Abstract: Rearing temperature was used to monitor muscle growth patterns of sea bass Dicentrarchus labrax, L. from hatching to the commercial size (350 g, 30 cm). At this moment, the white muscle cellularity, proximate composition and organoleptic parameters of the fillet were analysed to evaluate the influence of temperature on the structure and quality of the commercial product. One ambient (A/A) and three warm regimes of temperature were compared. In warmed tanks temperature was raised to 19 °C: during the larval period (W/A), only during the cool seasons (winter and early spring) (A/W), or both during the larval period and cool seasons (W/W). High temperature during the larval period was positive for an advanced yield of fingerlings and early juveniles. Winter heating of juveniles also advanced the time to reach 200 g by 25 days. However, independently of the thermal regime all fish attained the commercial size at approximately 600 days. Temperature modulated the rates of hypertrophy and hyperplasia of white muscle fibres throughout the larval, fingerling and juvenile periods, such that at commercial size the number and size distributions of muscle fibres varied depending on the previous thermal story. Thus, the density of muscle fibres (number/mm2) was maximum in tank W/A (212.19 ± 8.77) and minimum in W/W (151.95 ± 8.7) (p < 0.001). The proximate composition varied for moisture and protein content, but independently of temperature, all the sensorial attributes of cooked flesh (firmness, juiciness, fattiness, chewiness, flavour and odour) were similar. Thus, no correlation between muscle fibre size and flesh texture was found. Compensatory growth of fish reared at ambient temperature and the uniformity of the proximate composition and sensorial properties evaluated by panellists minimized the impact of temperature on both the time at harvest and the quality of the commercial product.
Keywords: Fish; Muscle growth; Temperature; Sea bass; Flesh quality
Abstract: Gibel carp (Carassius gibelio Bloch, 1782) is regarded as a pest species in most aquatic ecosystems where it occurs and eradication methods have not been very promising. However, because of the close taxonomical proximity between gibel carp and cultured cyprinids, the pituitary of gibel carps could be exploited for hormonal induction of artificial propagation in aquaculture. Thirty-two mature female gibel carps were electrofished in Lake Pamvotis (northwest Greece) in
March 2005 and their pituitaries were collected and processed. The carp luteinizing hormone (cLH) levels in 20 pituitaries were assayed and found to correlate with total body weight, total length, dry pituitary weight, and gonadosomatic index. The cLH levels were in the same range as cLH levels in pituitaries of common carp (Cyprinus carpio Linnaeus, 1758) used in Israeli hatcheries for artificial propagation. Hence, it may be possible to use gibel carp pituitaries for hormonal induction in cyprinids, with total weight of the gibel carp as a field criterion for selecting pituitary donors.
Abstract: The populations of Pseudophoxinus epiroticus, endemic to Lake Pamvotis, Greece, collapsed between 1990 and 1998 and was about extinct in 2001. There are signs that it might now be in an early recovery stage.
Abstract: Gibel carp Carassius gibelio exhibits gynogenetic reproduction by utilising the sperm of other species. Over a period of twelve months, the spawning behaviour of gibel carp in Lake Pamvotis (NW Greece) was monitored. Females almost exclusively (97.7%) composed the population, indicating gynogenesis using the sperm of other species. Reproduction began in March and lasted through April. Contrary to the situation reported in other ecosystems, common carp was not present in the spawning grounds during the spawning season of gibel carp; the
most abundant other species present at that time was Rutilus ylikiensis. To evaluate the sperm donating results of R. ylikiensis as compared with other species of the lake, eggs of gibel carp were fertilised with sperm of R. ylikiensis
(group 1), Carassius auratus (group 2), and Cyprinus carpio (group 3). Also, gibel carp eggs attached to natural substrates were collected from the spawning grounds (group 4). Hatching success ranged from 9-29% in group 4, compared to 95-98% in groups 1, 2 and 3. Over a period of 60 days after hatching, mortality ranged from 35% (group 1) to 56% (group 3), and specific growth rate from 2.4% (group 3) to 2.9% (group 1). We conclude that gibel carp can successfully utilise sperm of ylikiensis roach, which was the best available sperm donor option for the gynogenetically reproducing gibel carp of the lake.
Abstract: Chromosome engineering was used to develop lines that expressed the stable phenotypic characteristics of goldfish, Carassius auratus (var. oranda). To obtain androgenetic individuals, carp eggs were irradiated and fertilized with sperm from goldfish bearing telescopic eyes. The fertilized eggs were divided into four groups and three of them were subjected to heat-shock treatment at 42 degrees C for 2.0 min at 34, 37 and 40 min after fertilization. All groups exhibited low viability of embryos and after hatching the embryos were severely deformed on the head, yolk sac and tail and exhibited 100% mortality, within 2 days after hatching. To obtain gynogenetic individuals, a thin layer of carp milt was subjected to ultraviolet irradiation for 26 min to neutralize its genetic material and used to fertilize a mixture of eggs derived from three different variations of C. auratus individuals with characteristics such as round fat body, triple tail, red and black colour and telescopic eyes. The fertilized eggs were divided into six groups and five of them were subjected to heat-shock treatment at 39.5 degrees C for 2.5 min at 15 (group 2), 20 (group 3), 30 (group 5) and 45 (group 6) min after fertilization. The percentage of fertilized eggs that survived ranged from 20 to 50% and the percentage of larval survival in groups 2-5 was 22-28% with lower levels in groups 1 and 6, ranging from 10-12%. However, 40-60% of the larvae exhibited severe deformities on the head, yolk sac and tail, whereas the rest developed normally. Fish with the typical oranda phenotype were observed in all the groups and about 1% of the fish were characterized by a triple tail but there was no fish with telescopic eyes. The results indicate that gynogenetic individual goldfish can be produced but that the induction of androgenesis requires further improvement of the techniques.
Abstract: The maximum activity of cytochrome c oxidase in fish muscle extracts
is compared with the activity obtained using methods employed
previously. The results indicate that assays of the enzyme made in
earlier studies can result in a considerable underestimate (by more
than 90%) of the enzyme content in fish muscle. Accurate measurements
of the oxidase activity depend upon full activation of the enzyme by
the detergent (e.g. Triton X=A9100) treatment of muscle homogenates;
the use of optimal assay conditions; and the calculation of k, the
first-order velocity constant of the oxidase reaction.
