Wild Zooplankton Research Articles

Captive-reared Delta Smelt (Hypomesus transpacificus) exhibit high survival in natural conditions using in situ enclosures.

Conservation of endangered fishes commonly includes captive breeding, applied research, and management. Since 1996, a captive breeding program has existed for the federally threatened and California endangered Delta Smelt Hypomesus transpacificus, an osmerid fish endemic to the upper San Francisco Estuary. Although this program serves as a captive refuge population, with experimental releases being initiated to supplement the wild population, it was uncertain how individuals would survive, feed, and maintain condition outside hatchery conditions. We evaluated this and the effects of three enclosure designs (41% open, 63% open, and 63% open with partial outer mesh wrap) on growth, survival, and feeding efficacy of cultured Delta Smelt at two locations (Sacramento River near Rio Vista, CA and in Sacramento River Deepwater Ship Channel) in the wild. Enclosures exposed fish to semi-natural conditions (ambient environmental fluctuations and wild food resources) but prevented escape and predation. After four weeks, survival was high for all enclosure types (94-100%) at both locations. The change in condition and weight was variable between sites, increasing at the first location but decreasing at the second location. Gut content analysis showed that fish consumed wild zooplankton that came into the enclosures. Cumulatively, results show that captive-reared Delta Smelt can survive and forage successfully when housed in enclosures under semi-natural conditions in the wild. When comparing enclosure types, we observed no significant difference in fish weight changes (p = 0.58-0.81 across sites). The success of housing captive-reared Delta Smelt in enclosures in the wild provides preliminary evidence that these fish may be suitable to supplement the wild population in the San Francisco Estuary. Furthermore, these enclosures are a new tool to test the efficacy of habitat management actions or to acclimate fish to wild conditions as a soft release strategy for recently initiated supplementation efforts.

Live diet for first feeding of Brazilian sardine, Sardinella brasiliensis (STEINDACHNER, 1879), larvae in captivity

Previous studies indicate that Brazilian sardine can be produced in captivity as an alternative to fishing their overexploited stock. However, no research has been conducted about how to improve efficiency in larviculture, a bottleneck phase in aquaculture. Therefore, the aim of this study was to define the optimal live diet in the first feeding of Brazilian sardine larvae, testing five diets of (a) microalgae, (b) rotifer, (c) microalgae plus rotifer, (d) microalgae plus enriched rotifer and (e) microalgae plus wild zooplankton. After eight days, the larvae were sampled to verify survival, growth, digestive enzyme activities (lipase and alkaline protease) and RNA:DNA ratio. Separately, microalgae and rotifer were not enough to support the larvae, resulting in low survival (0% and 3.2 ± 2.9% respectively). However, when offered together they promoted higher survival (up to 40 ± 7.3%). Diets of rotifer enriched with oil emulsion or not produced similar growth (9.23 ± 0.16 mm and 9.13 ± 0.13 mm length respectively). The ingestion of microalgae plus zooplankton significantly increased larvae growth (10.26 ± 0.25 mm length and 2.49 ± 0.20 mg weight), lipase activity and RNA:DNA ratio after eight days. Therefore, the first feeding of Brazilian sardine larvae has better results when microalgae and zooplankton are offered together.

Effects of salinity, stocking density and feeding in Macrobrachium pantanalense larviculture

Macrobrachium pantanalense is a recently described endemic shrimp from Pantanal. The species completes its life cycle in freshwater and is used as an ornamental species for freshwater aquaria, as well as a model organism in risk assessment trials of anthropic impacts. However, all risk assessment trials performed to date have used wild specimens. As such, it is paramount to standardize the laboratory culture of M. pantanalense to allow the use of cultured specimens that safeguard the reliability and replicability of trials being performed. The present work evaluated the use of freshwater and different salinity levels (2, 4 and 6) for the larviculture of M. pantanalense, as well as larval stocking densities of 20, 40 and 60 larvae L−1. Six different larval feeding regimes were also evaluated: 100 % newly hatched Artemia nauplii (AN), 100 % wild zooplankton (WZ), 100 % inert diet (ID), 50 % AN + 50 % WZ, 50 % AN + 50 % ID and 50 % WZ + 50 % ID. Larvae of M. pantanalense were able to successfully metamorphose to post larvae (PL) when cultured in freshwater, although a higher % of PL was achieved under a salinity of 4 (25.6 ± 15.0 %). No significant differences were recorded in survival under different stocking densities. The best larval feeding regime tested was 100AN, promoting a higher production of PL (44.3 ± 18.3 %) when compared with other diets. Overall, the larviculture of M. pantanalense can be enhanced by using brackish water instead of freshwater. By employing a moderate larval stocking density (up to 60 larvae L−1) and an easy to use “of-the-shelf” larval live feed (Artemia nauplii) PL of M. pantanalense can be produced in the laboratory. The present findings are a first step towards the development of a production protocol for M. pantanalense in the laboratory to perform risk assessment trials of growing anthropic stressors impacting Pantanal.

