Monoalgal Diets Research Articles

Fatty acid contribution of microalgal diets on spat performance of the tropical mangrove oyster Crassostrea rhizophorae, in Mochima Bay, Venezuela

Fatty acids play a fundamental role in the ecology and growth of many invertebrates, such as filter-feeder bivalve. To guarantee adequate nutrition during transfer from the nursery to the natural environment, we studied the survival, growth and fatty acid (FA) profile of Crassostrea rhizophorae oyster spat fed with seven microalgae combinations of Chaetoceros sp. Araya strain (Ch-A), Tisochrysis lutea (Tl) and Tetraselmis chuii (Tc). The diets included three monoalgal diets (Ch-A, Tl and Tc), three binary combinations (Tl+Ch-A, Tl+Tc and Ch-A+Tc) and one ternary mixture (Tc+Ch-A+Tl). Groups of triplicated carboys each containing 21 oyster spat were used to test the experimental diets, while an additional group was deployed directly in the environment as a control. After 36 days, total lipids, FA profiles and biometric parameters of the spat were analyzed.​ The spat were then transferred to the outdoor environment, and cultivated under suspension conditions for 30 additional days. At the end of this period, FA profiles and growth were again determined. Environmental variables were sampled weekly. Highest shell height growth and soft tissues mass were observed in the spat fed with Ch-A in any combination: the mono-algae Ch-A diet, the binary Ch-A+Tc and Ch-A+Tl diets, a tendency that persisted in the outdoor environment. Our results showed lower shell and soft tissues mass growth, and a drop in the levels of certain FAs of the spat after their transfer to the natural environment, such as 14:0, 16:1n-7, 18:1n-9, 18:4n-3 and 20:5n-3 FA. This effect probably reflected a compensation strategy for the scarce availability of food and higher temperatures observed in the natural environment.

Evaluation of suitable micro‐algal diets for intensive culture of the calanoid copepod Acartia bilobata

Copepods are alternative live feed in marine fish hatcheries, and the quality and type of micro-algal diets influence their culture productivity. Three algal species of different groups including prymnesiophyte: Isochrysis galbana (Iso), the diatom: Chaetoceros muelleri (Cht) and eustigmatophyte: Nannochloropsis occulata (Nan) were fed to the calanoid copepod Acartia bilobata. Selected algae were offered as mono-algal diets: T1-Iso, T2-Cht and T3-Nan or as mixed algal diets: T4-Nan + Cht, T5-Nan + Iso, T6-Iso + Cht and T7-Iso + Cht + Nan. Reproductive parameters, egg production, hatching success, nauplii and copepodite survival, development and first maturity, were closely monitored. Results illustrated that I. galbana was the most suitable diet for this copepod species, supporting higher average relative egg production (5631.62 ± 133.49 egg L−1 day−1), hatching success (96.32 ± 1.40%) and superior adult survival (44.44 ± 3.20%). Different algal diets influenced the nauplii and copepodite survival rate. Maximum survival to adults (56.67 ± 3.78%) and shortened development time (5.75 ± 0.12 days) and time to first maturity (4.50 ± 0.12 days) were observed when fed with I. galbana. The groups fed with C. muelleri exhibited lower survival (6.67 ± 0.67%) during development into adults, and the group fed with N. occulata alone or with C. muelleri did not survived till the adults. Amongst seven algal diets tested, I. galbana was found ideal for maximizing culture productivity, and hence recommended for intensive culture of A. bilobata.

Larval calcification and growth of veligers to early pediveliger of the queen conch Strombus gigas in mesocosm and laboratory conditions

