 

 or lines of pipe. Wood is probably the most important of all 

 materials used in fish-culture. The best foreign pine should 

 always be used. Home-grown timber does not last sufficiently 

 well for the purpose, and hardwood is very liable to become coated 

 with saprolegneia. The earth work is very important, and must 

 be constructed under the supervision of a first-class engineer, who 

 should be previously instructed that ponds suitable for fish-culture 

 are required, and not mere dams to hold water. As the latter Avill 

 probably be the only ponds the engineer has had any experience 

 of, this caution must be given before the estimates are calculated. 

 The expense per cubic yard is greater in a pond suited for fish- 

 culture than in an ordinary reservoir, and it must never be 

 forgotten that an ordinary reservoir is anything but suited for 

 fish-culture. The principal difference being that a reservoir is 

 usually deepest at the outlet, and a pond for fish-culture should be 

 deepest at a point about one-third of its length from the inlet, 

 and under no circumstances must the deepest part be nearer the 

 outlet than the centre of the pond. 



This principle has been carefully followed at Howietoun, and 

 the success may be estimated by the annual increase in the pro- 

 duction of the Fishery from laying down 25,205 trout ova in 

 the autumn of 1874, to containing a stock of 282,672 fish in 

 August 1886. 