NextGen molecular barcoding of larval grouper diet in an extensive green-water pond system

Molecular barcoding and next generation amplicon sequencing were used to investigate the diet of the larvae of two species: tiger (Epinephelus fuscoguttatus) and hybrid (E. lanceolatus × E. fuscoguttatus) grouper. Larvae were reared in open green-water ponds. These ponds had natural populations of wild zooplankton, and were also seeded with additional zooplankton. Zooplankton from water samples and larvae were collected daily for the first 12 days post hatch (dph) for hybrid grouper and the first 6 dph for tiger grouper. Next generation (NextGen) sequencing with degenerate cytochrome oxidase 1 oligonucleotide primers was performed on all samples. Resulting sequences suggest that both grouper species predated heavily on calanoid copepods – especially at first feeding and while still drawing energy from endogenous supplies. In addition, tiger grouper consumed mussel trochophores as a first feed. Grouper larvae diversified their diets at 6 dph and hybrid grouper were found to be consuming an unidentified insect as their primary food source from this point. Diets further diversified at 10 dph and the first substantial representation of ‘traditional’ aquaculture live feed was seen at 12 dph with the appearance of Artemia. Rotifers (Brachionus spp.) were consumed at a low level by tiger grouper larvae and at a negligible level by hybrid grouper despite daily addition to the pond systems. This study confirms that within the first 12 dph calanoid copepods are the key prey zooplankton for grouper larvae, and demonstrates that NextGen sequencing is a powerful tool for diet assessment in aquaculture.

Short-term lecithin enrichments can enhance the phospholipid and DHA contents of the polar lipid fraction of Artemia nauplii

Wild copepods are the main natural diet of marine finfish and they meet the larvae's requirements in phospholipids and essential fatty acids (EFA). While Artemia nauplii are an easier and more reliable live feed to produce in hatcheries for marine fish larvae than wild zooplankton, enrichment products commercially used lack phospholipids and essential long-chain polyunsaturated fatty acids (LC-PUFA). This is particularly true for docosahexaenoic acid (DHA) within their polar lipid fraction (PLDHA), which is critical to the survival and good development of the larvae. In this study, we showed that it is possible to increase the levels of phospholipids and DHA within the PL fraction of Artemia nauplii using marine lecithin through a process referred to as “boosting”. A cheaper alternative to marine lecithin, soya lecithin, was also tested but resulted only in a significant increase of the phospholipid content of the nauplii with no positive effect on the essential LC-PUFA levels, due to the absence of LC-PUFA in the soya lecithin. This study also showed that the levels of PLDHA in the Artemia boosted with marine lecithin did not reflect the levels of PLDHA in the lecithin, highlighting there the complexity of the boosting process. Finally, chilling enriched Artemia nauplii at 5 °C for up to 10 h did not impact on their nutritional quality post-enrichment. Ultimately, this study proposes innovative and sound enrichment strategies to produce Artemia nauplii rich in EFA and/or PL, similarly to that of the wild copepods' lipid profile.

Integrating of the seahorse <i>Hippocampus reidi</i> in multi-trophic organic farms of oysters and shrimp: Effects of density and diet

The goal of this study was to demonstrate the feasibility of culturing the seahorse Hippocampus reidi in an organic integrated multi-trophic aquaculture farm that produces the oyster Crassostrea brasiliana and the shrimp Litopenaeus vannamei. Experiments were conducted to evaluate the effects stocking density and food (natural zooplankton, Artemia nauplii, or both) for the juvenile I, which are fish from 1 to 15 days after birth. Stocking density effect was studied on growth and survival of juveniles II from 30 days to commercial size in net cages. Survival of the juvenile I was not affected by stocking densities from 2 to 5 ind L-1 and was greater than 70% in all treatments. Seahorse length, however, was inversely related to stocking density. Both treatments with wild zooplankton promoted higher seahorse survival and growth than diet composed exclusively by Artemia sp. during the first 15 days of life. Juvenile II growth decreased with stocking density from 5 to 40 ind m-3 but survival was not affected by it. The total benefit and proportion of colored animals increased significantly with stocking density. The present study confirms the technical feasibility of organic multi-trophic seahorse production in net cages. Even at the highest density tested the seahorses grew well and could generate high profits.

