Gunvor Øie

A review of the nutritional effects of algae in marine fish larvae

In the first-feeding of larval, turbot (Scophthalmus maximus) and halibut (Hippoglossus hippoglossus), microalgae are used in the production of rotifers (Brachionus plicatilis) in order to transfer essential nutrients from the algae to the live food. In addition, the algae may be given directly to the larvae along with the live food. In this circumstance they act both as food for the fish larvae and for the live food. Microalgal addition to the first-feeding tanks along with the rotifers improved growth and survival of larvae, whereas short-term enrichment of rotifers with algae did not improve growth and survival of larvae in tanks without algae added. The algae in larval tanks tended to modify and stabilize the nutritional quality of the rotifers in the period before they were consumed by the larvae. The lipid content and fatty acid composition of the rotifers reflected the composition of the algal diets, and the algal species used may be an effective tool to control the fatty acid content (especially DHA, 22:6n−3, docosahexaenoic acid, and EPA, 20:5n−3, eicosapentaenoic acid). The content of n−3 polyunsaturated fatty acids varied between algal species, and to some extent, with the growth limitation of the algal cells. Young stages of marine fish larvae ingested microalgae, but the algal cells were assimilated to a different extent in halibut and turbot. The ingested microalgae may have triggered the digestion process or contributed to the establishment of an early gut flora. The algae in larval tanks most probably modified the bacterial flora of the water and the rotifers. In addition, the algae in larval tanks may have modified the light milieu for the larvae.

Nutritional effects of algal addition in first-feeding of turbot (Scophthalmus maximus L.) larvae

Abstract The effect which microalgal addition and rotifer enrichment with algae had on survival, growth rate and fry viability during first-feeding were examined for turbot (Scophthalmus maximus L.). Addition of the microalgae Isochrysis galbana or Tetraselmis sp. together with rotifers Brachionus plicatilis, grown on yeast and oil emulsion, and Artemia greatly improved rearing success, whereas short-term enrichment of the rotifers with Tetraselmis sp. gave only improved viability. The algae modified the relative fatty acid composition of rotifers. Rotifers with I. galbana exhibited and increased level of 22:6n-3 and a lower level of 20:5n-3, whereas the opposite change occurred when Tetraselmis sp. was used. Addition of either of the two algal species at 1 mg cl−1 to the larval tanks resulted in a constant lipid level and high egg ratio of the rotifers, and thereby also high individual biomass content. Without algal addition, the lipid content of the rotifers decreased by 20% day−1 in the early phase, and their egg ratio became close to zero. In addition to improved nutritional conditions of the larvae, some other factor, e.g. some trigger mechanism or changed microbial or light conditions, also can operate to explain the increased early appetite of larvae with microalgae added and must be taken into consideration.

Microbially matured water: a technique for selection of a non-opportunistic bacterial flora in water that may improve performance of marine larvae

Before transfer to larval incubators, water was membrane filtered to remove >95% of the bacteria and then transiently maintained in a biofilter that promoted recolonization of the water by non-opportunistic bacteria. The process is termed microbial maturation of the water. Hypothetically the bacterial flora in the matured water should protect the marine larvae from colonization and proliferation by opportunistic bacteria. Testing of the hypothesis demonstrated 76% higher survival of yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus) in matured than in membrane filtered water. Proliferation of opportunistic bacteria was observed in the rearing water after hatching of turbot eggs (Scophthalmus maximus), but to a less extent in the microbially matured water. In the early phase of first feeding of turbot larvae, the matured water induced qualitative differences in the gut microflora. Significantly higher initial growth rate of the turbot larvae in the matured water affected 51% higher average weight of 13 days old larvae than in membrane filtered water. Algal addition to the matured water enhanced the larval growth further. The experiments conducted supported the proposed hypothesis that microbial maturation selects for non-opportunistic bacteria, which protects the marine larvae from proliferation of detrimental opportunistic bacteria.

