En julio de 1989 y 1990 se hicieron dos cosechas comerciales de Gelidium sesquipedale mediante arranque y corte, con objeto de observar la recuperación, obteniendo datos que sienten las bases biológicas para establecer un plan de gestión del recurso.

Se observa una reducción de la biomasa del 80 % tras la cosecha, no variando la densidad de frondes y reduciéndose la talla media de la poblacion un 48 % por corte y un 31 % por arranque. Los 3 ó 4 meses que siguen a la cosecha son muy importantes en la recuperación de la biomasa, de manera que en octubre ya no existen diferencias significativas entre las medias de las zonas cosechadas y control. En este período, frente a tasas de crecimiento nulas en la zona control, se obtienen valores alrededor de 1.3 %.día−1 en las cosechadas, mientras que entre marzo y julio oscilan alrededor de 0.9 %.día.−1.

La producción es 1.4 veces mayor en las áreas cosechadas (valores alrededor de 1 100 g.m−2.año−1), mientras que las tasas de renovación son 2.5 veces mayores en ellas (6.8 año−1).

Los epífitos prácticamente desaparecen tras la cosecha, pero se recuperan al mes siguiente, no aumentando su biomasa en relación a la de la control.

This study was undertaken in a pond used for natural spawning of pike. Zooplankton and pike larvae were sampled using a horizontal haul net (120 μm or 1 mm mesh size) through the aquatic vegetation. Among the different class sizes of larvae, one cohort was isolated (11.1 mm < L < 46 mm), in which larval pike first fed on small Cyclopoids then switched to Cladocerans until they fed on insect larvae. Length (1.2 mm/day) and weight growth were found to be fast. Between day 8 and day 13 of exogenous feeding there was a marked decrease of reserve lipids of larvae. This decrease coincided with a lower growth and seemed to be ascribable to changes from Cyclopoid (60.4% of ingested prey) to 2 species of Cladoceran (42.4% and 36.4% of ingested prey), in the feeding sequence of larvae. Pike probably found difficulties in capturing Cyclopoid and digesting Cladocerans as their alimentary canal was not completely developed. After day 13, Cladoceran digestibility was good as the S-bend gut was formed, when triacylglycerol content of larvae increased until the experiment ceased. As indicators, of good growth, we detected increasing amounts of phospholipids throughout the whole study. The fatty acid composition of larval triacylglycerols appeared to be very similar to the composition of zooplankton lipids. Dietary fatty acids could have been incorporated whithout modification into triacylglycerols and into phospholipids possibly with limited elongation/desaturation. The results suggest that pike larvae require both (n-3) FA and (n-6) FA.

Dry diets containing varying levels of dried fermented fish silage and soybean meal blend (FS: SBM) as replacement for 25,50 or 75% of fish meal protein were fed to juvenile Oreochromis niloticus (8.2 ± 0.1 g) and Clarias gariepinus (10.8 ± 0.3 g) at 5% body weight per day for 70 days. Diets containing co-dried FS: SBM supported weight gains and growth rates similar to those in the control treatment without significant differences (p > 0.05). Feed conversion, protein efficiency ratio and protein productive values followed a similar trend with growth performance values. Apparent protein digestibility decreased in both fish species with increasing dietary level of co-dried FS: SBM Carcass composition of experimental fish were not affected by the diets and morphological defects were not observed. Results indicate that co-dried FS: SBM can partially replace fish meal protein as well as establish the potential of utilizing waste/undersized tilapias as a protein feedstuff in dry aquaculture diets.

A non-destructive method for determining water, protein, lipid and ash content along with lean body mass (LBM; total body mass – total lipid mass) in live channel catfish was evaluated. This non-invasive technique involved placing the fish within a low-frequency electromagnetic field and measuring the total body electrical conductivity (TOBEC) based on the distinct electrical characteristics of body fat and fat-free tissues. The correlations between TOBEC and whole-body composition were examined using age-1+ channel catfish ranging from 44 to 175 g. Significant linear relationships between TOBEC, body weight, and total length, or combinations of these parameters, and LBM, ash, lipid, protein, and water content were found; r2 values ranged from 0.863 to 0.998. Equations for predicting body composition from TOBEC and morphometric measurements were developed. Analysis of an independent group of fish demonstrated TOBEC equations to be reliable predictors of body composition. This technique should allow successive monitoring of body composition of individual fish at different times and provide additional insight into the body composition dynamics of channel catfish.

The process of sperm penetration into the egg of the European catfish Silurus glanis L. was investigated by scanning and transmission electron microscopy. Unfertilized ovum membrane under the internal micropylar aperture shows a critical depression with undulation and short microvilli corresponding to a specialized sperm entry site structure. Twenty seconds after insemination, the fertilizing spermatozoon fused with the egg at this specialized structure, without formation of an earlier fertilization cone, which had been confirmed in eggs of other fish. A cytoplasmic eminence developed however, immediately under the fused sperm head and then disappeared with time after fertilization to form a circular area around the fused sperm head, which in turn became embedded in the circular area with shortening of the flagellum. The micropyle in the catfish egg consisted of a micropylar vestibule and a canal, the internal micropylar canal being wide enough to permit the penetration of only one spermatozoon.