Improved survival, prey selectivity and diel feeding cycle of silver therapon Leiopotherapon plumbeus (Perciformes: Terapontidae) larvae reared in tanks with substrate

Physical substrates in the rearing environment can influence the early survival and feeding patterns of captive-reared fish. In this study, we determined whether substrates affect the survival and growth of hatchery-reared silver therapon Leiopotherapon plumbeus larvae as well as examined their prey selectivity and diel feeding cycle. Newly hatched larvae [1.92 mm total length (TL)] were reared for 40 days in triplicate 4 m3 tanks with or without tropical almond Terminalia catappa leaves as substrate. Prey selectivity of larvae reared in tanks with substrate for 35 days from the yolk-sac stage was measured by the Chesson’s selectivity index (αi). Diel feeding cycle of 3-4 days post-hatch (dph) silver therapon larvae reared in tanks exposed to natural light cycle and fed wild zooplankton was also studied. Larvae reared in tanks with substrate had significantly higher survivorship (48.44 ± 7.85%) than those reared in tanks without substrate (26.73 ± 1.60%). However, total length, specific growth rate and body weight of silver therapon larvae from tanks with or without substrate were not significantly different. Silver therapon larvae are generalist predator, demonstrating a degree of prey selectivity in some prey items during early ontogeny. Prey selectivity of silver therapon larvae varied during larval ontogeny, with higher Chesson’s selectivity index for copepod nauplii among the smaller fish larvae (2–5 dph; 2.94–5.17 mm TL), cladocerans (Moina micrura and Bosmina coregoni) among intermediate (6–11 dph; 5.72–9.60 mm TL), and ostracod, cladoceran and insect larvae among larger fish (12–35 dph; 10.28–20.96 mm TL). Larvae showed a diel feeding cycle where they actively fed during daylight hours, with a peak in the late afternoon, and reached a minimum at dark. Together, these findings advance our understanding of the feeding predatory behavior and efficiency of silver therapon larvae and preference for tanks with substrate that improve their survival.

A method for Rearing Perch, Perca fluviatilis, Larvae Using Paramecium caudatum, Followed by Wild Zooplankton and Formulated Dry Feed in Combination With Adequate Tank Systems

The present study investigates methods for larviculture and fingerling production in the European perch, Perca fluviatilis. Perch larvae in the stage of first feeding were sensitive to many manipulations necessary in fish culture. Lowering and increasing the tank water level as required for cleaning and water renewal, water flow and aeration led to disturbed buoyancy or mortality in a distinct percentage of larvae. Paramecium caudatum, wild zooplankton containing > 70% copeopds, and formulated dry feed were used for first feeding in combination with flow through tanks or static tanks. For first feeding Paramecium caudatum in combination with a static tank system was optimal resulting in survival rates of circa 90% at 15 days post hatch (dph). Wild zooplankton was no optimal starter feed as perch fed non-selectively on any feed particle available. This resulted in moderate survival rates of circa 50% at 15 dph. First feeding with formulated dry feed caused malformations (enlargement of swimbladders) and a high mortality of > 80%. Weaning from Paramecium caudatum to formulated dry feed and to zooplankton was tested on 8-16 dph larvae. Perch accepted the new food type within 3 days. The optimal time point for zooplankton weaning was 12 dph. In this age larvae had developed a selective feeding behaviour, and fed mainly on nauplii and copepodites. Weaning to formulated dry feed was impossible as larvae developed malformations resulting in high mortality as described above. Weaning from wild zooplankton to formulated dry feed was possible for larvae ≥ 29 dph. No cannibalism was observed in the experiments. The method was also tested in large scale experiments resulting in a survival rate of 65±4%, a total length of 45.0±7.2 mm, and a body weight of 1097±293 mg at 75 dph.

