Detection of tetrodotoxin-producing Providencia rettgeri T892 in Lagocephalus pufferfish

Tetrodotoxin (TTX) is a potent toxin but it could be used in pharmaceutical field. Identification of TTX producing bacteria in pufferfish is necessary for TTX yield and the pufferfish conservation. In this study, Lagocephalus was collected from Cam Ranh Sea, a central part of Vietnam during spring season. The liver and intestine were incubated in 0.9 % NaCl for TTX detection in pufferfish. To be benefited from the isolation of new TTX producing bacteria, the liver and intestine were incubated in 6.5 % NaCl. The cultures were used to test the toxin and to isolate the bacterial community that could yield TTX. Surprisingly, Providencia rettgeri T892 in intestine could produce TTX identified by biochemical test and 16S rRNA sequencing. This strain was used to test the production of TTX, based on thin layer chromatography (TLC), mouse bioassay and high performance liquid chromatography (HPLC) analysis. The bacterium was optimized for TTX production in media prepared from the meat-washing water of Auxis thazard, Megalaspis cordyla and Decapterus maruadsi. Interestingly, the TTX obtained 0.106 mg/mL and 0.055 mg/mL in medium prepared from A. thazard and M. cordyla, respectively while there was no TTX production detected in medium prepared from D. maruadsi. This paper could contribute to warn to the human health care system about a possible TTX poisoning in some cases related to eating fishes.     

Enhanced colonization success and competition associated with conspecifics in cleaner fish Labroides dimidiatus juveniles

The cleaner fish Labroides dimidiatus affects the abundance of many fishes, including their juveniles, yet how they affect the post-settlement processes of conspecifics remains poorly known. Using a long-term experiment, where L. dimidiatus were regularly removed from seven patch reefs (removals) for 10 years or left undisturbed (controls) on nine, the effect of conspecifics’ presence on recently settled L. dimidiatus juveniles and the relationship between juvenile and adult abundance on control reefs were examined. Repeated sampling 4–40 months after manipulating L. dimidiatus revealed that the abundance of juveniles on removals, compared with controls reefs, was 72 % (95 % CI = 65–79 %) lower; this effect did not vary over time. Thus, decreased colonization was associated with resident conspecific absence and this effect was present after 4 months. Since other studies found 4 months of cleaner absence was too short to affect client abundance—a factor also known to enhance L. dimidiatus colonization—it was likely not involved here. Over 10 years, individual control reefs were almost always occupied by at least one adult (89–100 % of times sampled); but in summer, when L. dimidiatus colonization was highest, juvenile abundance was negatively related with adult abundance at one of two sites, with the expected number of juveniles decreasing by 67 % (95 % CI = 51–83 %) with each additional adult. This suggests a deleterious effect of adults on juveniles at one site, such as competition. Enhanced colonization of juveniles associated with adult presence may partly explain the relative permanence of fish cleaning stations.     

The chemosensory responses of young cichlid fish to parents and predators

The chemosensory responses of the fry of the Midas cichlid, Cichlasoma citrinellum (Pisces: Cichlidae), were tested in a Y-maze during their first 11 days of free-swimming. Fry preferred all conspecific females to blank water but did not distinguish between their own mother, another mother or a non-parental, adult female. Fry preferred females to males. Similar results were obtained for males. Fry preferred their siblings and (unrelated) juveniles to blank water. However, while they failed to show a preference between siblings and their mother, they preferred their mother to juveniles. Fry were able to any of three heterospecifics (C. managuense, C. nigrofasciatum and the allopatric Sarotherodon mossambicus). The chemosensory responses demonstrated in the Y-maze are hypothesized to aid the fry in staying near the centre of the guarded territory and away from predators, particularly under murky or nocturnal conditions.     

Growth and migration patterns of juvenile temperate seabass Lateolabrax japonicus in the Yura River estuary,Japan—combination of stable isotope ratio and otolith microstructure analyses

It is important to know the characteristics of migration pattern and vital rates of juveniles to understand the early life history and its effect on the population dynamics of fishes. The relationship between growth and migration pattern of juvenile temperate seabass Lateolabrax japonicus in the Yura River estuary was examined by combination of stable carbon isotope ratio (δ¹³C) and otolith microstructure. Gut fullness indices were also examined to know the feeding condition of juveniles. δ¹³C values of seabass juveniles in the lower estuary and surf zone (LES) were enriched, while those in freshwater zone (FW) were depleted, consistent with δ¹³C differences in prey items. The back-calculated growth rates of juveniles in FW were significantly lower than those of juveniles that resided in the LES from 50 days to 90 days old, implying that juveniles with poor growth ascended the river while those with better growth remained in the LES. However, the growth rates of the juveniles, which resided in FW for more than 1 month, caught up with and even overtook those of juveniles in LES within 1 month after ascended the river. The higher water temperature and better feeding conditions would contribute to better growth rates of juveniles in FW than those in LES.     