The goals of this study were to evaluate growth, development, and calcification process of veligers of Strombus gigas grown in natural conditions in mesocosm versus laboratory conditions. In this study, larvae bred in mesocosm conditions had a good growth rate (33.3±12.40 μm.day−1) when fed with natural phytoplankton in natural flowing seawater versus a lower growth rate of 8.8±5.20 μm.day−1 for larvae reared in laboratory conditions and fed with a monoalgal diet of Nannochloropsis oculata. Physicochemical parameters did not explain the difference on larval growth in both culture systems according to the principal component analysis done. Raman microspectrometry carried out on conch larvae grown in mesocosm and lab conditions allowed us to emphasize the biosynthesis of calcium carbonate species and their structure type evolution (amorphous, aragonite, or calcite structure) as a function of the breeding time by detecting and identifying in the spectra the characteristic Raman bands of CO3 chemical groups and lattice vibrations. This analytical method seems to indicate that crystalline CaCO3 structures are not detected in the recorded spectra on larvae reared in laboratory conditions during the early stages of the shell construction of 1 to 8 days. For this reason, light and current flow have also been considered in the discussion that can help to explain the differences found in this study. Contrarily, the Raman spectra acquired on larvae grown in mesocosms exhibit characteristic bands of aragonite (CO3 double peak at 697–701 cm−1 and lattice vibrations at 170 and 220 cm−1) from the third day of breeding. The best shell growth and shell calcification pointed out in larvae grown in mesocosm compared to laboratory conditions are probably due to the nutrient amounts present in the food available in mesocosm.

Growth performance and nutritional profile of a cyclopoid copepod Oithona similis isolated from Kochi, south west coast of India

A series of experiments of each 25 days were conducted to evaluate the suitability of four microalgal diets for the culture of the tropical cyclopoid copepod Oithona similis. The mono-algal diets were Chaetoceros calcitrans, Isochrysis galbana, Chlorella marina and Nannochloropsis oculata. Present work was carried out in a Completely Randomized Design (CRD) with four treatments and three replicates. After feeding O. similis with the 4 algal diets for 25 days, population density of adults, copepodites, nauplii and egg bearers were determined. Density and population growth rate of all stages were the maximum when fed with C. calcitrans and it was confirmed as an excellent diet for O. similis. Growth performance as indicated by population density and growth rate was significantly (P<0.05) higher for all stages when fed with C. calcitrans compared to the rest of the diets. The biochemical profile of O. similis showed superiority in protein (55.6%), and lipid (33.4%) contents on feeding with C. calcitrans. Since the strain is cultivable with good nutritional profile and high survival rate, it gives an immense scope of high value larval feed for use in marine hatcheries. Based on the current results, it is suggested that among the diets tested, the diatom C.calcitrans was the best for enhanced production of all stages of O. similis in controlled conditions followed by I. galbana

Microalgal diet evaluation in the larval development and substrate selection for settlement in the rock oysterStriostrea prismatica (Gray, 1825)

Monoalgal and bialgal diet were tried in 2 stages of larval development of Striostrea prismatica: phase I from mixotrofic to early umbonated veliger larva and phase II until eyespot larvae. The monoalgal diets in phase I were Tisochrysis lutea, Pavlova lutheri and Nannochloropsis sp. In phase II, Tetraselmis suecica, T. chuii, Chaetoceros gracilis and Ch. muelleri were incorporated. The bialgal diets (combination of P. lutheri + Ch. gracilis in proportions 1:3, 1:1 and 3:1) were chosen according to the results of the monoalgal trials and were evaluated against the classic diet = control (T. lutea + Ch. gracilis). The microalgae size and their fatty acid composition were determined. We recommend the combination T. lutea + Ch. gracilis, initially using T. lutea for mixotrophic larvae (6 days Post Fertilization-PF), then incorporating Ch. gracilis in a ratio of 1:1 until completing phase I (8–10 PF). In phase II, the ratio should change to 1:3 until larvae with eyespot are obtained (18–20 PF). Suggestions were based on the higher demand for DHA in initial larvae and the need for EPA from the early umbonated phase. Finally, as a third experiment, microsubstrates (pieces of shells, sandpaper, polycarbonate and ground rubber) were evaluated to promote the settlement of pediveliger larvae. A settlement of 20% was obtained in pieces of shells of the same species. We consider that the settlement technology has not been optimized; therefore, evaluations directed at the behaviour of the species are recommended.