Effects of supplemental wild zooplankton on prey preference, mouth gape, osteological development and survival in first feeding cultured larval yellow tang (Zebrasoma flavescens)

Yellow Tang, Zebrasoma flavescens, are a popular species in the aquarium industry. Currently, all Yellow Tang are collected from wild stocks, with collection in Hawaii accounting for the bulk of the individuals found in the trade. Although culture of this species has recently been successful, survival remains low and mass mortality events, particularly associated with the transition from endogenous to exogenous feeding, continue to be observed. Improving survival and gaining a more thorough understanding of the drivers behind early prey selection, such as mouth gape and osteological development, are of primary importance in advancing the culture of Yellow Tang. For the present study, a supplemental size-sorted mixture of wild zooplankton was offered in conjunction with and compared to the cultured nauplii of Parvocalanus crassirostris to determine the effect on survival. Prey selection was determined via metabarcoding. Osteological development was documented and mouth gape measured from 1 to 6 days post hatch to better determine appropriate prey types and size ranges. Survival was significantly lower in larvae fed cultured nauplii supplemented with wild zooplankton, 6.9% v. 18.5%. Regardless of the presence of wild zooplankton, larvae preferentially selected for P. crassirostris based on molecular determination of prey consumption. However, it is likely that protozoans were mostly excluded from this molecular analysis possibly due to the type of primer selected. Mouth gape height increased by approximately 100 μm and mouth gape width by approximately 55 μm, during the study period. Although no significant difference in growth was calculated between treatments, larvae receiving the wild zooplankton supplement diet were observed to grow at a slightly slower rate than larvae being fed only cultured copepod nauplii. The rate at which the mouth gape increased suggests that the currently cultured and utilized copepod nauplii may not be an optimally sized prey item shortly after first feed. These findings indicate that first feeding Yellow Tang larvae are capable of consuming larger prey at an earlier age than they have been offered in previous rearing attempts, but that the larvae may continue to benefit from the presence of less elusive prey items, such as ciliates or rotifers, due to their delayed osteological development. Osteological development was slow with very little ossification occurring by 6 days post hatch and only in those larvae fed solely cultured nauplii. However, their selection of copepod nauplii suggests that some aspect of this prey item is preferential to the first feeding larvae and may elicit a hunting response essential to initiating exogenous feeding.

Captive broodstock development, breeding and seed production of Anthid fish (family: Serranidae) Marcia's anthias, Pseudanthias marcia in recirculation aquaculture system (RAS)

Marcia's anthias, Pseudanthias marcia Randall and Hoover, 1993, belonging to the subfamily Anthiinae (family: Serranidae) is a highly sought after marine ornamental fish mainly due to its vibrant pink shade. The present study reports the first successful captive brood stock development, spawning, and larval rearing of P. marcia. Brood stock was developed in a 5-ton recirculation aquaculture system (RAS) using 12 wild caught juveniles. After 6 months of rearing, the fish (8–9.5 cm size) started courtship behavior. Spawning occurred at 1900 to 2100 h. The eggs (mean size - 617.9 ± 14.9 μ) were transparent, pelagic, non-adhesive and with single oil globule. The eggs hatched out after an incubation period of about 14–16 h at a water temperature of 29 °C. Newly hatched larvae measured 1206.6 ± 100.02 μ in total average length and increased to 1852.9 ± 24.68 μ at 48 h post hatch (ph). Mouth opened at 48–50 h post hatch (ph) and measured 76 to 80 μ. Larval rearing trials were conducted using rotifer (L and S type), wild zooplankton, copepod nauplii, artemia nauplii and microparticulate diet. Primordial fin development started by the 10th day post-hatching (dph) (larval size ~2.9 mm) while the opercular and dorsal spines were fully formed by 15 dph (total length of the larva was 4.4 mm). Larvae metamorphosed to miniature adult shape by 32–34 dph and on 50 dph they reached the pink colored juvenile stage (42–43 mm) and at this stage, they were transferred to nursery rearing tank. Four treatments with different feed combination were tried and treatment III with wild copepod gave an average survival of 5.2 ± 1.07% and treatment IV with Parvocalanus crassirostris gave an average survival of 7.3 (±2.51) %.

Effects of wild zooplankton versus enriched rotifers and Artemia on the biochemical composition of Atlantic cod (Gadus morhua) larvae