Protein and carbon utilization of rotifers (Brachionus plicatilis) in first feeding of turbot larvae (Scophthalmus maximus L.)

Abstract The effect of three different rotifer enrichments was examined on growth, survival, pigmentation and viability of first feeding turbot larvae. The diets differed in rotifer content of protein, lipid and ratio of protein/lipid. The diets were fed to turbot with or without algae ( Isochrysis galbana ) added to the larval tanks. The turbot larvae were fed rotifers for 10 days and thereafter the same Artemia diet was fed to all treatments for the rest of the experimental period. Growth and survival of fish larvae were higher in tanks containing algae than in tanks where no algae were added. Independent of algal addition, the highest growth rate and survival was obtained by feeding rotifers containing the highest protein content. Larvae reared in greenwater consumed higher numbers of rotifers during the stagnant period than larvae kept in clearwater conditions, while analysis of the larval gut contents showed lower rotifer numbers in the gut of larvae reared in greenwater conditions. This must imply longer residence time of the food in the larval gut, and presumably also higher digestion and assimilation efficiencies of larvae maintained without algae than in larvae maintained with algae. Calculation of protein and carbon conversion efficiency showed higher utilization in larvae maintained without algae (18–28% for protein, 12–19% for carbon) than in larvae maintained with algae (6–9% for protein, 4–7% for carbon). No significant differences in pigmentation rate and stress sensitivity were observed among the larvae of the various treatments.

Particle size dependent feeding by the rotifer Brachionus plicatilis

AbstractSize selective feeding by Brachionus plicatilis was investigated with algae and bacteria (0.3–3.5 µm) and mono-disperse latex beads (0.3–3.0 µm) in short term feeding experiments. B. plicatilis demonstrated maximum clearance rate of particles with diameter ≥2µm, but particles with diameter down to 0.3 µm were also ingested. The clearance rate of bacteria was 15–55% of that obtained for optimal sized particles (≥2 µm), and was related to particle size. The relative reduction in retention of particles with diameter < 2 µm was more pronounced for latex beads than for natural food particles, suggesting other mechanisms than size to be important for the particle retention by the rotifer. This is emphasized by the fact that the clearance rates were much lower for latex beads than for natural food particles of comparable size. Efficient retention of bacteria was observed for rotifers in poor physiological condition, i.e. rotifers with low maximum clearance rate. This may reflect a strategy to optimize energy utilization by reducing locomotion costs and increasing energy intake.The results indicate that B. plicatilis has a low to medium ability to feed on bacteria. In natural ecosystems, its importance as a bacterial grazer is of limited importance. At high population densities, such as in live feed cultures, the rotifer may, however, efficiently remove bacteria from the culture.

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 (µmax). Except for C. mülleri and N. oculata, the microalgae were thereafter grown semi-continuously at dilution rates of 20% and 60% of µmax 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.

Effects of egg disinfection on yolk sac and first feeding stages of halibut (Hippoglossus hippoglossus L.) larvae

Abstract Halibut eggs were treated with the disinfectant glutaric dialdehyde in two regimes, 400 ppm for 10 min and 800 ppm for 2.5 min. Treatment effects were evaluated by analyses of egg mortality, performance of deformed larvae, survival during the yolk-sac period, and growth and survival during first feeding. To evaluate effects of disinfection on the first feeding stage, two separate feeding regimes, Artemia salina and wild zooplankton, were tested. No significant differences in survival or percentage of deformed larvae were found between the larval groups during the yolk-sac period. Differences in survival appeared during start feeding where eggs exposed to 400 ppm glutaric dialdehyde showed significantly higher survival than did the 800 ppm and control (untreated) group on both food types. The 400 ppm group also showed higher growth, which was most pronounced with wild zooplankton.