Effect of Seawater Acidity on the Initial Development of Kumamoto Oyster Larvae Crassostrea sikamea (Amemiya, 1928)

The oceans have absorbed more than 40% of the carbon dioxide (CO2) generated by anthropogenic activities, causing a decrease in the average pH of 0.1 units in seawater since preindustrial times. This phenomenon has been called “ocean acidification.” This change poses serious threats to the cultivation of oysters and especially to larval and spat production, activities carried out in coastal and estuarine areas, where pH levels are currently below the IPCC scenario for the year 2100 of pH = 7.8. The goal of the present work was to experimentally evaluate the effect of simulated acidification (pH 7.39 ± 0.04) on the culture in a short-term trial of Kumamoto oyster larvae Crassostrea sikamea taking the current ocean pH conditions (pH 8.116 ± 0.023) as a reference. The evaluation was carried out in an experimental system with continuous water flow and pH manipulation by CO2 bubbling. Veliger larvae (6-day-old postspawn) were cultured at a density of six larvae mL–1 and fed with a monoalgal diet based on Isochrysis galbana at 30,000 cells mL–1. Mortality (%) and growth (shell length in µm) were evaluated, and damage to larval morphology (determined using scanning electron microscopy) and Ca2+ contents in the shells (%) were quantified by X-ray fluorescence. The results show a high sensitivity of C. sikamea veliger larvae to low pH levels with negative impacts on growth and survival, decreases in the Ca2+ concentrations of the shells, and the presence of morphological anomalies during the prodissoconch I stage, which were observed after the first 24 h of cultivation in experimental conditions and became progressively more evident, especially by the sixth day of culture. Acute exposure to a low pH and a saturation of aragonite (Ωar) <1 caused poor calcification in C. sikamea larvae, causing negative effects on larvae, such as shell lesions during development, smaller larvae, and higher mortality and relation to a control pH.

Separating viscous and thermal effects of temperature on copepod feeding

AbstractBecause seawater temperature is correlated with viscosity, temperature changes may impact small zooplankton through a mechanical pathway, separately from any thermally-induced effects on metabolism. We evaluated both viscous and thermal effects on copepod feeding in experiments where viscosity was manipulated separately from temperature using a non-toxic polymer. Two copepod species, Acartia tonsa and Parvocalanus crassirostris, feeding on two monoalgal diets (a diatom and a dinoflagellate) were compared. At constant temperature, increase in viscosity nearly always reduced feeding; at constant viscosity, changes in temperature had no effect on feeding. The effects of viscosity and temperature were more pronounced for the diatom than the flagellate prey. Overall, reductions in zooplankton feeding at cold temperatures can be explained primarily by the mechanical effect of viscosity. Q10 values for copepod feeding (1.0–7.9), calculated from the present data and from the literature, were generally higher and more variable than Q10 values from the literature for copepod respiration (1.5–3.1) indicating that, at cold temperatures, feeding is more dramatically suppressed than metabolism. We conclude that (i) high viscosity may inhibit copepod feeding, and (ii) this viscous effect on feeding (rather than a thermal effect on metabolism) may influence the cold-temperature bounds of zooplankton populations.

Microalgae diet for juveniles of Spondylus limbatus

The effects of mono- and bi-microalgal diets on shell length, organic tissue, and survival of Spondylus limbatus juveniles were tested in two separate feeding experiments. The first examined nine single species of microalgae: Chaetoceros gracilis, C. muelleri, Isochrysis aff. galbana (T-ISO), Tetraselmis chuii, T. maculata, Pavlova lutheri, Dunaliella salina, Rhodomonas sp., and Nannochloropsis sp. An extra treatment maintaining the juveniles in a long line culture was at Ayangue Bay, Province of Santa Elena, Ecuador. Single diets of P. lutheri, C. muelleri, and C. gracilis showed the best combined growth of survival performance in juveniles, and were therefore selected for the bi-algal diet experiment design with the inclusion of I. galbana T-ISO due to its recommended use in bivalve culture. A second experiment consisted in selecting the best three microalgae species that resulted from the first experiment and combined each other in binary treatments at 1:1 ratio. All bi-algal diets in combination with P. lutheri showed good result in growth (shell and biomass), yield, and survival. However, single P. lutheri mono-algal diet showed equal or better performance index than the other bi-algal combined diets, demonstrating the pertinence in using this microalga as food for S. limbatus juveniles.

