Since the collapse of the pelagic fisheries off southwest Africa in the late 1960s, jellyfish biomass has increased and the structure of the Benguelan fish community has shifted, making the bearded goby (Sufflogobius bibarbatus) the new predominant prey species. Despite increased predation pressure and a harsh environment, the gobies are thriving. Here we show that physiological adaptations and antipredator and foraging behaviors underpin the success of these fish. In particular, body-tissue isotope signatures reveal that gobies consume jellyfish and sulphidic diatomaceous mud, transferring "dead-end" resources back into the food chain.

Live yolk-sac halibut, Hippoglossus hippoglossus (L.) larvae from rearing experiments at Austevoll Aquaculture Station, Norway, were examined from hatching to past first feeding for developmental morphology and behaviour. The findings include development of the respiratory and circulatory organs, eye pigmentation, mouth formation, organs of the digestive system and the process of yolk absorption, as well as swimming speed and activity levels.A stomodeum is not present at hatching although drinking is possible through a pair of branchial pits which gradually develop into the operculum and gill basket. The mouth normally opens slowly, the gape being restricted by a transverse septum until bones are formed. The amount of time spent swimming varies from less than 15% of the observation period during the first 2 weeks after hatching to between 70 and 100% around the seventh week after hatching, when individual differences become more apparent. Larvae generally react with a burst of swimming when two come into contact. Speed and duration of swimming seems to be correlated with development of eye pigment, heart size and fin formation. The yolk-sac period is divided into four stages.

Teleost fish are more diverse than any other vertebrate group, and yet only a limited number of species are fished and farmed globally. Efforts to expand the quantity and diversity of fish produced are hampered by the extreme diversity of ontogenetic responses of fish, especially during larval development. This review looks at advances in molecular phylogeny, endocrine and nutrient influences and long-term studies of the phenotypes of commercially important fish to put the sources and consequences of this plasticity into context. This nested context of evolutionary forces of the fish-specific genome duplication, epigenetic influences, ontogenetically conserved processes like metamorphosis and cell determination is further presented in relation to how fish larvae translate the environment into somatic signals, the teleostian diversity of internal processes like sex differentiation and somatogenesis, and the long-term practical consequences of changes in timing or anthropogenic influences. This review aims to present a new baseline of knowledge of marine fish larvae which is useful to scientists, managers and producers.

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Atlantic halibut larvae were fed docosohexanoic acid-(DHA) selco enriched Artemia (RH-cysts) or wild zooplankton in duplicate tanks from first-feeding and 60 days onward. The zooplankton were collected from a fertilized sea water pond and consisted mainly of different stages of Eurytemora affinis and Centropages hamatus. There were no differences in survival, or in growth during the first 45 days of feeding, between larvae fed the two prey items, but the larvae fed Artemia showed much higher incidence of malpigmentation and impaired eye migration than larvae fed zooplankton. The prey organisms contained similar amounts of dry matter and protein, but Artemia was higher in lipid and glycogen than the zooplankton. Larvae fed Artemia were higher in both glycogen and lipid than the zooplankton-fed larvae towards the end of the feeding period. There were large differences between the prey organisms in the concentrations of essential fatty acids (% of total fatty acids) which was reflected in the fatty acid composition of the larval body. It is concluded that the macronutrient composition of Artemia in the present study was probably within the optimal range for promotion of growth and survival in young Atlantic halibut. The concentration of n-3 HUFA, and especially DHA, is however, very much lower in enriched Artemia than in copepods, and may be one of the factors triggering developmental errors in Atlantic halibut. KEY WORDS

The eye and retina in Atlantic halibut (Hippoglossus hippoglossus), from early yolk sac stages through metamorphosis, were examined after dissection by light microscope, and, for selected stages, by transmission electron microscope. At hatching the eyes were transparent and the retina undifferentiated. The retina differentiated slowly in sectors, and appeared functional around 150 degree-days (d°) posthatching (about 50% yolk absorption). This timing coincided with the development of functionality in other organs and observations of ability to feed. At the commercial time of first feeding (about 210 d° or 70% yolk absorption) the eyes were fully pigmented. Eye migration started at approximately 80 days posthatching, concurrent with the reorganization of the cones in the outer retina from single rows into a square-type cone mosaic. At 130 days, when metamorphosis was complete, the retina contained groups of rods and appeared to be mature, but until this stage, cones were the primary photoreceptor. The formation of a cone mosaic, recruitment of rods, and increasing size of the eye all indicated increased visual sensitivity at the time of settling. The results suggest that in culture, larvae can see to feed after 150 d°, and at settling, they can be successfully fed under dim light.Résumé : L'oeil et la rétine de flétans (Hippoglossus hippoglossus), des premiers stades de la larve vésiculée jusqu'à la métamorphose, ont été examinés après dissection au microscope optique et, pour certains stades, au microscope électronique à transmission. À l'éclosion, les yeux sont transparents et la rétine n'est pas encore différenciée. Elle se différencie lentement par secteurs et paraît être fonctionnelle environ 150 degrés-jours (d°) après l'éclosion (vitellus absorbé à environ 50 %). Ce moment coïncide avec l'entrée en fonction d'autres organes et la capacité observée de s'alimenter. Au moment du premier repas en élevage commercial (environ 210 d° ou 70% d'absorption du vitellus), les yeux ont complètement acquis leur pigmentation. Leur migration commence environ 80 jours après l'éclosion, au moment de la réorganisation des cônes vers la surface de la rétine, soit d'un alignement en rangées simples à une mosaïque de carrés formés de ces cônes. Au bout de 130 jours, une fois la métamorphose complétée, la rétine contient des groupes de bâtonnets et paraît être complètement fonctionnelle, mais jusqu'à ce stade, les cônes constituent les principaux photorécepteurs. La formation d'une mosaïque de cônes, le recrutement des bâtonnets et le grossissement de l'oeil pointent tous vers une sensibilité visuelle accrue au moment de la migration vers le fond. Les résultats suggèrent qu'en conditions d'élevage, les larves voient assez bien pour s'alimenter au bout de 150 d° et qu'au moment de s'installer au fond, elles voient assez bien pour s'alimenter sous une lumière tamisée.[Traduit par la Rédaction]

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Atlantic cod Gadus morhua larvae reached four-fold (at low larval density) to 11 fold higher body mass (high larval density) at 50 days post hatch (dph) when fed zooplankton rather than enriched rotifers. A short period (22-36 dph) of dietary change affected larval growth positively if changed from enriched rotifers to natural zooplankton and negatively if prey type changed vice versa. Overall survival did not differ between the two larval groups at low larval density, but at high density the rotifer group had a higher overall survival (10.8% v. 8.9%). Long-term growth was affected significantly by larval diet in favour of the zooplankton diet; juveniles reached a 23% higher mass in a 12 week growth period. No difference in growth performance was found between juveniles fed natural zooplankton during the larval period for 36, 22 or 14 days, but all these juveniles performed significantly better compared with the rotifer-fed group. These findings suggest that optimal diet during a short period in the larval period can result in improved growth in both the larval and juvenile period. Improved rotifer quality may, therefore, hold a large potential for growth improvement in this species.