Early ontogeny of the spotted wolffish (Anarhichas minor Olafsen)

Abstract

This study illustrates the embryo development of the spotted wol⁄sh (Anarhichas minor Olafsen), an interesting candidate for cold-water aquaculture. The egg morphology (semitransparent, yellow-white with numerous oil droplets in the yolk), size (5.4^6.5 mm) and long embryogenesis (c. 800^1000 d1, depending on temperature) of A. minor are very similar to Anarhichas lupus. Cleavage is slow, and the ¢rst cell divisions take place at 12 h at 8 1C. After 12 days the 2mm embryo with the ¢rst somites is laid down and the blastopore starts closing. The fat globules in the yolk fuse into one after 22 days, and after 30 days eye pigmentation is noticeable. After 44 days, eye pigmentation is strong, the digestive tract folded and a green gall bladder can be noted in the now 11-mmlong embryo. One week later the blood is brightly red, the intestine is pigmented and the lower jaw is well developed. Premature hatching may occur from this stage. After 58 days vascularization of the yolk is complete, capillaries are noted in the ¢n fold, the ¢rst ray rudiments are established in the tail and pectoral ¢ns, and the four gill arches are covered by the operculum. The preanal ¢nfold is reduced after 72 days, stomach and gill ¢laments are formed, and six pigmented rows are noted on the 17-mm-long embryo body. After 86 days all ¢n rays are seen and the digestive tract is intensely pigmented and folded. Hatching (normal) starts after 110 days and may last for 2^3 weeks. Late embryos and early larvae of A. minor have more distinct bands of pigment along the body compared with the closely related A. lupus. An increase in both length and weight of the embryos in individual batches occurs during the hatching period.

A review of the culture potential of spotted wolffish Anarhichas minor Olafsen

“…genetic variation among egg batches causing partly contradicting results, may be argued. Still, it is concluded by Falk-Petersen and Hansen (2003) that incubation at both 6 and 8°C, as well as at ambient temperatures(6-8°C decreasing towards hatching to about 3°C) gives satisfactory survival during the incubation period. Furthermore, it is clear that incubation temperature affects survival and growth after hatching (Hansen and Falk-Petersen, 2001a).…”

“…The eggs in the ovarian fluid are fertilized by undiluted sperm from at least two or three males, and then left for 2-3 h after stirring to ensure maximum fertilization. Male spotted wolffish produce very restricted amounts of sperm, varying from 0.5 to 6 ml, but good producers may often be stripped several times at weekly intervals during the reproductive season which can last for 3 to 4 months (FalkPetersen and Hansen, 2003). Subsequently, eggs are transferred to seawater and gently stirred for the next couple of hours to prevent them from sticking together and thereafter carefully spread in a single layer in small upstream incubators to facilitate the tending operation (Falk-Petersen et al, 1999;Falk-Petersen, 2001a, b, 2002;Falk-Petersen and Hansen, 2003).…”

“…In general, broodstock of spotted wolffish is recommended to be kept at temperatures around 4-6°C throughout the spawning season, although it is not yet fully understood how ambient temperature during final stages of maturation affects subsequent embryonic development and survival (Falk-Petersen and Hansen, 2003). Hansen and Falk-Petersen (2001a) compared survival and early development in spotted wolffish eggs and larvae as an effect of incubation temperature and female broodstock holding temperature.…”

Population Genetic Structure of the Spotted Wolffish, Anarhichas minor, in the North Atlantic

“…code, with haplotype A being the most common, and the remainder ranked in the order in which they were found for each restriction enzyme. Composite restriction enzyme patterns were then given a numerical code (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) to facilitate data handling. Data were converted into a binary format, coding restriction sites as presence/absence (1/0).…”

“…In nature the species displays rather slow growth (Østvedt FSH 1963 [3] Templeman JNAFS 1986) [4], and maturation does not occur until after 7-9 years. It has internal fertilization and the eggs (5-6 mm diameter) are collected in a ball and probably guarded by the male until hatching, which occurs after approximately 800-1000 D° (day-degrees) (Falk-Petersen AR 2003) [5]. The larvae hatch as well developed individuals (20-24 mm), live pelagically for several weeks and settle in benthic environments at 4-6 cm.…”