Impact of food type on growth, survival and reproduction of the cyclopoid copepod Cyclopina kasignete as a potential live food in aquaculture

This study compared the efficacy of different dietary algae on the growth and reproduction of the cyclopoid copepod Cyclopina kasignete, a potential live food species for fish larvae in aquaculture. The experimental diets for the copepod consisted of three monoalgal diets (Nannochloropsis oculata, Tisochrysis lutea and dry Melosira sp.) and two mixed algae diets (T. lutea + N. oculata, T. lutea + dry Melosira sp.). The experiment was carried out for 30 days, and the population growth, survival and reproductive performance (generation time, hatching rate, life spawning times, daily offspring production, eggs per sac, lifespan and sex ratio) were used to assess the responses of C. kasignete to different food types. Population growth, survival and reproductive capacities of C. kasignete were significantly affected by the mono and binary species of algal diets. The results showed that copepods exhibited superior growth, survival and productivity when fed on fresh T. lutea, dry Melosira sp. and a mixture of both species compared to other dietary treatments. Copepods produced comparable growth, survival and productivity when fed on diatoms (dry Melosira sp.) as a single or in combination with other algae. This study indicates that cyclopoid copepod C. kasignete grow fast and have the potential to serve as a live food for aquaculture. The algae T. lutea, dry Melosira sp. and their combination are appropriate food to sustain the growth and reproduction of this copepods in mass culture as a potential live food in fish hatchery.

Grazing and performance of the copepod Pseudodiaptomus poplesia on a Chinese strain of Aureococcus anophagefferens

Brown tides have recurred in estuary areas globally, but trophic interactions between the causative species Aureococcus anophagefferens and planktonic copepods remain poorly understood. In this study, we investigated performance (ingestion, growth, development and reproduction) of the planktonic copepod, Pseudodiaptomus poplesia, offered either mono-algal or mixed-algal diets containing a Chinese strain of A. anophagefferens. A typical Michaelis-Menten pattern existed between ingestion rate and food level when copepod fed on the monoalgal diet of this species. Nauplii exhibited the highest maximum ingestion rate (Imax) than copepodids and adult females. In addition, Imax value was higher in nauplii feeding on A. anophagefferens than on Skeletonema costatum. When fed mixtures of A. anophagefferens and S. costatum, P. poplesia selected against A. anophagefferens cells, but less strongly at the naupliar stage. Nauplii did not undergo metamorphosis and died at late naupliar stages feeding on A. anophagefferens alone, similar to those under starvation. Furthermore, the presence of A. anophagefferens greatly reduced the reproduction rate of females in mixtures but did not influence the growth rate of copepodids. These results suggest that P. poplesia nauplii may exert grazing pressure on A. anophagefferens population during a brown tide, which, however, may not be persistent because of copepod population decline.

The effect of different dietary microalgae on the fatty acid profile, fecundity and population development of the calanoid copepod Pseudodiaptomus hessei (Copepoda: Calanoida)

We studied the effect of dietary microalgae on the fecundity, population development, and fatty acid profile [with focus on the essential fatty acids docosahexaenoic acid (DHA; 22:6ω3) and eicosapentaenoic acid (EPA; 20:5ω3)] of the calanoid copepod Pseudodiaptomus hessei, a potential live food for finfish larvae in aquaculture. Two mono-algal diets, the Tahitian strain of Isochrysis galbana and Rhodomonas salina, and a 50:50 binary diet of the two were fed to copepods. Wild caught copepods were used as a baseline reference point. Copepods fed I. galbana and the 50:50 binary diet had high DHA:EPA ratios and DHA content relative to those fed R. salina. The EPA content of the copepods was similar for all three diets. Copepods fed R. salina had the highest fecundity relative to those fed I. galbana and the 50:50 binary diet. The largest population was obtained when the copepods were fed I. galbana, which differed from those fed R. salina and the 50:50 binary diet. The results of this study showed that the fatty acid composition of P. hessei can be altered by changing its dietary microalgae, and that the copepod can accumulate fatty acids from its diet, especially DHA and EPA. Diet also affected fecundity and population development of P. hessei, so this species represents a potential live food candidate for marine finfish larvae as its nutritional composition and productivity can be manipulated to suit the needs of marine finfish larvae.

