M. Albentosa

Evaluation of live microalgal diets for the seed culture of Ruditapes decussatus using physiological and biochemical parameters.

Abstract The nutritional quality of several microalgal diets used in the seed culture of the little-neck clam, Ruditapes decussatus , was evaluated in the present study. The live diets tested were Isochrysis galbana , clone T-ISO, Tetraselmis suecica and Phaeodactylum tricornutum . Criteria used in the evaluation of the diets were acceptability, digestibility, growth and biochemical composition. The highest growth rate was registered in the seed fed the T. suecica diet, followed by the seed fed I. galbana , while the lowest one was obtained in the seed fed P. tricornutum . Food ingestion rates were higher in the seed fed Tetraselmis . This fact would partly explain the higher growth observed with this diet. The limited nutritional value of Phaeodactylum could be related to the low digestibility of its cell wall, the degree of acceptability of this diet being similar to or even higher than that of the other two. The low protein content of Tetraselmis seems to indicate that R. decussatus shows a low requirement for proteins, which can be spared by carbohydrate, an abundant component in the cells of Tetraselmis . Lipid needs of this bivalve also seem to be rather low.

Comparison of the scope for growth with the growth performance of Ostrea edulis seed reared at different food concentrations in an open-flow system

Oyster (Ostrea edulis L.) seed was reared on five rations of Isochrysis galbana Parke: 10, 30, 100, 200 and 300 cells μl-1, in an open-flow system. Physiological parameters such as clearance, ingestion, absorption and respiration rates were measured, and the scope for growth (SFG) calculated from these parameters was compared with actual growth over 20 d. Actual growth was negligible at 10 cells μl-1 (daily maintenance ration=2.5% organic wt) and maximum (growth rate=13.64 d-1) at 200 cells μl-1 (daily ration=43% organic wt), which also supported the maximum gross and net growth efficiencies (K1=50%, K2=85%). Ingestion rate was directly correlated to cell concentration up to maximum of ∼100 cells μl-1, but further increases failed to support higher ingestions. Absorption efficiency decreased with increasing algal concentration from 95% down to 60%. Due to the costs of growth, respiration rate significantly increased when food was added above maintenance levels; however, metabolic costs associated with feeding activity were undetectable. The scope for growth calculated from these physiological parameters agreed with the long-term growth performance, validating the physiological energetics method as a valuable tool for predicting long-term growth performance under constant environmental conditions.

Fatty Acid Composition of Ruditapes decussatus Spat Fed on Different Microalgae Diets

The fatty acid composition of the Ruditapes decussatus spat fed on three different microalgal diets during 4 weeks was determined. The fatty acid pattern of each diet was also analysed. The diets used were Isochrysis galbana, clone T-ISO, Tetraselmis suecica, and Phaeodactylum tricornutum. The fatty acid composition of the spat was usually well correlated with that of the diet supplied. Major differences among spat cultures were found in 14:0, 16:0, 16:1n-9, 16:1n-7, 18:1n-9, 18:2n-6, 18:3n-3, 18:4n-3, 20:5n-3, 22:5n-6 and 22:6n-3 fatty acids. These differences were correlated with the particular fatty acid content of each diet supplied. It has been shown that R. decussatus spat have a very low capacity to elongate and desaturate linolenic acid to n-3 PUFA, so when 20:5n-3 or 22:6n-3 were not present in the diet, they were also absent, at least in measurable amounts, in the clams. The absence of any of the “essential” fatty acids, 20:5n-3 in T-ISO or 22:6n-3 in Tetraselmis, did not limit spat growth, so their role as “essential” fatty acids might be a matter for discussion. Finally, the nutritive value of each diet was discussed in terms of its fatty acid composition.

Lipid profile and growth of the clam spat, Ruditapes decussatus (L), fed with microalgal diets and cornstarch

Abstract The influence of the lipid composition of microalgal diets and cornstarch on the lipid classes and fatty acids of Ruditapes decussatus spat was studied. These aspects of the nutritional value of the diets are discussed in relation to the growth of the spat. Cornstarch is rich in carbohydrate, but is deficient in protein and lipids. The microalgal cells contains lipid as well as protein and carbohydrate. Tahitian Isochrysis cells contain phospholipids and triacylglycerols as majority lipids, whereas in the cornstarch particles the more abundant lipids are free fatty acids and phospholipids.The n-3 fatty acids were the most abundant acids in the microalgae whereas the n-6 fatty acids were in the cornstarch. The n-3 PUFA were not detected in cornstarch. Diets with a lipid composition high in phospholipids and triacylglycerols and in essential fatty acids produce good growth rates in spat of R. decussatus. However these elements alone are not sufficient to explain the quality of the diet for R. decussatus. In fact, the lipid content of the diet affects growth, but does not explain it totally and it is the carbohydrates content that explains the differences in growth found when we use diets with the same composition in lipids.

