176 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



month; in our Gulf, egg production (as evidenced 

 by the numbers of eggs taken in our tow nets) is at 

 its height in July and August and continues 

 through September, though less freely, with 

 October 22 as our latest date. Similarly, the 

 Canadian Fisheries Expedition found no silver 

 hake eggs in Nova Scotia waters east of Cape 

 Sable in May, but many in July. 



It is impossible to establish the exact tempera- 

 ture at wbich silver hake are spawning at any 

 particular station without knowing at what level 

 ripe fish are in the water, which may be anywhere 

 between the surface and the bottom with this 

 species. It may be definitely stated, however, 

 that they never spawn in as cold water as cod and 

 haddock usually do in the western Atlantic. In 

 1915, for example (a representative season), it 

 was not until the entire column of water was 

 slightly warmer than 41° F. at the locality in 

 question that we found the first silver hake eggs 

 in our Gulf. And if the parent fish were in the 

 upper water layers, as they may have been, all the 

 rich spawnings we encountered in the Gulf during 

 that year, and during the next, took place in tem- 

 peratures considerably higher still. Similarly, the 

 silver hake eggs towed off Halifax by the Canadian 

 Fisheries Expedition in July 1915, and off Shel- 

 burne, Nova Scotia, by the Grampus on September 

 6 of that same year may have been spawned in 

 water warmer than 50° F., there being no need to 

 assume that the parent fish were lying in the 

 colder bottom stratum. As the spawning season 

 draws to its close, in September and October, the 

 minimum temperatures for most of our egg stations 

 have been higher than 46°, with one (our latest 

 record for the season) as warm as 57° F. at all 

 depths. These data point to 41° to 45° F. as the 

 lowest temperature limit for the spawning of the 

 silver hake, with most of the eggs produced at 

 45° to 55° F. 



In the case of any fish producing buoyant eggs 

 the tendency of the latter to rise (unless counter- 

 acted by active vertical circulation of the water) 

 insures that their development shall take place at 

 the temperature of the upper stratum of water, 

 not at that of the deeper levels where they were 

 spawned. And the silver hake is no exception to 

 this rule. While we have towed its eggs in June, 

 when the surface was still only about 42° F., most 

 of the egg records, and all our rich catches, were 

 all made where the upper 5 fathoms or so were 



warmer than 50° and usually warmer than 55° F., 

 with the temperature of the immediate surface 

 60° or higher in most cases. Similarly, silver 

 hake eggs taken off Halifax by the Canadian 

 Fisheries Expedition in July 1915, and off Shel- 

 burne, Nova Scotia, by the Grampus on September 

 6 of that year, may well have been in water at 

 least as warm as 53° F., there being no reason to 

 suppose they were far below the surface. 3 ' All 

 this suggests that incubation does not proceed 

 normally in water cooler than about 50°, and that 

 it is most successful in temperatures as high as 

 55° to 60° F. This evidence that while the eggs 

 of the silver hake may be spawned in low tem- 

 peratures, a comparatively warm surface layer is 

 necessary for their later development, offers a 

 reasonable explanation for the failure of this fish 

 to breed successfully along the New Brunswick 

 shore of the Bay of Fundy, where active vertical 

 circulation maintains surface temperatures as low 

 as 50° to 55° F. throughout the summer, at least 

 in most years. At the other extreme, the failure 

 of the eggs that had been fertilized artificially to 

 develop in the hatchery at Woods Hole in August 

 temperatures points to 65° to 70° F. as the upper 

 limit to successful incubation. 



According to Kuntz and Kadcliffe 32 only part 

 of the eggs mature at one time, but we know of 

 no estimate of the number of eggs a single female 

 may produce. The eggs are buoyant, transparent, 

 about 0.88 to 0.95 mm. in diameter, with a single 

 yellowish or brownish oil globule of 0.19 to 0.25 

 mm. Incubation is rapid; Kuntz and Kadcliffe 

 assumed a duration of 48 hours at Woods Hole, 

 but it has not been determined for the cooler 

 waters in the Gulf of Maine. The larvae are 

 about 2.8 mm. long at hatching, slender, with 

 small yolk sac, and they are made recognizable 

 by the fact that the vent is located on one side, 

 near the base of the larval fin fold, as is the general 

 rule in the cod family, not at its margin as in most 

 larval fishes, and that the trunk behind the vent 

 is marked with two black and yellow cross bars. 

 The dorsal and anal fins and the caudal fin have all 

 assumed their definite outlines by the time the 

 little fish is 10 to 11 mm. long, and fry of 20 to 

 25 mm. begin to resemble their parents in general 

 appearance. 



31 These catches were all made either at the surface or in oblique hauls 

 with open nets. 



>» Kuntz and Radcliffe (Bull. U. S. Bur. Fish., vol. 35, 1918, p. 109) describe 

 the spawning and early development. 



