Evaluation of microalgal diets for the intensive cultivation of the tropical calanoid copepod,Parvocalanus crassirostris

As their natural prey, copepods are considered the ideal diets for hatchery culture of fish larvae. However, intensive cultivation of copepods has proven difficult and low culture productivity is the norm, which severely limits their use in aquaculture. This study investigated the effects of algal diets on a range of productivity‐related parameters, including egg production, hatching success, naupliar and copepodite survival, post‐embryonic development time, population growth and sex ratio of a small‐sized tropical copepod, Parvocalanus crassirostris, which has been identified as a high potential species for aquaculture. The diets tested included three live algal diets: Isochrysis sp. (T‐Iso), Pavlova 50 (Pav) and the diatom Chaetoceros muelleri (Cht); two algal paste diets: Isochrysis sp. (P‐Iso) and Thalassiosira weissflogii (P‐TW), as well as four mixed algae treatments composed of three binary algae diets (T‐Iso + Pav, T‐Iso + Cht and Pav + Cht) and a tri‐algal diet (T‐Iso + Pav + Cht). All parameters examined except sex ratio were significantly affected by the diets. The binary algal diet T‐Iso + Cht produced significant higher total egg production over female lifespan (121.0 ± 5.9 eggs) than all other treatments (P < 0.05). Survival during naupliar and copepodite stage was significantly superior when P. crassirostris were fed either the mixed diet of T‐Iso + Cht or the monoalgal diets of Cht or T‐Iso (P < 0.05) than other diets. These three treatments also had the fastest time of development to adults (ranging from 6.2 to 6.7 days). With an initial 100 adults, the T‐Iso + Cht treatment produced the highest population growth over a 15‐day cultivation period, which was significantly higher than other treatments (P < 0.001). In contrast, the algal paste treatments, including (P‐Iso) produced overall the worst results for various parameters examined. However, the sex ratio of P. crassirostris was not significantly affected by diets and was always heavily skewed towards females (>84% were females) across all treatments. Based on the results of this study, T‐Iso + Cht is recommended for intensive cultivation of P. crassirostris.     

The effects of algal diets on population growth and egg hatching success of the tropical calanoid copepod, Acartia sinjiensis

As natural diets of fish larvae, a number of calanoid copepod species are being investigated for use as live prey in aquaculture hatcheries. One of these, the tropical calanoid copepod, Acartia sinjiensis, has good potential as a live feed for tropical reef fish larvae. However, the rearing techniques for A. sinjiensis require further development to improve productivity. This study was carried out to investigate the population growth and egg hatching success of A. sinjiensis when fed a range of mono-and binary algal diets, including algae in the form of frozen paste.For the population growth experiment, the final A. sinjiensis population, including eggs, nauplii, copepodites and adults, was determined after feeding eight algal diets (two frozen algae, four live monoalgal and two live binary algal diets) for 8 days at temperature 28 ± 1 °C; salinity 34 ± 1 psu and photoperiod 12 L:12 D. Five replicates, with an initial 12 adult A. sinjiensis per replicate, were set up for each treatment. In a separate experiment, effects of diets on egg hatching success were examined after 48 h incubation of eggs produced by A. sinjiensis fed the same eight diets.The results showed that diet significantly affected both population growth and hatching success of A. sinjiensis. Of the diets tested, the binary algal diets were more successful than monoalgal diets, while the frozen algae had little dietary value. The highest population growth was recorded on A. sinjiensis fed a binary diet of Tetraselmis chuii and the Tahitian strain of Isochrysis sp. (T-ISO) (final population: 1091 ± 80), which was significantly higher (P < 0.001) than all other diets tested except for the other binary diet of Nannochloropsis sp. and T-ISO (final population: 897 ± 123). Diet also had a significant effect (P < 0.001) on egg hatching rate, though the highest hatch rate was recorded with eggs produced by A. sinjiensis fed binary diet Nannochloropsis sp. and T-ISO (88.1 ± 2.1%), this was not significantly different from that of eggs produced by A. sinjiensis fed either T-ISO alone (88.0 ± 1.7%) or the binary algal diet of T. chuii and T-ISO (76.4 ± 7.1%). The results of this study suggest that among the diets tested, a combination of live T. chuii and T-ISO was the best for the culture of A. sinjiensis.     

