12 b' Part III. — Thirteenth Annual Report 



the beginning of the season. A low death-rate amongst the spawners 

 while in the pond is of great importance, otherwise the healthy fishes 

 may delay their regular spawning. 



By careful examination of the bottom of the pond daily, any fishes 

 that succumb may be removed ; but a very important point, as has been 

 said, is the careful selection of the fishes during the first few weeks after 

 they have been caught. From the delay in the spawning this season, 

 owing to the low temperature, this was accomplished to a large extent 

 before spawning became general, and no difficulties of the kind mentioned 

 occurred, though the number in it was considerable. The fishes were 

 fed on lugworms (Arenicola marina), gathered on the sands in the 

 neighbourhood, an J an average of about nine pounds were used daily in 

 feeding the fishes. Plaice are extremely fond of this kind of food, the 

 lugworms being put in alive and all eaten ; no parts are left to con- 

 taminate the water. The space above the pond was also this year kept 

 in darkness, the effect of this being to subdue the light to approximate 

 to the natural condition in the sea. By careful examination, I have 

 discovered not only that the plaice spawns at night, as was the case ia 

 1894, but that spawning takes place in the course of a few hours after 

 darkness sets in, and is always completed before midnight. This I was 

 able to determine, not only by examination of the surface water in the 

 pond during the night, but from the fact that in the morning the eggs 

 which were then in the spawn-collector were found to be all advanced in 

 development, and at the same stage. 



Further, while the transparency of the water is of importance in order 

 that the bottom and the fishes may be visible and at any time inspected, 

 it has been found that the spawning is always increased if the water 

 becomes somewhat obscure and dull, — a circumstance also showing the 

 advantage of a darkened spawning pond. 



3. Irregular Spawning (Unfertilised Eggs), and measures 



AGAINST IT. 



It has already been mentioned that an irregular emission of eggs took 

 place at the beginning of the season, a number of the females shedding 

 eggs without getting them fertilised. This being a matter of great impor- 

 tance, it will be of interest to state the probable cause of it, and the 

 measures that can best be taken to prevent loss of eggs in that way. 

 Eggs that are found unfertilised have generally been kept back in the 

 ovaries of the fish after they were ripe and ready for spawning, and 

 they differ in various ways from eggs that are spawned at the proper 

 time. The irregularity is apparently owing to a- voluntary action on 

 the part of the fish, and is, I believe, a consequence of timidity, injury, 

 or insufficient food and water supply. It is of interest to notice that 

 nearly all such individuals have been hurt during the trawling,, and as 

 the irregular spawning mainly took place at the beginning of the season — 

 shortly after the ripe fishes had been caught— the bulk of the unfertilised 

 eggs were no doubt from specimens that were in the most ripe condition 

 when placed in confinement. 



It was only when acclimatised to some extent and supplied with a con- 

 stant and full current of water that the fishes began to spawn in the 

 ordinary way ; at first the percentage of fertilised eggs was small as well 

 as the total,; but it gradually increased both ways. 



This leads to the conclusion that an irregular spawning, such as occurred 

 this year, is first of all due to the late capture of the fishes, when they 

 are already in a ripe condition. The trouble and fright to which taey 

 are exposed makes them try to save the eggs, — which, though ready for 



