Description: Juveniles of the common dentex (Dentex dentex) (2.4 g mean weight), were grown over a 6 week period, fed exclusively on a commercial sea bream diet or an isocaloric moist pellet diet, which was produced on site. Ambient temperature (24.4-26.2 °C) and oxygen content (4.8-5.9 mg/L), as well as the relatively low stocking density (max. 2.62 kg/m3) provided favourable rearing conditions. Survival (63.8% vs 51.6%), specific growth rates (6.1% vs 4.5%) and food conversion efficiency (115.8% vs 76.3%) were considerably elevated in the group fed on moist pellets. The growth performance parameters recorded are considered to be favourable for aquaculture requirements. Agonistic behaviour (particular biting of the tail) was found to be the main cause of the continuous mortality that occurred in both feed groups (78% and 64.8% of total mortality in the dry- and moist-pellet group, respectively). These biting attacks targeted the smallest individuals in a tank, whose mean individual weight made up 49-62% (with dry pellet diet) and 28.9-46.6% (with moist pellet diet) of the respective mean weights. The results indicate a strong relationship between nutrition, size variation and agonistic behaviour in the rearing of cornmon dentex juveniles.

Description: Changes in total volume and volume of the yolk and perivitelline space of Pacific herring eggs were examined throughout incubation at 5°C in relation to salinity of the incubation medium (5, 20, 35‰ S), and after exposure to cadmium (0.05–10 ppm Cd) at 20‰ S. After fertilization and filling of the perivitelline space there was a decline in total egg volume in all salinities until 60–80 hr after fertilization. There followed a period of relative stability of total volume (100–240 hr), then a slow decline until hatching (240–618 hr). There was an inverse relation, between egg volume and salinity at all stages of egg development. Eggs transferred from 20‰ to 5 or 35‰ S, 87.4 hr after fertilization (90% blastodermal overgrowth of the yolk), showed only minor changes in total egg volume within the period of relative stability (100–240 hr). Prior to 80 hr, changes in egg volume appeared primarily to be simpleadjustments to prevailing osmotic and ionic conditions, modified, however, by presumed irreversible changes induced in the egg in relation to salinity experience at, and shortly after, fertilization. Subsequently, between 80–100 hr, egg volume appears to becomeregulated, commencing in the interval between late blastodermal overgrowth and blastopore closure. Yolk volume declined after fertilization, reached a minimum 40–60 hr after fertilization, increased to 100 hr, then decreased in the period of relative stability of total volume — presumably in relation to rapid growth of the embryo. In the latter period, yolk volume appeared resistant to change when eggs are transferred from 20 ‰ to 5 or 35 ‰ S, 87.4 hr, after fertilization. Volume of the perivitelline space reached a maximum after fertilization, then decreased until about 100 hr; between 100 and 240 hr it increased rapidly and was influenced only in a minor way by salinity changes in the incubation medium 87.4 hr after fertilization. Eggs exposed to cadmium in the interval between 1/2 and 30 hr after fertilization showed major reductions in total egg volume; total volume in the period of relative stability (100–240 hr) was much reduced and normal volume was not recovered after removal of such eggs to uncontaminated water at 30 hr.

Description: This paper critically reviews the theoretical and practical implications of adopting the original 'ecological footprint' concept as an index of the sustainability of aquaculture production systems. It is argued that the concept may provide a reasonable visioning tool to demonstrate natural resource dependence of human activities to politicians and the public at large. However, due to its inherent weaknesses, the 'ecological footprint' fails to provide a cohesive analytical tool for management. From an ecological perspective, its two-dimensional interpretation of complex ecologically and economically interacting systems is one major weakness. From an economic perspective, the 'footprint' fails to recognise factors such as consumer preferences and property rights which have a major influence on the allocation and sustainable use of resources. The interactions among social, ecological and economic factors are discussed in an attempt to foster a broader inter-disciplinary view of criteria required for a sustainable use of aquatic resources.