Diet at start feeding can affect fish development, pigmentation and growth, and live feed can provide all the dietary requirements of larvae. Enriched rotifers and Artemia are normally used as live feed in the first stages of commercial larval production, however, wild zooplankton or copepods provide better results. The goal of this study was to evaluate whether supplementing enriched rotifers and Artemia (RA) with fish protein hydrolysate (RA-PH) or a small amount of wild zooplankton (RA-Zoo; 5–10% of total prey items) would improve the nutritional quality of larval cod (Gadus morhua), and how it correlated with larval growth rates. Wild zooplankton had significantly higher proportions of the polyunsaturated fatty acids 22:6ω3 (DHA, 23%) and 20:5ω3 (EPA, 11%). Larvae fed wild zooplankton also had higher proportions of essential omega-3 fatty acids (43% RA-Zoo; ≈39–40% RA/RA-PH) and much higher EPA/ARA ratios compared to those only fed with enriched rotifers and Artemia or these prey items plus protein hydrolysate (≈4 RA-Zoo; ≈1.3–3 RA/RA-PH). Further, these fatty acid proportions correlated significantly with larval growth rates and improved fish development. Based on these results, we recommend the inclusion of small amounts of wild zooplankton or commercially produced copepods with high proportions of DHA and EPA, and low proportions of ARA, in the initial diet of Atlantic cod larvae.

A workflow management system for early feeding of the European hake

Diversification of marine species has emerged as a priority in the aquaculture agenda of many countries due to its large industrial potential and as an alternative to overharvested fisheries. Aquaculture diversification entails new challenges during early life stages of candidate species such as survival bottlenecks or body malformations, many of them due to uncoupling between classic diets and early nutritional requirements. Monospecific diets are common in fish aquaculture, e.g. beginning with a rotifer-based diet, followed by a mixed diet of rotifer and artemia nauplii and ending with artemia nauplii and metanauplii until weaning. Despite some success was reported using such protocol in early hake feeding the massive mortality observed as approaching 25dph makes optimization of early feeding and larval management a current challenge for the domestication of this species. The main goal of this study was to design and test a workflow management system for early feeding of the European hake as a candidate species. The null hypothesis tested was that optimization of rearing settings had no effect on early growth and survival up to 30dph as compared to classic culture protocols using commercial prey. Absence of prey in 6dph hake larvae stomachs indicates that their external feeding at 14°C begins just after that age. Early feeding preference depends on prey size (<500μm before 9dph) as well as on pigmentation and behavior e.g. those with poor escape reactivity such as A. franciscana Nauplii. Significant feeding specialization on wild zooplankton such as P. intermedius and T. longicornis occurred after 9dph (Chesson selectivity index=0.11). Feeding activity was maximal in darkness (D) and medium light intensity (600lx, MLI) as compared to the lethal light intensity of 1700lx (HLI). Rotifer-based diets entailed low larvae growth and hake culture unviability after 15dph but inclusion of wild zooplankton in early diets doubled growth of 30dph larvae regarding artemia-based diets. The adaptive prey-size diet designed (MiACop) by combining stages of copepods (nauplii, copepodite and adult), rotifer and commercial nauplii of artemia was five-fold superior to the artemia/zooplankton diet all along the first 30dph larvae culture. The massive cannibalism observed from 25dph on was related to the absence of an adequate prey size such as that of mysids and euphausiids in combination with semi-dry feed to trigger weaning. Current workflow design for early feeding of the European hake can be helpful to assuring a larger proportion of juveniles entering the weaning phase. Statement of relevanceFirst feeding of the European hake.

Transcriptome profiling reveals that feeding wild zooplankton to larval Atlantic cod (Gadus morhua) influences suites of genes involved in oxidation-reduction, mitosis, and selenium homeostasis.

BackgroundLarval nutrition and growth are key issues for wild and cultured cod. While it was shown previously that larval cod fed wild zooplankton grow faster than those fed only rotifers, the mechanisms involved in this enhanced growth are not completely understood. We used microarrays to identify larval cod transcripts that respond to feeding with small amounts of wild zooplankton (5–10 % of live prey items). The larval transcriptome was compared between 3 treatment groups [fed rotifers (RA), rotifers with protein hydrolysate (RA-PH), or rotifers with zooplankton (RA-Zoo)] at 9–10 mm length [26–30 days post-hatch (dph)] to identify a robust suite of zooplankton-responsive genes (i.e. differentially expressed between RA-Zoo and both other groups).ResultsThe microarray experiment identified 147 significantly up-regulated and 156 significantly down-regulated features in RA-Zoo compared with both RA and RA-PH. Gene ontology terms overrepresented in the RA-Zoo responsive gene set included “response to selenium ion” and several related to cell division and oxidation-reduction. Ten selenoprotein-encoding genes, and 2 genes involved in thyroid hormone generation, were up-regulated in RA-Zoo compared with both other groups. Hierarchical clustering of RA-Zoo responsive genes involved in oxidation-reduction and selenium homeostasis demonstrated that only the zooplankton treatment had a considerable and consistent impact on the expression of these genes. Fourteen microarray-identified genes were selected for QPCR involving 9–13 mm larvae, and 13 of these were validated as differentially expressed between RA-Zoo and both other groups at ~9 mm. In contrast, in age-matched (34–35 dph; ~11 mm RA and RA-PH, ~13 mm RA-Zoo) and size-matched (~13 mm) older larvae, only 2 and 3 genes, respectively, showed the same direction of RA-Zoo-responsive change as in ~9 mm larvae.ConclusionsThe modulation of genes involved in selenium binding, redox homeostasis, and thyroid hormone generation in ~9 mm RA-Zoo larvae in this study may be in response to the relatively high levels of selenium, iodine, and LC-PUFA (potentially causing oxidative stress) in zooplankton. Nonetheless, only a subset of zooplankton-responsive genes in ~9 mm larvae remained so in older larvae, suggesting that the observed transcriptome changes are largely involved in initiating the period of growth enhancement.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2120-1) contains supplementary material, which is available to authorized users.