Improving the fitness of Holothuria arguinensis larvae through different microalgae diets

Development and design of adequate feeding protocols on sea cucumber larvae are necessary for improvements on larvae growth, survival and production of competent juveniles. This work assessed the Holothuria arguinensis larvae growth and survival, fed with three different single microalgae diets of Chaetoceros calcitrans, Isochrysis galbana and Tetraselmis chui, and two microalgae diets based on a combination of C. calcitrans and T. chuii (C:T; 1:1) and C. calcitrans, T. chuii and I. galbana (C:T:I; 1:1:1) during 2 months. Holothuria arguinensis larvae fed with T:C:I, showed higher survival and larger larval and stomach sizes than the ones fed with the other diets. Comparing the results obtained from the single diets, H. arguinensis larvae fed with I. galbana grew and survived better during the first 5 days. However, higher growth was obtained on the larvae fed with C. calcitrans from day 5 to day 12; since this day, larvae fed with T. chuii showed the largest size. These results could be related to the different microalgae size and morphology, in addition to the nutritional value of the different microalgae used. However, no competent larvae that metamorphosed into doliolaria were obtained during this experiment. The tanks used were transparent, which could be causing light stress to the larvae, since competent larvae were obtained in opaque production tanks in our aquaculture installations during the same time period. The combined diet of C. calcitrans, T. chuii and I. galbana (C:T:I) could improve the growth and larvae competency of H. arguinensis.     

Comparative growth and survival of spat of the Caribbean pearl oyster,Pinctada imbricata cultivated indoor with microalgae diets and outdoor with natural diet

We report the results of survival and growth in size and dry mass of spat of the Caribbean pearl oyster Pinctada imbricata cultivated under outdoor (field culture) and indoor (Laboratory) conditions. Field group fed on environmental seston. Laboratory groups were fed with mono, binary and ternary mixtures of three cultivated algae: Isochrysis galbana (Ig), Tetraselmis chuii (Ig) and the Chaetoceros sp. (Ch‐A, isolated from north‐eastern Venezuela). After 30 days of trial, fatty acid profiles of spat were determined along with growth in length and height shell, adductor muscle and soft tissue dry mass. During the field grow‐out phase (field culture), samplings were performed at days 1, 15 and 30 to measure environmental variables of phytoplankton biomass (chlorophyll a), dissolved oxygen, seston, temperature and salinity. A significant increase in size and soft tissue mass occurred in spat fed the diets including the tropical diatom (Chaetoceros sp.). In contrast, monoalgal diets of Tc and Ig yielded no significant differences in size and mass of spat, compared with the field culture. These results suggest that nutritional requirements of cultivated spat for specific fatty acids of physiological importance for marine bivalves, such as: 16:0, 16:1n‐7, 18:2n‐6, 20:4n‐6, 18:3n‐3 and 20:5n‐3, were satisfied from microalgal diets with Ch‐A, alone or in combination, compared with spat fed from the field culture.     

Diet trials on tehuelche scallop Aequipecten tehuelchus (d''Orb) larvae

Laboratory spawned one week old veliger larvaeof the tehuelche scallop, Aequipectentehuelchus (D'Orb., 1846), were reared topedivelger stage under three different dietaryregimes in order to determine the best algalcombination under standard hatchery conditions.Veligers were cultured at mean densities of 2.7larvae/ml. Larval growth and survival wereassessed on larvae fed the following dietarytreatments: (1) Isochrysis galbana(T-Iso)+ Chaetoceros calcitrans, (2)Pavlova lutheri + C calcitrans, and (3)P. lutheri + I. galbana T-Iso +Ch. calcitrans. The highest growth rateswere detected on larvae fed diets includingP. lutheri.     