Comparative growth and survival of spat of the Caribbean pearl oyster,Pinctada imbricatacultivated 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.

Early life cycle and effects of microalgal diets on larval development of the spiny rock-scallop, Spondylus limbatus (Sowerby II, 1847)

The Spondylus limbatus fishery in most of the eastern Pacific is restricted due to a decline in natural populations. The aquaculture production of seedlings applying proper larviculture techniques could contribute to the restoration programs of this valuable fishing resource. However, literature of proper culture techniques for S. limbatus is scarce. We describe the embryonic, larval and post-larval development of S. limbatus raised in the laboratory, and the effect of two monoalgal (Chaetoceros gracilis, CG; and Isochrysis galbana, IG) diets and a combination of different cell ratios (3CG:1IG, 1CG:3IG and 1CG:1IG) on growth and survival of S. limbatus larvae. Fertilized eggs had a diameter of 60.2±1.3μm. Swimming D-larvae, with a shell length of 98.0±2.2μm, were obtained within 26h; and pediveligers (185.2±3.9μm) in 12days. At day 16 (>200μm) pediveligers metamorphosed into postlarvae and the dissoconch appeared. After metamorphosis, we did not observe byssus production and post-larvae were capable of remaining free (in plantigrade stage) for 2–3months, with crawling movements until settlement by cementation took place on hard substrates. The post-larval settling behavior is suggested to be characteristic of the genus Spondylus. The algal diet experiment revealed significantly larger larvae (164.0±1.8μm) and faster growth (5.5±0.0μmday−1) with 3CG:1IG treatment, while survival was higher when fed CG alone (18.8±4.3%). The embryogenesis and larval development of S. limbatus are similar to other Pectinidae species. The combination of C. gracilis and I. galbana (3:1) could be used as an appropriate diet for S. limbatus larval culture. Future research will be focused on improving survival of competent S. limbatus larvae by implementing water treatment systems and consequently testing preference substrates that potentially stimulate attachment and cementation on this species.Statement of relevanceThis study presents a complete description of the embryonic and larval development of S. limbatus. Additionally, we determined an appropriate diet (C. gracilis, I. galbana; 3:1) for enhancing larval growth and survival of this commercially and ecologically important species. Finally, we provide unpublished observations about the settling behavior and physiological characteristics of S. limbatus postlarvae and their implication for aquaculture.

Feeding behaviour and differential absorption of nutrients in mussel Mytilus galloprovincialis: Responses to three microalgae diets

We aimed to evaluate three defined monoalgal diets, Isochrysis galbana clone T-ISO, Tetraselmis suecica and Rhodomonas lens, as a food source for Mytilus galloprovincialis to ascertain which of the diets maximized the feeding, digestion and the assimilatory balance of nutrients and energy. Mussels fed with Rhodomonas yielded the highest clearance and ingestion rates (CR and IR), suggesting that the dimensions of Tetraselmis and T-ISO might have restricted their capture by the mussels’ gill. Absorption efficiency (AE), an indicator of digestibility, was significantly higher for Rhodomonas (69.6%) than for Tetraselmis (38.4%) or T-ISO (23.6%) diets. This could be explained by the greater proportion of refractive non-digestible material contained in Tetraselmis and T-ISO diets, together with the low digestibility of the cell wall of Tetraselmis. The Rhodomonas diet showed the highest protein content, which was reflected in the highest ingestion and absorption of proteins compared with the other diets. However, the amount of carbohydrates and lipids ingested did not match the amount absorbed, probably owing to inefficient carbohydrate digestion and lipids lost through metabolic fecal losses. The total energy absorbed was higher for Rhodomonas (34.5 Jh− 1) than for T-ISO (20.1 J h− 1) or Tetraselmis (13.9 J h− 1) diet. The optimal feeding and digestive behaviour obtained for mussels fed with Rhodomonas diet, coupled with its ideal size, volume, weight and biochemical composition, might provide a better coverage for the anabolic demands of proteins during the seasonal growth cycle, especially during shell formation, gametogenesis and byssogenesis. We state that this manuscript is relevant for the field of bivalve aquaculture and hatchery. We recommend that the main criteria in selecting algae for culturing mussels should be based on choosing the suitable dimension (size, volume, weight) of algal cell depending on the feeding capacity of mussels, which might vary between species and life stages (larvae, adult). The second main criteria should be based on selecting algae with high digestibility and balanced biochemical composition, to obtain a high absorption of energy that covers the nutritional requirements of each life stage of the mussels.