A Little Goes a Long Way: Improved growth in Atlantic cod (Gadus morhua) fed small amounts of wild zooplankton

We examined the effects of partial dietary supplementation with wild zooplankton or fish protein hydrolysate on cod production traits, and how they related to the expression of growth and appetite regulating transcripts and muscle cellularity. Atlantic cod larvae were fed three different diets: enriched rotifers and Artemia (RA); RA+fish protein hydrolysate (RA-PH); and RA supplemented with 5–10% wild zooplankton (RA-Zoo). Partial supplementation with zooplankton significantly improved cod dry weight at 60days post-hatch (by approximately 4-fold), specific growth rate (by 2.5% day−1) and the general development of cod larvae. Although the zooplankton fed cod were still larger at approximately 1.5years of age, the growth advantage of this group decreased with age (the difference in wet mass decreasing from approximately 30% at 0.5years old to 11% at 1.5years old). In contrast, the protein hydrolysate enrichment did not improve growth, had a negative effect on survival, and increased the incidence of external deformities in 1.5year old fish. The growth enhancement observed in the RA-Zoo larvae was largely unrelated to differences in the transcript levels of several important growth [Insulin-Like Growth Factor 1 (igf-1); igf-2; Growth Hormone (gh); GH Receptor-1 (ghr-1); ghr-2; and myostatin (mstn)] or appetite regulating genes [Cocaine and Amphetamine Regulated Transcript (cart) and Neuropeptide Y (npy)], but was associated with an increase in the number and size of skeletal muscle fibers. Our findings suggest that incorporating small amounts of wild zooplankton into larval feeding regimes may significantly enhance the production of marine fishes, but that the transcript levels of the above hormones and hormone receptors are not valuable biomarkers of growth in cod larvae. Statement of relevanceThis research shows that small amounts of zooplankton significantly improve the growth of Atlantic cod larvae, and thus, that cultured zooplankton may be a viable and cost-effective strategy for increasing the growth (and potentially health) of intensively cultured marine finfishes.

Effects of feeding with frozen freshwater cladoceran Moina macrocopa on the performance of red sea bream Pagrus major larviculture

The feeding effects of freshwater cladoceran Moina macrocopa to the larvae and juveniles of red sea bream were investigated. M. macrocopa was mass-cultured with freshwater Chlorella as feed and was enriched nutritionally with a commercial enrichment diet. Because M. macrocopa die in seawater within a few minutes, the cladocerans were frozen after nutritional enrichment. The survival rates, growth rates and stress tolerances of fish fed with enriched M. macrocopa were compared with those fed with enriched Artemia and with zooplankton harvested from open seawater. The fatty acid composition of each type of zooplankton was analyzed. Mass-cultured M. macrocopa could be enriched with a commercial enrichment diet. The DHA/EPA ratio of M. macrocopa was inferior to that of enriched Artemia nauplii and wild zooplankton. Although the growth and stress tolerance of fish fed on frozen M. macrocopa were inferior to those fed with enriched Artemia nauplii and wild zooplankton, their survival rate was superior. It was concluded that frozen and enriched M. macrocopa could be fed to red sea bream larvae and juveniles. However, it is necessary to improve its fatty acid composition, particularly the DHA content.