Evaluation of the formulated diet MySpat for feeding hatchery‐reared spat of the green‐lipped mussel,Perna canaliculus (Gmelin, 1791)

As with most bivalves, a high cost component of hatchery and nursery culture of the green‐lipped mussel (Perna canaliculus) is the raising of live micro‐algae feeds. To remedy this, artificial feeds have been developed, however, these have had mixed success for this species. In this experiment, we tested the formulated diet MySpat (sourced from INVE Aquaculture) on P. canaliculus spat of approximately 1 mm in size. Performance measures under study were mussel spat growth and survivorship after 21 days feeding on varying proportions of MySpat. The experimental diets tested, consisted of a mix of T‐Isochrysis galbana, Pavlova lutheri and Tetraselmis suecica micro‐algae that were replaced with increasing proportions of MySpat, i.e. 25%, 50%, 67%, 75%, 90% and 100% MySpat replacement. Our results revealed no significant increase in spat mortality with increasing MySpat diet levels, and growth was equivalent to the micro‐algae only dietary control in all diets except the 90% and 100% MySpat replacement diets. Such results highlight the role MySpat could have for P. canaliculus hatchery operations, particularly with regard to reducing the costs of raising micro‐algae when producing seed for industry. A greater understanding of the particle selection process of this species would be beneficial for future studies seeking to employ artificial diets.     

The effect of several microalgae isolated from East China Sea on growth and survival rate of postset juveniles of razor clam,Sinonovacula constricta (Lamarck, 1818)

Four species of microalgae (Thalassiosira weissflogii, Thalassiosira pseudonana, Nannochloropsis sp. and an unidentified species) were isolated from natural seawater of East China Sea. By studying the effect on growth and survival rates of two sizes of postset juveniles of razor clam, Sinonovacula constricta (Lamarck, 1818) (shell length 0.37 ± 0.05 mm and 1.07 ± 0.08 mm, respectively), the food value of these microalgae and four other commonly used microalgal species in China (Chaetoceros calcitrans, Isochrysis galbana, Platymonas subcordiformis and Nannochloropsis oculata) in single and two algal species diets were evaluated and compared. For smaller juvenile, when used as a monospecies diet, C. calcitrans and I. galbana supported the greatest shell growth and the highest survival rate, and P. subcordiformis, N. oculata and T. weissflogii produced the smallest shell growth and the lowest survival rate. Meanwhile, for the larger juvenile, single‐species algal diet had the greatest and weakest food value on T. weissflogii and N. oculata, respectively. Full‐mixed algal diets exhibited the strongest food value and most of the two species diets supported more food value than corresponding individual single microalgae diet. Moreover, shell growths and the survival rates of larger juvenile fed most of the two species diets were lower than fed single species of T. weissflogii.     

Growth,settlement and survival of Dicathais orbita (Neogastropoda,Mollusca) larvae in response to temperature,diet and settlement cues

The southern Australian whelk, Dicathais orbita, is a potential candidate for aquaculture, as both seafood and for bioactive compound production. Larval rearing experiments to determine the effects of temperature and diet on the growth and survival of D. orbita larvae under laboratory conditions comprised five different unicellular algal diets of two brown algal species; Isochysis galbana and Chaetoceros muelleri, two green algae; Tetraselmis seucica and Nannochloropsis oculata, and a mixture of all four strains for larvae maintained at 16 and 22°C. Absolute growth, specific growth rate (SGR) and survival were determined regularly. Larvae reared at 22°C on a mixed diet, or brown algae, performed significantly better than those reared on green algal diets alone. Preliminary trials with settlement cues were undertaken on different aged larvae to determine when larvae become competent. An array of natural cues (carrion, Xenostrobus pulex, adult mucus and Ulvella lens), as well as concentrations of KCl was tested. KCl(concentration of 20 mM) induced the greatest settlement, however, no larvae metamorphosed under the conditions provided. This study confirms long‐lived planktotrophic larval development for Dicathais orbita with higher development rates at the higher water temperatures. Further studies will optimize culture conditions and cues for settlement and metamorphosis.     

Roles of microalgae on total egg production over female lifespan and egg incubation time,naupliar and copepodite survival,sex ratio and female life expectancy of the copepod Bestiolina similis