Growth and development time of subtropical Cladocera Diaphanosoma birgei Korinek, 1981 fed with different microalgal diets.

The aim of this work was to investigate the growth performance of Diaphanosoma birgei fed with two Chlorophyceae algae, Ankistrodesmus gracilis and Haematococcus pluvialis using monoalgal diets and simpler mixed diets. D. birgei was daily fed on four treatments: 1) 100% Ankistrodesmus gracilis (Ag); 2) 100% Haematoccocus pluvialis (Hp); 3) 25% A. gracilis + 75% H. pluvialis (Ag-25+Hp-75) and 4) 75% A. gracilis + 25% H. pluvialis (Ag-75+Hp-25). The fecundity curve of D. birgei showed that the mixed feed Ag-25+Hp-75 and temperature 24±2°C triggered fast fecundity at approximately two days. The fecundity was low when based only on H. pluvialis (Hp), albeit with greater longevity (19 days) and a higher number of broods (8). D. birgei fed on Ag and Ag-75+Hp-25 diets in this experiment sustained higher growth rate and higher lipid content in these treatments. The present study showed that A. gracilis diet and mixed microalgae diets tested were able to support the egg production and development of D. birgei.

Mitochondrial activity, hemocyte parameters and lipid composition modulation by dietary conditioning in the Pacific oyster Crassostrea gigas

Several parameters can affect membrane lipid composition in bivalves, including diet. Although two fatty acids (FA) 22:6n-3 and 20:5n-3 are essential membrane components, they are sparingly synthesized by bivalves and must be obtained from their diet. Here, effects of dietary modifications of membrane lipid composition were studied at both cellular and subcellular levels in the oyster Crassostrea gigas. To this end, we compared oysters fed two monoalgal diets that differed markedly in their FA composition and a mix of both. As expected, algae impacted phospholipids, in particular 22:6n-3 and 20:5n-3, reflecting differences of dietary microalgae FA composition. Meantime, total saturated FA, total monounsaturated FA, total polyunsaturated FA and total non-methylene-interrupted FA varied little and phospholipid class composition was only slightly affected by diets. Measures made in hemocytes indicated that only mitochondrial membrane potential was affected by diets. Total ROS production as well as mitochondrial superoxide production did not differ with diet. There was no difference in phosphorylating (state 3) and non-phosphorylating (state 4) rates of oxygen consumption rates or in cytochrome c oxidase activity of mitochondria isolated from gills between the three diets. Similarly, neither cytochromes a, b, c or c1 content nor citrate synthase activities were changed, suggesting that number and morphology of mitochondria were not affected by dietary treatment. These results suggest that oysters could possess high homeostatic capabilities, at both cellular and subcellular levels, to minimize the effect of dietary FA and related membrane lipid FA modifications on mitochondrial functions. These capabilities could be a means to face variations in diet composition in their natural environment and to preserve important oyster physiological functions such as growth and reproduction.

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.