Short-term and long-term alterations in the energy budget of young oyster Ostrea edulis L. in response to temperature change

Young post-metamorphic oysters, Ostrea edulis L., previously reared at 20 °C, were exposed to 14 °C (cold treatment), 20 °C (control) and 26 °C (warm treatment) for 3 wk. Algal (Isochrysis galbana Parke) ingestion rate (IR), absorption efficiency (AE), oxygen consumption (ifVo2) and ammonia excretion (VNH4) were measured at the beginning, halfway and at the end of the experimental period. These rates were integrated in the energy budget and the net energy gain available for biomass increase, or scope for growth (SFG), was calculated. All the physiological parameters, including AE, were significantly reduced in oysters acutely exposed to the cold treatment. However, following prolonged cold exposure an increase in IR and a slight decrease in Vo2 allowed compensation of the SFG, which in the long-term achieved similar levels to control. After acute exposure to the warm treatment, oysters showed slightly enhanced IR and VNH4 but no major changes in the other physiological parameters, which yielded a slightly increased SFG. In the long-term, IR markedly increased in warm acclimated oysters which, coupled with sustained metabolic costs, allowed an almost three times increase in the SFG. Different adaptive strategies of acclimation described for bivalves are discussed, under the common aim of SFG maximization following long-term exposure to a temperature change; and peculiarities of fast-growing juveniles are evidenced. It is concluded that juvenile oysters are able to respond in the long-term to either a decrease or increase of temperature, regulating the physiological rates integrated in the energy balance in a manner that renders an overall improvement in the net energy available for growth.

Influence of food concentration on energy balance and growth performance of Venerupis pullastra seed reared in an open-flow system

Abstract Seed of the clam Venerupis pullastra were reared with five different rations of Isochrysis galbana: 15, 30, 100, 200 and 300 cells μl−1, in an open-flow system. Physiological parameters such as clearance, ingestion and absorption rates were recorded, and energy balances calculated from these parameters were compared with the long-term growth performance of the seed. High food concentrations inhibited clearance rate but ingestion could not be regulated, being higher with higher food levels. Absorption efficiency decreased moderately at high I. galbana concentrations. Nevertheless, absorption rate was directly correlated with ingesta. Estimated metabolic rate was at a routine level for medium and high food rations and markedly lower at poor food rations. Growth performance was insignificant at 15 cells μl−1 (daily maintenance ration = 2% organic weight), optimal at 100 cells μl−1 (K1 = 46%) and maximal at 300 cells μl−1 (growth rate = 11.9 day−1), in agreement with the physiological energetics measurements. Growth rates of V. pullastra seed were similar to those reported for other species, such as Ruditapes philippinarum, regarded as a fast growing member of the Veneridae.

Effect of microalgal and inert (cornmeal and cornstarch) diets on growth performance and biochemical composition of Ruditapes decussatus seed

Research was carried out into the effect of phytoplankton, cornmeal and cornstarch diets on growth and biochemical composition of the seed of the little-neck clam, Ruditapes decussatus. The seed of R. decussatus, fed on daily rations of Isochrysis galbana (organic weight) of 0.5 and 1% of live weight of the seed, showed an improvement in growth rate when cornstarch, which is 99% carbohydrate, was added to these diets. Thus in the case of a daily ration of 0.5%, daily growth rates increased by between 33.5 and 32.3%, depending on whether we are referring to organic weight, dry weight or live weight, when 1.5% cornstarch was added. In the case of a ration of 1% I. galbana, the addition of another 1% cornstarch lead to an improvement in daily growth rates, depending on the different weight class in question, of between 14.1 and 15.5%. When compared to a daily ration consisting of 2% phytoplankton, which was considered to be the optimal ration for growth in the seed of these clams, the replacement of half the quantity of I. galbana by a quantity of cornstarch of equivalent weight gave a growth rate in terms of organic weight of 87.9% that of the phytoplankton diet, while the rates for dry weight and live weight were 89.6 and 87.9%, respectively. These results improved noticeably when cornmeal, consisting of 10% protein and 90% carbohydrate, was used instead of cornstarch. In the case of a 2% phytoplankton diet, if we substituted an equivalent quantity of cornmeal for 50% of the phytoplankton, the growth rate in organic matter was the same (99.0%) as those for the diet consisting of phytoplankton alone, while growth rates in dry weight and live weight were 6.2 and 5.9% higher, respectively, than those of the phytoplankton diet. It would therefore appear that cornmeal (and to a lesser extent cornstarch) can be successfully used as a partial substitute for phytoplankton in diets for the seed of R. decussatus and its use in hatcheries and nurseries devoted to the culture of this species would lead to a considerable reduction of production costs.