We examined the effects of 10 microalgal diets on a range of productivity‐related parameters of Bestiolina similis. The diets tested included four monoalgal diets: Tahitian strain Isochrysis sp. (T‐Iso), Pavlova salina (Pav), Tetraselmis chuii (Tet) and the diatom Chaetoceros muelleri (Chaet), five binary diets: Tet+Pav, T‐Iso+Tet, T‐Iso+Pav, Chaet+Tet and Chaet+Pav and a tri‐algal diet: T‐Iso+Tet+Pav. Except for sex ratio, microalgal diets significantly affected all parameters examined (P<0.05). The shortest egg incubation time was found for the tri‐algal diet treatment (1.91±0.04 days) while the longest (2.41±0.09 days) was from the monoalgal diet Tet. Survival at the naupliar stage ranged from the highest of 86.3±1.0% for the tri‐algal diet to a complete mortality for the Tet diet. Naupliar survival was consistently higher than that of copepodite stages for all diets examined and ranged from 86.3±1.0% for the tri‐algal diet to a complete mortality for the Tet diet. Copepodite survival was the highest for the T‐Iso treatment (69.0±4.3%) while Chaet+Tet produced the lowest survival (8.8±1.2%). Sex ratio of B. similis was strongly skewed towards females. Adult female life expectancy was highly dependent on diet. The shortest lifespan (3.1±0.3 days) of the Tet treatment was only about half of that of Pav (6.3±0.6 days) and the tri‐algal diet (5.9±0.4 days). Daily egg production during female lifespan was generally lower on the first day, but peaked over the subsequent days before decreasing towards the end of their lifespan. The highest total egg output over female lifespan was produced by the tri‐algal diet (156.0±11.5 eggs female^?1), while the lowest output came from the diet Tet (20.7±2.8 eggs female^?1).     

Effect of different dietary microalgae combinations on growth and survival of black‐lip pearl oyster (Pinctada margaritifera) larvae and the feasibility of replacing microalgae with a dietary lipid emulsion

A 10‐day experiment was performed to examine different mono, binary and ternary dietary combinations on survival and growth of D‐shaped and umbone black‐lip pearl oyster, Pinctada margaritifera, larvae. The three tropical microalgae species were the flagellate Isochrysis galbana clone T. Iso (CS‐177) and diatoms Chaetoceros calcitrans (CS‐178) and Chaetoceros muelleri (CS‐176) which were fed to D‐shaped and umbone larvae at a density of 7000 and 14 000 cells mL^?1, respectively. A second experiment was performed to investigate the feasibility of replacing T. Iso with a lipid emulsion for both D‐shaped and umbone larvae for 10 and 12 days, respectively. The treatments included only T. Iso, unfed and lipid emulsion to substitute T. Iso at levels of 10% (LIP10), 30% (LIP30) and 100% (LIP100). In the first experiment, results showed that a monospecific diet of T. Iso led to significantly higher (P < 0.05) survival and growth of D‐shaped larvae than all the other treatments. Meanwhile, D‐shaped larval survival was significantly lower when only fed C. calcitrans as well as growth for those fed C. calcitrans or in combination with C. muelleri. However, for umbone larvae, survival and growth were significantly higher when fed a binary combination of T. Iso and C. muelleri or the ternary combination of T. Iso, C. muelleri and C. calcitrans compared with all other treatments. For the second experiment, results showed that with increasing lipid emulsion replacement, survival of both D‐shaped and umbone larvae significantly decreased (P < 0.05); however, the LIP100 treatment was not significantly different (P > 0.05) from the unfed treatment. For D‐shaped larvae, no significant growth difference was detected (P > 0.05) between the T. Iso and LIP10 fed treatments while for umbone larvae, the T. Iso, LIP10 and LIP30 were not significantly different (P > 005). These results indicate that microalgae combinations appear more necessary for later staged P. margaritifera larvae. In addition, the use of a lipid emulsion appeared to provide some nutrition to the larvae, although more research should be conducted to improve the use of such replacements.     

Effects of single and combined microalgae on larval growth, development and survival of the commercial sea cucumber Holothuria spinifera Theel

The results of the study on the suitable algal feed for the mass rearing of holothurian larvae through hatchery system are presented. Auricularia larvae, after 48 h of fertilization, obtained from induced spawning of Holothuria spinifera, were fed with different algae Isochrysis galbana, Nanochloropsis salina, Pavlova lutheri, Tetraselmis chuii and Chaetoceros calcitrans as well as I. galbana+C. calcitrans to ascertain the effect of single and combined microalgal diet. The rate of feeding was 2 × 10⁴ cells larvae^–1 day^–1 for a period of 9–12 days. The growth rate of 59 μm day⁻¹ with 90% and 43 μm day⁻¹ with 100% occurrence of late auricularia in the larvae fed with C. calcitrans alone and I. galbana+C. calcitrans, respectively, indicated that C.calcitrans itself or in combination with I. galbana is the effective feed for the larvae of H. spinifera.     

