Seasonal changes in the pituitary‐ gonad axis of feral goldfish, Carassius auratus L., from Ontario, Canada

Abstract

Apparently healthy, feral goldfish, Carassius auratus L., were collected from a pond in Cambridge, Ontario from March until November 1981, and during April 1982. Based on histological examination, oocyte development was divided into five stages and the reproductive cycle into five periods. The origins of oogonia and the atresia process were examined. The gonadosomatic index (GSI) was found to be an accurate indicator of ovarian activity in the feral population. Based on the GSI, proportion of various oocyte stages and egg size, females older than 2 years appeared to spawn during two periods, May to June and late August; 2-year-old fish spawned in the first period. There was a reduction in the density, abundance and nuclear diameter of presumptive pituitary gonadotrops in early August, after the completion of ovarian development and before the completion of spawning.

Abnormal pituitary‐gonad function in two feral populations of goldfish, Carassius auvatus (L.), suffering epizootics of an ulcerative disease

“…Moreover, incidental captures of goldfish in 1974 and 1975 in gillnets with mesh size as large as 5 inches The population of goldfish collected from Hamilton Harbour showed no seasonal changes in GSI, ovarian stages or testicular development which could be considered consistent with successful gamete release. Moreover, there was a higher prevalence of atresia and necrosis of ova than reported previously for successfully spawning goldfish (Munkittrick & Leatherland 1984). The rare individual female fish which successfully released eggs did so in early September, well after previously reported spawning times, and the ova they released appeared non-viable.…”

“…The pituitary gonadotrops of the Hamilton goldfish showed little evidence of a seasonal change in activity or abundance, and in this regard differed markedly from the situation found in a comparable reproductively viable goldfish population (Munkittrick & Leatherland 1984). The high apparent gonadotrop activity in the Hamilton Harbour population even during winter months indicates a dysfunction of the hypothalamicpituitary-gonad axis, which prevents the release of mature eggs, but not their development or maturation.…”

“…In the goldfish collected from Hamilton Harbour the proximal pars distalis gonadotrop cells were relatively more abundant and more numerous than in a successfully reproducing population of goldfish sampled during comparable seasons (Munkittrick & Leatherland 1984). There were no significant changes in the abundance of gonadotropic cells throughout the sample period.…”

“…Five stages of egg growth were recognized (Munkittrick & Leatherland 1984). Stage I oocytes stained weakly with haematoxylin and included developing ova which had completed the last mitotie oogonial division and attained a size of approximately 10 ^m, as well as oocytes in the 'chromatin nucleolus' or 'perichromosomal nucleolus stage' (Yamazaki 1965) which were characterized by a conspicuous nucleolus with chromatin threads.…”

Growth and reproduction of introduced goldfish Carassius auratus in small ponds of southeast England with and without native crucian carp Carassius carassius

“…males ‚ no. females) of introduced goldfish Carassius auratus populations from various sources: 1) present study, small ponds; 2) Munkittrick and Leatherland (1984), a pond of 200 · 60 m; 3) Lorenzoni et al (2007), with detailed information provided by M. Lorenzoni; 4) _ Izci (2004); 5) Patimar (2009); 6) Mitchell (1979), a backwater of the River Murray at Cobdogla, the Millbrook Reservoir and a small farm dam at Uraidla; 7) Morgan and Beatty (2007), with mean values for both sexes calculated from the reported data…”