Protein and lipid content of the rotifer Brachionus plicatilis during variable growth and feeding condition

Rotifers (Brachionus plicatilis) grown at different growth rate (µ = 0.05−0.39 d−1) were analyzed for protein, lipid, fatty acids, amino acids and free amino acids, and values are expressed in terms of individuals and dry weight. Increase in growth rate is equivalent with increased food ration of the individual rotifer, which responded by higher egg ratio. The protein content per individual rotifer increased by 60–80% when the growth rate increased, whereas the protein content per dry weight showed a slight, although insignificant, increase (p>0.05). The lipid content per individual was constant, whereas lipid per dry weight decreased when the growth rate increased. The ratio DHA/EPA decreased when the growth rates increased. The amino acids profile in percent of total amino acids showed low variation between cultures maintained at different growth rates, whereas the values expressed in terms of amino acid per individual showed higher variation. The range of variation for free amino acids was more pronounced than for total amino acids.

Surface disinfection of Atlantic halibut and turbot eggs with glutaraldehyde: evaluation of concentrations and contact times

To evaluate the effects of glutaraldehyde treatment at different disinfection temperatures, Atlantic halibut, Hippoglossus hippoglossus (L.), and turbot, Scophthalmus maximus (L.), eggs, incubated at 5 and 12°C, respectively, were disinfected with 400–1200 mg glutaraldehyde l-1 at three different contact times (2.5, 5 and 10 min). Egg batches of both poor and good quality were tested for halibut. Positive effects were more pronounced in poor than in good-quality batches at hatching. Egg disinfection had a highly positive effect on the viability of yolk-sac larvae in both types of batches. A level between 400 and 800 mg l-1 at a contact time of 5–10 min was optimal for halibut: at lower levels, the bactericidal effect was reduced, and at higher levels, there were indications of toxic effects. Halibut eggs disinfected with optimal doses of glutaraldehyde had furthermore a reduced hatching time and more synchronous hatching as compared with untreated eggs. Turbot was more sensitive to higher doses than halibut, and the best larval performance was obtained for 400–800 mg glutaraldehyde l-1 at a contact time of 2.5 min. A further evaluation should, however, be performed before recommendations are given for species incubated at temperatures higher than 5°C.

Molecular ontogenesis of digestive capability and associated endocrine control in Atlantic cod (Gadus morhua) larvae.

We have profiled the expression of twelve genes, in order to provide an overview on the molecular ontogeny of digestive capability with the associated endocrine control during Atlantic cod (Gadus morhua) larval development. Enzyme activity levels for the key digestive enzyme, trypsin, was also measured. Specifically, transcripts for trypsin, amylase, lipolytic enzymes: bile salt activated lipase (BAL), phospholipase A2 (PLA2) and Acyl CoA dehydrogenase (ACADM), regulatory peptides: neuropeptide Y (NPY), orexin (OX) cholecystokinin (CCK) and cocaine and amphetamine-related transcript (CART), the somatotropic factors: growth hormone (GH), preprosomatostatin 1 (PPSS1) and thyroid hormone receptors (TRα and TRβ) were analyzed using quatitative (real-time) polymerase chain reaction (qPCR). Trypsin and BAL mRNA levels peaked at approximately day 17 and 25 post-hatch, respectively, and thereafter displayed a decreasing pattern until metamorphosis. GH mRNA levels decreased moderately from 3 to 33dph, and thereafter, an increase was observed until 46dph. TRα mRNA levels showed a fluctuating pattern peaking at day 39 post-hatch. TRβ mRNA levels were too low to obtain quantitative measurements. Amylase mRNA slightly increased from day 3 to 17 post-hatch, and thereafter showed a steady decrease until day 60. Interestingly, PLA2 mRNA expression showed a consistent increase throughout the study period, indicating an increasingly important role during larval development. Overall, data from this study indicate that cod larvae show differential developmental mode of expression patterns for key genes and endocrine factors that regulate digestive capability, growth and development. These data are discussed in relation to larval trypsin enzyme activity and previous reports for other teleost species.