Diet trials on tehuelche scallop Aequipecten tehuelchus (d'Orb) larvae

Laboratory spawned one week old veliger larvaeof the tehuelche scallop, Aequipectentehuelchus (D'Orb., 1846), were reared topedivelger stage under three different dietaryregimes in order to determine the best algalcombination under standard hatchery conditions.Veligers were cultured at mean densities of 2.7larvae/ml. Larval growth and survival wereassessed on larvae fed the following dietarytreatments: (1) Isochrysis galbana(T-Iso)+ Chaetoceros calcitrans, (2)Pavlova lutheri + C calcitrans, and (3)P. lutheri + I. galbana T-Iso +Ch. calcitrans. The highest growth rateswere detected on larvae fed diets includingP. lutheri.     

Effect of Rhodomonas salina addition to a standard hatchery diet during the early ontogeny of the scallop Pecten maximus

The main objective of this study was to identify algal diets that maximize the survival and growth and alter the biochemical content of Pecten maximus larvae with the aim of improving metamorphosis. We also evaluated the potential of the cryptophyceae Rhodomonas salina as a food source for these larvae. Two flagellates, Isochrysis aff. galbana (T) and Pavlova lutheri (P), and two diatoms, Chaetoceros gracilis (C) or Skeletonema costatum (S), were tested as two ternary diets, namely PTC and PTS. PTC and PTS were compared with diets that also included R. salina (R). The addition of R. salina and the replacement of C. gracilis by S. costatum in the traditional hatchery diet seem to be two interesting alternatives for increasing the productivity of larval scallop culture and improving the metamorphosis rate. With these two diets, larval growth increased and metamorphosis was observed to occur more rapidly. Moreover, our results showed that the addition of R. salina significantly improved the overall condition of the larvae by promoting an increase in organic matter and total lipids. This accumulation of lipids during ontogeny seems to promote larvae to grow and to complete metamorphosis more rapidly than with the other diets. The level of polyunsaturated fatty acids in the algae could also at least partially explain the results obtained, since the PUFA level of C. gracilis was about half those of S. costatum and R. salina.     

Reproductive performance,survival and development of nauplii and copepodites,sex ratio and adult life expectancy of the harpacticoid copepod,Euterpina acutifrons,fed different microalgal diets

A series of laboratory experiments were conducted on the harpacticoid copepod, Euterpina acutifrons, to assess the influence of 10 different microalgal diets (four monoalgal and six mixed algal diets) on several parameters related to its productivity in culture. The four monoalgal diets were the Tahitian strain of Isochrysis sp. (T‐Iso), Pavlova salina (Pav), Tetraselmis chuii (Tet) and the diatom Chaetoceros muelleri (Chaet), the five binary diets were T‐Iso+Tet, Pav+Tet, T‐Iso+Pav, Tet+Chaet and Pav+Chaet, while the tri‐algal diet was T‐Iso+Tet+Pav. All diets were fed to copepods at 1500 μ gC L^?1 and in the case of binary or trialgal diets, carbon concentration was divided equally between the two or three algae offered. Among monoalgal diets, the diatom Chaet was excellent for E. acutifrons. Out of the 10 diets tested, the binary diet Tet+Chaet, which contained the diatom Chaet, was the best for naupliar production of single pair E. acutifrons (19.5±1.7 nauplii female^?1 day^?1), significantly (P<0.05) higher than all other treatments except for the Chaet treatment (P>0.05). Similarly, in the group naupliar production trial (50 adult E. acutifrons per replicate), Tet+Chaet produced a significantly higher number of nauplii (405.8±18.6 nauplii day^?1) than the other treatments (P<0.05). Tet+Chaet further supported the highest naupliar survival (82.0±2.8%) and copepodite survival (89.0±2.8%), while the mono‐algal diet Chaet produced the second highest naupliar (76.7±2.6%) and copepodite survival (83.5±2.6%). In contrast, Pav produced the lowest overall survival at the naupliar stage (30.0±2.9%), significantly lower than all other treatments (P<0.05). While development from newly hatched nauplii to copepodites was not significantly affected by diets, mean development time from nauplius to adult was significantly different among treatments. Mean development time from hatching (naupliar I stage; NI) to the adult stage was the fastest with Tet+Chaet and Chaet (6.8±0.0 days for both treatments), which was significantly faster than that of Pav, T‐Iso Pav+Tet and T‐Iso+Pav+Te treatment (P<0.05). E. acutifrons sex ratio was significantly affected by diets, and always skewed in favour of males. Feeding on Pav resulted in the lowest proportion of females (23.7±1.2%), significantly lower than for six of the other treatments (P<0.05). Adult females had longer average life expectancy than males for all treatments, and were the longest when fed Tet+Chaet (9.5±0.4 days), which was more than twice as long as the shortest lifespan recorded for the Pav treatment (4.2±0.6 days) (P<0.05). In summary, among 10 diets tested, the binary diet Tet+Chaet appeared to support the highest culture productivity of E. acutifrons while the diatom Chaet also performed well as a monoalgal diet.     

