Effect of temperature on hatching and growth of cuban gar (Atractosteus tristoechus) larvae
Hatching success, growth, development and survival of Cuban gar ( Atractosteus tristoechus ) larvae were examined at different temperatures (26, 28 and 30 o C) up to 18 days after hatching (DAH). The time to hatching was inversely related to the incubation temperature (87, 100 and 111 h). Larval survival at the time of hatching was significantly lower at 30 o C (50.3 %), coinciding with the highest larval mortality (30.2 %). Growth rates were 1.75 mmd -1 -10.4 % d -1 at 26 o C,1.30 mm d -1 -10.2 % d -1 -1 at 28 o C and 1.40 mm d -1 -10 % d -1 at 30 o C. Three similar critical periods were identified: 0-6, 7-11 and 12-18 DAH. During the first period, a similar increase in weight and a significant increase in total length occurred, mainly at 30 o C, indicating a more efficient reconversion of the yolk reserves. Later, growth was equally slow, corresponding with the transitional period from endogenous to exogenous feeding, indicating a similar physiologic pattern regardless of incubation temperature. Weight and length increased during the last period, with the greatest increase at 26 o C in contrast with the lowest gain at 30 o C. The inflexion points of many morphometric characters and the developmental stages accelerated with the increasing temperature. Although it was impossible to determine the optimal temperature, it was evident that 26 o C favored hatching success and larval growth.
Ontogenetic allometries and shape changes in the suckermouth armoured catfish Ancistrus cf. triradiatus Eigenmann (Loricariidae, Siluriformes), related to suckermouth attachment and yolk-sac size
Early life-history stages of the loricariid catfish Ancistrus cf. triradiatus are described, from prehatch embryos to juveniles. The descriptions, as well as metric characters, indicate that the freeswimming embryonic stage is followed directly by the juvenile stage, without a true larval stage or metamorphosis. Intense, but gradual ontogenetic head-shape changes are present during the embryonic and free-living embryonic stages: the suckermouth gradually shifts from an almost rostral to a ventral position. The external and internal transformations related to this shape change are considered an adaptation to both the loricariid algae-scraping feeding mode and the need of suckermouth functioning from the moment of hatching, when a ventrally situated suckermouth would be disadvantageous, as a large yolk sac is present. # 2008 The Authors Journal compilation # 2008 The Fisheries Society of the British Isles
Inhibition of Root Growth and Polyamine Metabolism in Sunflower (Helianthus annuus) Seedlings Under Cadmium and Copper Stress
Although sunflower is usually regarded as a highly tolerant crop, impairment of root growth at initial stages of plant development may result in poor crop establishment and higher susceptibility to pathogen attack. In order to evaluate if Cd2+ and Cu2+ may impact on sunflower germination and initial root development, a pot experiment under controlled conditions was carried out. Possible involvement of polyamine metabolism in sunflower response to these stressors was also investigated. Although Cd2+ and Cu2+ treatments affect neither seed germination nor radicle emergence, sunflower seedlings grown in the presence of these heavy metals showed significant inhibition of root growth, being this inhibition greater for Cd2+. Both metals caused significant increases in proline contents at the highest concentrations tested (0.5 and 1 mM), and these increments were more pronounced for Cd2+ treatments, especially between days 3 and 10. Metals also increased putrescine (Put) contents at all concentrations assayed from the seventh day onward, causing no variations on this polyamine time-course pattern. Spermine and spermidine contents, however, were increased only by 1 mM Cd2+. Arginine decarboxylase seems to have been the enzyme responsible for Put increases under both metal treatments. This work demonstrates that initial root growth of sunflower seedlings may be significantly impaired in Cd2+ or Cu2+ contaminated soils. It also shows that polyamines are key biological compounds, which are probably involved in signaling pathways triggered under stress environmental conditions.