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The vitelline envelope of Atlantic halibut (Hippoglossus hippoglossus) is composed mainly of two major and two minor proteins. Estradiol-17ß induces the two major vitelline envelope proteins in halibut of both sexes. These proteins were also found in plasma of vitellogenic females. The origin of the two major vitelline envelope proteins is not restricted to the ovary, as male halibut synthesize these proteins after treatment with estradiol-17ß. Individual female halibut were followed and plasma sampled from May to March. Plasma levels of estradiol-17ß increased in October, peaked in early February, and declined until the last ovulation in March. In October, the two major vitelline envelope proteins were first detected in plasma and the amount remained elevated until early March. Prior to the last ovulation, the amount decreased. Plasma vitellogenin varied in a similar way. The results provide strong evidence that the physiological regulation of the synthesis of the major vitelline envelope proteins in teleosts is controlled by the female sex steroid estradiol-17ß.

Minnows (Phoxinus phoxinus) were exposed in the laboratory to 3 nM Cd (Cd group), 2000 nM Zn (Zn group), or to both metals (CdZn group) in soft water for 142 d. A fourth group was kept with no metals added to the water (Low group). After 80 d, the Cd and Zn groups were statically exposed to 109Cd and 65Zn, respectively, for 24 h. The CdZn group was exposed to both tracers. Fish were sampled for 61 d after the tracer exposure. At the end of the experiment, an increased metallothionein level was detected in the kidney of fish exposed to the metal mixture (Low group: 0.14 nmol/g fish; CdZn group: 0.54 nmol/g fish). However, the fish did not acquire tolerance to the metals because mortality continued at a constant rate during the whole experiment. Metabolism of Cd and Zn was altered in fish exposed to the metal mixture compared with fish exposed to Cd or Zn alone. The main effect was a Zn-induced increase in Cd turnover rate in the fish. Nevertheless, the toxic action of metals was additive, since mortality at the end of the experiment was 24, 32, and 54% in the Zn, Cd, and CdZn groups, respectively.

Potential 1+ smolts of Atlantic salmon (Salmo salar) were reared under three light regimes: simulated natural photoperiod (LDN), continuous light (LD24:0), or a combination of continuous, low-intensity background light and a superimposed simulated natural photoperiod (dual photoperiod, LDD). Growth rate in freshwater was enhanced by LD24:0 and LDD, and changes associated with smoking (increased salinity tolerance, reduced condition coefficient) were advanced under LD24:0. Plasma growth hormone levels were initially high on LD24:0 and LDD whereas on LDN, plasma growth hormone levels increased gradually from February through April. Overall GH levels were negatively correlated with condition coefficient during the final stages of smoking. After 16 mo in seawater, there were no significant size differences among the groups. The incidence of sexual maturation as postsmolts was higher in the LD24:0 and LDD groups whereas the incidence of grilsing was higher in LDN. Results demonstrate the significant influence of photoperiod on growth and smoking in Atlantic salmon. An abrupt increase to continuous light in winter may be sufficient to advance important aspects of the parr–smolt transformation. Dual photoperiod may be a way to combine the increased growth rate observed under continuous light and the normal parr–smolt transformation associated with natural photoperiod.