Effects of dietary microalgae on fatty acids and digestive enzymes in copepod Cyclopina kasignete,a potential live food for fish larvae

The copepod Cyclopina kasignete is a potential live food in aquaculture and its fatty acid components and digestive enzymes were investigated. Three dry algal products (mixed algae, Melosira sp. and Nannochloropsis oculata) and two fresh microalgae (Tisochrysis lutea and N. oculata) were fed to the copepod for 30 days. The essential fatty acids (EFA) in copepods were altered by feeding different types of dry algae. The copepod fed dry Melosira sp. or fresh T. lutea contained higher eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and arachidonic acid (ARA), protease and trypsin than fed on other algae. The copepod contained a similar fatty acid profile and digestive enzymes by feeding either dry or fresh N. oculata. Between fresh algal species, the copepod fed T. lutea contained higher EPA, DHA and ARA than that fed fresh N. oculata. The amounts of EPA and DHA in copepods were more concentrated than those in the dietary algae, suggesting that the copepod has the ability to accumulate some EFA. This study indicates that dietary algae can modify the nutritional composition and in digestive enzymes copepods, which in turn may be able to transfer suitable nutrients and digestive enzymes to fish larvae in aquaculture.     

Growth and Survival of Juvenile Feather Duster Worms,Sabellastarte spectabilis,Fed Live and Preserved Algae

The use of live algae and preserved algal products was examined as to their utility in supporting growth and survival of the feather duster worm, Sabellastarte spectabilis. Hatchery‐reared 4‐mo‐old worms were provided the same cell densities of live T‐Iso, preserved T‐Iso, live Nannochlropsis sp., and preserved Nannochloropsis sp. over the course of 132 d. A group of worms placed in a water table that received a continuous flow of raw seawater served as controls. Live and preserved T‐Iso resulted in the highest survival (86.7 ± 6.2% and 78.3 ± 16.5%, respectively) compared to all the other treatments. Live T‐Iso fed worms resulted in significantly larger worms than all other treatments with the preserved T‐Iso treatment supporting similar growth to those being fed live Nannochloropsis sp. and exposed to raw seawater. The preserved Nannochloropsis sp. resulted in significantly lower survival and growth when compared to all the other treatments. Fatty acid profiles of the algal diets and worm carcasses obtained during the current investigation suggest that T‐Iso outperformed Nannochloropsis because of its higher energy or fatty acid content.     

Metamorphosis of larvae of Crassostrea virginica fed microencapsulated diets

This paper reports the results of two feeding experiments in which oyster larvae (Crassostrea virginica) were grown to metamorphosis on microencapsulated diets, and provides the first successful case of culturing oyster larvae to metamorphosis on an artificial diet. Five to 25% of the larvae fed microencapsulated diets grew to the “eyed” stage in 22–25 days. About 2–20% of these “eyed” larvae metamorphosed and settled and 25–40% of these settled larvae produced spat (> 0.05 mm). Two concentrations of two microencapsulated diets were tested; results indicated that diet concentration affects larval growth and development.Microcapsules with capsule walls made of a lipid mixture containing ethyl cellulose and stearic acid improved the retention of water-soluble components. Capsules were more stable at low temperature (5°C) than at higher temperatures (22 and 28°C). Inclusion of lipid algal extract in gelatin-acacia capsules promoted better growth of larvae than those not containing the algal extract. This suggests that attractants or phagostimulants could play an important role in microencapsulated diets.     

