Morphological development in the first life phase of Adriatic sturgeon Acipenser naccarii under controlled conditions.

Early development of the Adriatic sturgeon Acipenser naccarii from its free embryo after hatching (stage 36), until late embryo stage, when the transition to exogenous feeding starts (stage 45) is described. Special emphasis is given to morphological development and description of the different structures that are formed at each life stage. After hatching, free embryos still present embryonic characteristics, little pigmentation and an ovoid yolk sac. The mouth begins to open on the second day post hatch (dph) and is fully open at 3 dph. The head begins to separate from the body at 4 dph and straightens at 6 dph. The first fins to appear are the pectoral fins on the yolk sac and an embryological fin fold that extends from behind the head to the posterior part of the yolk sac. All other fins will develop from this fold. At 7 dph the caudal fin begins to take a heterocercal form and dorsal scutes are observed. This study provides information that will assist aquaculturists by establishing a reference for the normal development of A. naccarii, which may be useful for evaluating the suitability and quality of fish produced for restocking.

Tissue-specific daily variation in the oxidative status of sturgeon (Acipenser naccarii) and rainbow trout (Oncorhynchus mykiss): a comparative study.

The oxidative status is associated with animal lifespan, metabolism, activity and circadian rhythms. The objective of this work is to study the time course of the oxidative status over a daily cycle in the plasma, liver and brain, and the changes in the plasma cortisol levels of sturgeon and trout. The knowledge of daily oxidative status will provide a better understanding of the trout and sturgeon physiology and adequate maintenance and food supply of farmed fish in relation to photoperiod. Superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione transferase, DT-diaphorase activities, lipid peroxidation and cortisol were measured. Our results showed that the antioxidative enzyme activities and lipid peroxidation in the liver of trout and sturgeon changed through the day, with increased levels in lipid peroxidation of liver in the dark period for sturgeon. This could be related to the different activity time in both species, an issue to be taken into account when designing the guidelines of the maintenance of these species in fish farms. On the contrary, there was not clear influence of the daily rhythms on brain oxidative status. The higher efficiency of the antioxidant defences in the brain of sturgeon, which displays less lipid peroxidation and higher antioxidative activity, could be related to its longer life expectancy. The absence of any apparent daily rhythm in the plasma cortisol levels in sturgeon could indicate a lower susceptibility to stress, and that mechanisms involved in cortisol secretion in chondrosteans could be different from that described for teleosteans.

Study of the olfactory epithelium in the developing sturgeon. Characterization of the crypt cells.

In acipenserids, crypt cells (CCs) have only been observed in juvenile specimens, and it has not been clarified whether they differentiate along with olfactory receptor neurons (ORNs) during the lecithotrophic stage or during later development stages. Furthermore, no detailed optical microscopy (OM) or electron microscopy study on the development of CCs has been published to date. In the present study, we used OM and electron microscopy to follow the development of CCs in Acipenser naccarii from hatching to the establishment of exogenous feeding. Based on these observations, we can affirm that CCs are present from the first few posthatching (PH) days. CCs appear with their nucleus close to the basal lamina of the epithelium and enveloped by supporting cells. In addition, from the beginning of day 2 PH, we observed cells with highly similar characteristics to those of CCs (absence of knob, abundant mitochondria and filamentous material in apical cytoplasm, numerous microtubules, and envelopment by supporting cells) but with cilia still remaining on their noninvaginated apical surface. We conclude that these cells may correspond to immature CCs in which the crypt, the final feature of their morphological differentiation, has not yet formed.

Physiological changes of sturgeon Acipenser naccarii caused by increasing environmental salinity.

The possible repercussions of osmoregulatory processes on some indicators of classical and oxidative stress were examined during gradual acclimation of sturgeons (Acipenser naccarii) to full seawater (35% salinity) and after a period of 20 approximately days at this salinity. Erythrocyte constants and levels of cortisol, protein and glucose in the plasma were determined. In addition, plasma osmolality and muscle-hydration values, as well as liver and heart protein, were determined. Catalase, glutathione peroxidase and superoxide dismutase activities and lipidperoxidation levels were measured in blood (plasma and red blood cells) and tissue (liver and heart). A number of physiological responses, such as disturbance in body fluid, activation of osmoregulatory mechanisms, augmented antioxidant defences in blood and alteration of energy metabolites, were detected with increasing environmental salinity. After 20 days at 35% salinity, plasma osmolality, erythrocyte constants and muscle water content all returned to values usual for low environmental salinity, indicating that osmoregulatory processes have achieved their objective. However, cortisol values, antioxidant enzyme activities in the blood (plasma and red blood cells), lipid peroxidation in plasma, and hepatic proteins did not return to initial values, showing that osmoregulatory processes cause major physiological changes in the fish.