Características morfológicas, morfométricas, merísticas y manejo de la primera alimentación de larvas de escalar altum (Pterophyllum altum) (Pellegrin, 1903)

El escalar altum ha sido una especie representativa de la ictiofauna suramericana por su amplia aceptación en el mercado de la acuariofilia, lo que lo convierte en una especie con gran potencial productivo. En el presente estudio se realizó una descripción morfológica, detalle de algunos parámetros merísticos de los primeros estadios de vida de larvas de P. altum y aspectos de su primera alimentación. Se utilizaron diez parejas de reproductores mantenidas en acuarios de 50 L, con aireación y temperatura constante. Luego del proceso de reproducción se tomaron 15 larvas/h hasta las 75 horas poseclosión, (HPE) estas fueron fijadas en formol bufferado al 4% para posterior descripción de las características merísticas y morfométricas. Así mismo, se suministraron diferentes dietas luego de la reabsorción del saco vitelino, así: (T1) larvas alimentadas con nauplios de Artemia salina, (T2) cistos de Artemia salina decapsulados, y (T3) zooplancton silvestre para determinar algunos parámetros productivos. Morfológicamente, las larvas de P. altum tienen un cuerpo cilíndrico, redondeado, cola alargada y saco vitelino ovoide evidente hasta su desarrollo en postlarva. En cuanto a sus características morfométricas, presentaron una longitud total promedio de 4.64±0.5 mm, una longitud estándar de 3.8±0.2 mm, el diámetro del ojo de 0.49±0.2 mm, así como una longitud de de cabeza 0.71±0.8 mm y la altura del cuerpo de 0.76±0.6 mm a las 75 HPE. Con el suministro de las diferentes dietas no se observaron diferencias estadísticas significativas (P&gt;0.05), en los pesos finales. Sin embargo, se observaron diferencias (P&lt;0.05) en la tasa de crecimiento especifico y en la sobrevivencia. Como conclusión, las larvas de P. altum presentan un crecimiento acelerado hasta el segundo día de vida, debido a la disminución de la relación entre las características morfométricas. Por otro lado, el mejor desempeño productivo se observó en los individuos alimentados con nauplios de artemia, constituyéndose en una importante alternativa como fuente de alimento durante la larvicultura de esta especie

Condition, survival and growth in situ of hatchery-reared stage IV lobster (Homarus americanus) fed Artemia and lipid-rich wild zooplankton

The release of hatchery-reared American lobster (Homarus americanus) is used, on some occasions, as a tool to enhance depleted lobster stocks. Current Canadian lobster enhancement programs rely on the release of postlarvae (stages IV and V), which are still vulnerable to high mortality. We hypothesized that larvae enriched in triglycerides (TAG) and polyunsaturated fatty acids (PUFA) during their development from stage I to stage IV have higher survival and growth rates. We assessed the condition, growth and survival of lobster postlarvae (stage IV) fed during their larval stages with live natural zooplankton, to maximise TAG and PUFA enrichment, compared to those fed a standard Artemia diet. Stage I larvae obtained from ovigerous wild females were cultured in the hatchery on either an Artemia or a zooplankton diet until stage IV (7d old), when they were transferred to the field (i) individually in small boxes for 3months or (ii) communally in large enclosures for 3–4months to assess survival and growth in situ. Our results show that a diet of natural zooplankton significantly increases the TAG and PUFA content of larvae compared to a diet of live Artemia. Stage IV lobsters fed natural zooplankton had a better condition index (TAG/ST) and a higher activity of the enzyme regulating osmoregulation than those fed Artemia. Larvae fed zooplankton had a significantly higher growth rate than larvae fed Artemia, (655 vs 507μm dry massd−1, respectively). Despite these differences, survival was similar for both diets, in the hatchery as well as in situ, in predator-free situations. Nevertheless, a higher growth rate may be a potential survival advantage for newly released lobsters, allowing them to reach a size refuge from predation more rapidly. We conclude that even if live Artemia remains the best and most reliable source of live food for the production of American lobster larvae, it needs to be considerably enriched with PUFA, at levels comparable to that of natural zooplankton, to increase osmoregulation potential and growth.