Determination of optimal thermal conditions for growth of clam (Venerupis pullastra) seed

Abstract The energy budget of Venerupis pullastra clam seed (3 mm) fed the microalga, Isochrysis galbana T-ISO, was calculated after acclimation at 10, 15, 20 and 25°C. Physiological measurements included ingestion rate, absorption efficiency, oxygen consumption and ammonia excretion. The effect of temperature on these rates was described. Ingestion rate was directly related to temperature up to a maximum at 20°C. Further temperature increase caused a slight decrease in ingestion. Absorption efficiency was not significantly influenced by the temperature, although maximum mean values were also found at 20°C. Both respiration and ammonia excretion rates were directly related to temperature over the whole experimental range, reaching their maxima at 25°C. For all the physiological rates measured the higher slopes in the rate/temperature lines occurred in the medium range of temperatures (15–20°C). The scope for growth (SFG) was positive at all temperatures and maximum at 20°C, chiefly as a consequence of the enhanced ingestion rate which offset the concomitant elevation in metabolic rates. Both gross and net growth efficiencies are also expected to be maximum at 20°C, which is, therefore, the thermal optimum for this species under the experimental conditions applied in our study. An acclimation strategy for this low-shore species within the range of thermal variation in its natural environment (10–20°C), maximizing SFG at high temperatures by enhancing ingestion rate, despite increased metabolic costs, is proposed.

Growth performance and biochemical composition of Ruditapes decussatus (L.) spat fed on microalgal and wheatgerm flour diets

Trials were carried out for different growth diets, consisting wholly or partially of wheatgerm flour, for the spat culture of the little-neck clam, Ruditapes decussatus (L.). The following diets were tested: diet A, consisting of 100% of the daily food ration of the microalga Isochrysis galbana, clone T-ISO; diet B, consisting of 50% microalgae and 50% wheatgerm; diet C, consisting of 25% microalgae and 75% wheatgerm; and diet D, consisting of 100% wheatgerm. Diet A was taken as the reference diet and two control diets were added: suboptimal algal diet B, consisting of 50% of the daily ration of microalgae, and suboptimal algal diet C, consisting of 25% microalgae. Spat growth was determined by live weight, dry weight, organic content and length. Biochemical analyses of the diets and the spat were carried out at the beginning and the end of the 35-day experimental period. The growth achieved when 50% of the daily ration of microalgae was replaced by wheatgerm was similar to that obtained with control diet A, consisting of 100% microalgae. As regards organic matter, the growth of the spat fed on this diet, diet B, was double that shown by the spat fed on suboptimal algal diet B. When 75% of the microalgae were replaced by wheatgerm the growth rates decreased, being only equivalent to 60% of those for reference diet A. Nevertheless, the percentage of organic matter of this spat, indicative of the index of condition, was comparable to that of the spat fed on the reference diet. The total replacement of microalgae by wheatgerm produced a considerable decrease in spat growth, 20% of that obtained with reference diet A. The percentage of organic matter in the spat fed on the extreme diets, diet D and suboptimal diets B and C, was observed to be significantly less than that found in the spat fed on the other diets. Another characteristic of the diets tested was a decrease in protein and lipid content, together with an increase in that of carbohydrates, which corresponded to the extent to which microalgae were replaced by wheatgerm. The biochemical composition of the spat reflects a limitation in the lipid content of diets C and D, reflected in a lower lipid growth rate in the spat compared to that of other body matter.

Fatty acid composition of Venerupis pullastra spat fed on different microalgae diets

Abstract Venerupis pullastra spat were fed for 4 weeks on diets consisting of two species of algae which were supplied in single or mixed diets. The microalgal species tested were hochrysis aff. galbana T-ISO and Tetraselmis suecica . The fatty acid pattern of the spat was basically dependent on the diet supplied. Major differences between spat cultures were detected on 14:0, 16:1n—7, 18:0, 18:1n—9, 18:3n-3, 18:4n—3, 20:5n—3 and 22:6n—3 fatty acids. These differences were correlated to those fatty acid contents in the diets supplied, with the exception of the 18:4n —3 fatty acid. This acid was not detected in the Tetraselmis diet but appeared, however, in the spat fed on this microalga. This fatty acid could be obtained from linolenic acid which was present in the Tetraselmis lipids in a high proportion. Special attention was given to the essential fatty acids, 20:5n — 3 and 22:6n — 3. While I. galbana T-ISO cells contain both fatty acids, although 20:5n — 3 in a very low proportion, T. suecica is deficient in 22:6n — 3. Similarly, the T. suecica fed spat is also deficient in 22:6n — 3. Spat fed on the mixed diet shows a fatty acid profile halfway between the two algal species. The absence of 22:6n — 3 in Tetraselmis cells may explain the lower growth rate obtained with this diet.