Growth, survival, quality and digestive enzyme activities of larval shrimp fed microencapsulated, mixed and live diets

An artificial diet for shrimp larvae was microencapsulated with a polysaccharide blend [66% gum arabic, 17% mesquite gum and 17% maltodextrin 10 dextrose equivalent (DE)]. Microencapsulated diet (MD) was fed to mysis alone, as a co‐feed with the microalgae Chaetoceros cerastosporum and Tetraselmis chuii (mixed) and compared with a live diet (control) of C. cerastosporum, T. chuii and Artemia nauplii. No significant differences (P > 0.05) were detected in growth rates, development and quality indexes of larvae fed the three experimental diets. All diets supported survival percentages of >90%. Shrimp larvae fed MD and mixed diets had higher specific trypsin activity and soluble protein content than those fed live diet. Amylase activity decreased in larvae fed the mixed and MD apparently due to the carbohydrate composition of the diet. The results indicate that it is possible to substitute a live diet with a microencapsulated one (with a wall composition made up of a polysaccharide blend) in Litopenaeus vannamei mysis.     

Broodstock conditioning of the Portuguese oyster (Crassostrea angulata,Lamarck, 1819): influence of different diets

The Portuguese oyster Crassostrea angulata shows great potential in oyster farming. The conservation of pure populations of this species is important for production diversification and biodiversity preservation. In this way, the zootechnological development for seed hatchery production is extremely important. Broodstock conditioning is a key step in the process of rearing bivalves in a hatchery. Many factors regulate the reproductive cycle, being food one of the most important ones. To evaluate the effect of different diets on C. angulata reproductive performance, broodstock were conditioned with different food regimes formulated fundamentally by flagellates (Diet 1 – Pavlova lutheri and Isochrysis galbana clone T‐ISO; Diet 2 – P. lutheri, T‐ISO and Skeletonema costatum) and constituted fundamentally by diatoms (Diet 3 – S. costatum and Chaetoceros calcitrans; Diet 4 – P. lutheri, S. costatum and C. calcitrans). During conditioning, samples of oysters were collected to evaluate condition index, gonadal development and biochemical composition. At the end of the conditioning period, oysters were induced to spawn to evaluate reproductive output (fecundity, fertilization rate and D‐larvae development). The diets had an impact on the gametogenesis process, energy storage and reproductive output performance, being the best results those obtained in broodstock fed with the diatoms‐predominant diets. However, those fed with diets majority flagellates had an unsuccessful performance. Holistic approaches incorporating all results in this study reveal and reinforce the idea that the diatom species used presented the nutritional requirements to C. angulata broodstock, being essential in the conditioning phase.     

Microbial environments in marine larviculture:Impacts of algal growth rates on the bacterial load in six microalgae

The impacts of varying algal growth rates on the bacterial load in the cultures were studied for six marine microalgae: Skeletonema costatum ,Chaetoceros mülleri (Bacillariophyceae), Nannochloropsis oculata (Eustigmatophyceae), Isochrysis galbana, Pavlova lutheri (Haptophyceae), and Tetraselmis sp. (Prasinophyceae). Samples were taken in batch cultures during early exponential phase and in stationary phase when the growth rate was below 5% of maximum growth rate (µ_max). Except for C. mülleri and N. oculata, the microalgae were thereafter grown semi-continuously at dilution rates of 20% and 60% of µ_max and samples taken during a period of 10 days.Higher bacterial levels were associated with slow-growing microalgae on a per volume basis. Per algal cell, variations in the bacterial load were more related to species. Relatively high bacterial densities (5.7–16.4 CFU algal cell^–1) with large proportions of opportunistic and haemolytic species were associated with the Bacillariophyceae. For the other species, the bacterial density was 0.2–4.3 CFU algal cell^–1. Bacterial levels were in general lower and not affected to the same extent by algal growth conditions in Tetraselmis sp. and P. lutheri. No or very low levels of presumptive Vibrio spp. were observed, except in semi-continuous cultures of P. lutheri. Cultures of Tetraselmis sp. had low levels of opportunistic bacteria at all growth conditions.