Estimating the Food Requirements and Prey Size Spectra of Larval American Shad

AbstractWidespread declines in American shad Alosa sapidissima along the Atlantic coast have been attributed to overfishing, a decrease in water quality, and loss of habitat. Recent surveys along the Roanoke River and Albemarle Sound, North Carolina, suggest that stocks are continuing to decline despite extensive management and stock enhancement efforts. Laboratory experiments were conducted to evaluate the effect of prey density on the growth and survival of American shad and to determine whether larvae can survive and grow in a riverine environment with a limited forage base. Larvae were reared from 11 to 20 d posthatch in one of five treatments: (1) no food; (2) low food (1 prey/L), which simulated the prey densities in the Roanoke River; (3) medium food (50 prey/L), which simulated the prey densities typical of coastal watersheds; (4) high food (500 prey/L); and (5) Artemia spp. (500/L). Larval survival was 35 ± 7% (mean ± SE) and was not significantly different among treatments. Treatments with starved fish had the lowest survival (22 ± 12%), while the highest survival was observed in treatments with high densities of wild zooplankton (46 ± 18%) and Artemia (40 ± 16%). Length‐specific growth rates were 0.017 mm/d for the starved treatments and 0.024, 0.029, 0.034, and 0.039 mm/d for the low‐prey, medium‐prey, high‐prey, and Artemia treatments, respectively. Larval growth as a function of length was not significantly different between the Artemia and high‐prey treatments; however, growth in these treatments was significantly higher than in those with lower prey densities. Weight‐specific growth rates (Gw) were significantly higher for the Artemia treatment (Gw = 0.129) than for all the other treatments (Gw = 0.081). Analysis of stomach contents indicated that American shad were selectively feeding on the smallest zooplankton (80–250 μm) and that larvae exhibited a strong preference for copepod nauplii and rotifers. These results suggest that spatial and temporal overlap between larvae and zooplankton is important for larval growth and survival.Received March 31, 2011; accepted September 12, 2011

Growth, survival and proximate body composition of Labeo rohita larvae fed artificial food and natural food organisms under laboratory condition

This investigation was carried out to study the effect of different live feed and dry feed on growth and survival of Labeo rohita at a stocking density of 20 larvae per trough having 10 L of water. The increase in weights and lengths were used as measures of growth. The duration of the experiment was 30 days. Seven dietary treatments were tested viz. Artificial diet with 45% protein (LFr1), rotifers like Asplanchna and Brachionus (LFr2), wild zooplankton (LFr3), bioenriched zooplankton (raised on Chlorella , cod liver oil and vitamin C) (LFr4), Artemia (LFr5), Chironomous (LFr6) and Oligochaetes (LFr7). Among the different treatments, larvae fed with diet LFr4 resulted in the maximum body weight gain (BWG) (13.18 ± 0.13 mg) which was significantly (P < 0.05) higher than all the treatments which followed the order of preference as: LFr5 (12.31 ± 0.10 mg), LFr3 (9.75 ± 0.08 mg), LFr2 (7.85 ± 0.10 mg), LFr7 (6.49 ± 0.15 mg), LFr6 (5.66 ± 0.13 mg) and LFr1 (4.99 ± 0.14 mg). The diet LFr4 recorded maximum survivability (92.0 ± 2.0%). All the values recorded for the BWG and survival were found to be significantly different (P < 0.05) among others. Protein and lipid content of the prawn after the treatment was found to be highest for LFr5 and LFr4, respectively.

Comparison of growth, digestive system maturation and skeletal development in sea bass larvae reared in an intensive or a mesocosm system

The quality of development in intensive or mesocosm hatchery-reared Dicentrarchus labrax larvae was investigated using physiological indicators assessing ontogeny. Larvae were reared in intensive (120 L tanks) and in mesocosm systems (20 m(3) enclosures) with the same feeding sequence, excluding the wild zooplankton naturally available in mesocosms. Faster growth was recorded since early development [16 day after hatching (DAH)] in the mesocosm. Maturation of the digestive system also occurred earlier as indicated by the higher amylase secretion ratios, the intestinal maturation index (alkaline phosphatase/leucine-alanine peptidase and aminopeptidase-N/leucine-alanine peptidase ratios) and the more developed intestinal epithelium at 23 DAH. Nevertheless, the delay in digestive maturation in the intensive system seemed retrieved within few days. In both the groups, the number of vertebrae ranged between 24 and 26, with the dominant class being 25 vertebrae. However, the distributions differed between treatments for meristic characteristics, ossification stages and incidence of malformation types. Loss of a vertebra was more frequent in the intensive system, while the appearance of an additional vertebra was more frequent in the mesocosm. Ossification at 37 DAH was also more advanced in the mesocosm in addition to a lesser rate and severity of skeletal malformations. It is suggested that the early nutritional contribution of mesocosm wild zooplankton, yet at densities of 0.2-0.7 prey mL(-1), had key effects on larvae development since the early stages.