With the aim of establishing cryopreservation protocols for oyster (Crassostrea gigas) embryos, toxicity of single or combined cryoprotectants to oyster embryos was investigated. In experiments on the toxicity tolerance of oyster embryos, four conventional cryoprotectants, namely, acetamide (A), dimethyl sulfoxide (DMSO), ethylene glycol (EG) and propylene glycol (PG), with concentrations from 1 to 5 M were used to test the toxicity tolerance of oyster embryos at eight different developemental stages. On a molar-equivalent basis, DMSO appeared to be less toxic to PG, EG and acetamide in general. Oyster embryos were tolerant to low concentrations of all cryoprotectants tested in the range from 1 M to 2 M for all developmental stages. Early stage embryos were more vulnerable to high concentration (4 M and 5 M) cryoprotectants tested than late stage embryos. Experiments were subsequently performed to study the combined effects of DMSO and acetamide adding trehalose or glucose in reducing toxicity to 4 hour oyster embryos. The use of trehalose or glucose reduced toxicity of high cryoprotectant concentrations. Survival was higher when DMSO was combined with acetamide than when using DMSO or acetamide alone at high concentration (5 M). By adding trehalose to combined 5 M DMSO and acetamide (total concentration) an average survival rate of 67 ± 7% was obtained in contrast to 8 ± 5% or 2 ± 1% survival when testing with 5 M DMSO or 5 M acetamide, respectively.

The present results come from the campaigns of the international multidisciplinary programme conducted by P. La Violette (Naval Oceans Research and Development Activities, NORDA), the Western Mediterranean Circulation Experiment. The mesoscale instabilities of the Mediterranean circulation induce meanders, gyres and eddies acting on the production potential of living resources. These resources are evidenced here through the cetaceans and other large organisms directly observable in the surface waters of the sea, along the track of the cruise NORDA 706 (May-June 1986), and through the underlying biomasses detected by an echo sounder, 12 kHz fishfinder. Acoustics detection was continuous, set at the same level by day and night for 15 days intenupted only when the ship stopped for hydrological measurements at 87 CTD sampling stations. The pattern of hydrological sampling was designed in order to identify the intermediate water veins in the Algerian Basin. The three sets of field data - daily visual census, continuous echo-sounding and hydrological profiles - were compared and processed in statistical factorial and multiregression analyses. These show that presence of cetaceans coincides with highly concentrated echos; other large organisms observed are distributed at random, without any link with the concentrated echos. It results that cetaceans have the ability to detect acoustically the same biomasses as humans do with a 12 kHz echo-sounder; this is an argument for the "echolocation of the Odontoceta" and "vocalization of the Mysticeta"; up to now, such processes are not accepted by all cetologists. Four examples of echogram are reported here associated with fin whales, sperm whales, pilot whales and dolphins. Dynamical analysis of the Mediterranean circulation before and during the cruise by contemporaneous remote sensing imagery (CZCS and NOAA 9) enables deduction of the dynamic characteristics of the areas where high densities of acoustical detection co-occur with the presence of cetaceans. Such areas are enriched by the intermediate water by a shearing effect against the edge or the bottom of an eddy, i.e. at the contact between two water bodies moving in opposite directions; it can also happen on the edges of two eddies where they become tangential. Thus, four areas of high productivity of living resources (high trophic-chain levels) are evidenced here in the Algerian Basin. One is linked with the frontal process of the Almeria-Oran Front; the three others, not previously described, concern the influx of levantine intermediate water into the Western Mediterranean Basin.

The aquaculture production of all-female triploid (sterile) populations is recognized as being of potential advantage for many species of fish where sexual maturation is not desired. All-female triploids have been produced by inducing triploidy in eggs that had been fertilized with monosex female sperm. However, monosex stocks to produce this type of sperm are currently available only for a limited number of economically important species. To circumvent this problem, an alternative method would be the direct fertilization of tripoid embryos. In Pacific salmon, pressure shocks applied shortly after fertilization have consistently resulted in high yields of tripoids, and feminization by direct estrogen treatment has also been shown to be highly effective if applied shortly after hatching. In this study, coho salmon eggs were made triploid by a pressure shock of 633 kg/cm2 for 4 min, applied 20 min after fertilization and incubation at 10 °C. Some of the resulting embryos were then feminized with estradiol-17β in single 2-hour immersion treatments at 400 μg/liter, administered 1 and 8 days after hatching. Six months later, when the fish were juveniles, analysis of the DNA content of erythrocytes by flow cytometry revealed a 100% induction of triploidy, while histological examination of the gonads showed 82% females, which were completely devoid of oocyte development and thus genetically sterile. These manipulations reduced survival during early stages of development but survival became stable later. Together, these results suggest that the production of sterile fish by direct feminization of induced triploids could be of particular advantage for those species in which all-female stocks are yet not available or difficult to obtain.