Reproduction and respiration of a climate change indicator species: effect of temperature and variable food in the copepod Centropages chierchiae

The abundance of the calanoid copepod Centropages chierchiae has increased at the northern limits of its distribution in recent decades, mainly due to oceanic climate forcing, suggesting this as a key species in monitoring climate change. Laboratory experiments were conducted to study the combined effect of temperature, food type and concentration on the egg production rate (EPR) and hatching success (HS) of C. chierchiae. Females were fed on two monoalgal diets (Gymnodinium sp. and Phaeodactylum tricornutum) at two food concentrations and at three different temperatures (13, 19, 24°C). Respiration rates of both genders were measured at four different temperatures (8, 13, 19, 24°C). EPR was significantly different between temperatures and food concentrations, the maximum EPR being attained when the copepods were exposed to high food levels and at 19°C. Prey type significantly influenced EPR; feeding on P. tricornutum resulted in higher egg production than Gymnodinium sp. HS was significantly lower at 13°C than at 19 and 24°C and higher with Gymnodinium sp. Respiration rates were sex independent and increased exponentially with temperature. To maintain basal metabolism, the minimum food intake of P. tricornutum ranged between 0.4 and 1.8 µg C and for Gymnodinium sp. between 0.03 and 0.13 µg C. Food intake was always higher than the metabolic demands, except for the highest temperature tested (24°C). The present results confirm the sensitivity of C. chierchiae to temperature variations and may help in understanding the successful expansion of its distribution towards northern latitudes.

Effects of different monoalgal diets on egg production, hatching success and apoptosis induction in a Mediterranean population of the calanoid copepod Acartia tonsa (Dana)

The influence of six monoalgal diets was tested on the reproductive success of the copepod Acartia tonsa over a 15-day period in order to define the most favorable diet for the optimization of this copepod species to be used in aquaculture and in ecotoxicology applications. The cryptophytes Rhinomonas reticulata and Rhodomonas baltica induced highest egg production rates (mean=24.4eggsfemale−1day−1and 21.9eggsfemale−1day−1) and hatching success (mean=76% and 86.1%) over the 15-day period, respectively. Lowest egg production rates were recorded with both diatoms Phaeodactylum tricornutum (mean=8.8eggsfemale−1day−1) and Skeletonema marinoi (mean=8.4eggsfemale−1day−1). These two diatoms also had detrimental effects on hatching success (mean=44.1% and 46.5%, respectively) and adult survival. No adults survived for longer than 13days with a diet of P. tricornutum. Moreover, nauplii produced by females that had fed on diatoms for >10 d, were positively stained for the apoptotic fluorescent marker TUNEL, indicating imminent death. The prasinophyta Tetraselmis suecica induced low fecundity (mean=13.4eggsfemale−1day−1) and hatching success (mean=62%), and after 15days only 37.5% of the adults survived. Isochrysis galbana induced low egg production per female (<10eggsfemale−1day−1) after 15days.

Gut fluorescence analysis of barnacle larvae: An approach to quantify the ingested food

Gut fluorescence analysis can provide a snapshot of ingested food and has been employed in feeding studies of various organisms. In this study we standardised the gut fluorescence method using laboratory-reared barnacle larvae (Balanus amphitrite) fed with mono-algal diet Chaetoceros calcitrans, a unicellular diatom at a cell concentration of 2×105cellsml−1. The gut fluorescence of IV–VI instar nauplii was found to be 370(±12)ng chlorophyll a larva−1 and in faecal pellets it was 224(±63)ng chlorophyll a larva−1. A phaeopigment concentration in larval gut was found to be 311(±13)ng larva−1 and in faecal pellets it was 172(±61)nglarva−1. The study also analysed larval samples collected from the field during different seasons from a tropical environment influenced by monsoons (Dona Paula bay, Goa, west coast of India), with characteristic temporal variations in phytoplankton abundance and diversity. Gut fluorescence of larvae obtained during the post-monsoon season was consistently higher when compared to the pre-monsoon season, suggesting the predominance of autotrophic forms in the larval gut during the post-monsoon season. Whereas, the low gut fluorescence obtained during the pre-monsoon season indicated the ingestion of food sources other than autotrophs. Such differences observed in the feeding behaviour of larvae could be due to differential availability of food for the larvae during different seasons and indicate the capability of larvae to feed on wide range of food sources. This study shows the value of the fluorescence method in feeding studies of planktotrophic organisms and in the evaluation of ecosystem dynamics.