Characterization of biocontrol traits of heterorhabditid entomopathogenic nematode isolates from South Benin targeting the termite pest Macrotermes bellicosus

Twenty-nine Beninese isolates of Heterorhabditis sonorensis and one local isolate of H. indica were screened in bioassays for their pathogenicity against Macrotermes bellicosus and for their tolerance to heat (40 °C), desiccation (25 % glycerine) and hypoxic conditions. The bioassays showed significant differences among isolates for all tested traits. Most of the isolates (73 %) killed more than 80 % of the insects. The greatest survival of infective juveniles to heat (8 h), desiccation (8 h), and hypoxia (72 h) was observed with the H. sonorensis isolates Kassehlo (72.8 %), Setto1 (72.5 %), and Kissamey (81.5 %, respectively). Hierarchical cluster analysis identified six clusters. One of the clusters grouped three isolates of H. sonorensis (Zoundomey, Akohoun and Kassehlo) that scored well for all traits. These latter isolates were similarly effective by suppressing within five days a population of M. bellicosus naturally imprisoned in 1,000 cm³ containers and inoculated with a single two-weeks-old EPN-infected Galleria larva.     

Distribution and microhabitat associations of the juveniles of a high-value sea cucumber, <Emphasis Type="Italic">Stichopus</Emphasis> cf. <Emphasis Type="Italic">horrens,</Emphasis> in northern Philippines

There is considerable global interest in rebuilding depleted populations of sea cucumbers (Echinodermata, Holothuroidea) to address conservation and economic goals. For the vast majority of holothurian species, the habitat and food requirements of the juvenile stage are poorly understood. We investigated the distribution and microhabitat associations of juveniles of a commercially important sea cucumber, Stichopus cf. horrens, in the shallow, shoreward side of a coral reef (or backreef) in northern Philippines (16°21′38.7″N, 119°59′47.9″E). Relationships between juvenile density and the physical, chemical and biological characteristics of their habitat were examined. Potential food sources of the juveniles were also investigated using elemental and stable isotope analysis. Results showed that juveniles are more abundant in seagrass areas and the transition zone between seagrass and the rubble-dominated reef flat. A non-metric multidimensional scaling (MDS) plot indicated that juvenile density was most positively associated with coarser sand and rubble (>0.5 mm) and seagrass (Thalassia hemprichii) abundance (2D stress = 0.11). Juvenile density was also positively associated with sediment organic matter from plant detritus to a lesser extent. Elemental and isotope analysis of one site indicated that epiphytes were the primary food source of juveniles, while sediment detritus from microalgae and seagrass was a secondary food source. This study corroborates anecdotal evidence regarding the importance of seagrass to S. cf. horrens as potential refugia and source of high-quality food for its juveniles. These findings underscore the need to protect the nursery habitats of wild juveniles and provide critical information for the selection of suitable natural habitats for releasing cultured juveniles of this important species.     

Realized pollen and seed dispersal within a continuous population of the dioecious coniferous Brazilian pine [Araucaria angustifolia (Bertol.) Kuntze]

Extensive realized pollen and seed flow across populations reduces inbreeding and spatial genetic structure (SGS) and increases the genetic diversity and effective size within populations. Inbreeding, SGS and realized patterns of pollen and seed dispersal of the dioecious, wind pollinated Araucaria angustifolia were investigated based on microsatellite loci. The study was conducted in a 7.2 ha plot established within a continuous Araucaria Forest in Southern Brazil. In the plot, all 290 adult trees were mapped, measured (diameter at breast height, dbh), sexed, sampled and genotyped. We also sampled, measured (total height), mapped and genotyped 223 juveniles. A total of 86 alleles were detected in the sample (n = 513). Adults and juveniles showed a positive and significant fixation index (minimum of 0.096), suggesting inbreeding or Wahlund effect. Juveniles presented a significant aggregated distribution which was associated with a genetic aggregation (significant SGS up to 20 m), indicating that near neighbor trees may be related due the limited seed dispersal. However, the intensity of SGS was not significantly higher among juveniles (Sp = 0.0041) than adults (Sp = 0.0026). Realized pollen and seed immigration into the plot was low (pollen = 6 %; seeds = 5 %) and the patterns of pollen and seed dispersal were similar. Pollen was dispersed over long distances (343 m), but 50 % was dispersed up to 124 m. Seeds also reached long distances (318 m), with 50 % being dispersed up to 133 m. Our results are discussed in terms of auto-ecology and the genetic conservation of A. angustifolia populations.     

Migratory patterns of lower Feather River natural and hatchery-origin Oncorhynchus mykiss

Oncorhynchus mykiss are known to exhibit variable life histories expressed under genetic control or through the influence of the environment. Altered environmental conditions and the presence of large numbers of non-indigenous hatchery fish can affect the rate of anadromy observed in California’s Central Valley O. mykiss. The lower Feather River, a large regulated river in Northern California, supports one of the largest populations of O. mykiss in the Central Valley, heavily subsidized by hatchery production. I examined downstream migratory behavior, movement rate, and success of natural-origin juveniles, natural-origin adults, and hatchery-origin fish using acoustic telemetry. I found that all three groups displayed a mix of migratory and non-migratory life histories. Hatchery-origin adults exhibited more migratory behavior (anadromy) than natural-origin juveniles and natural-origin adults, 41 %, 24 %, and 13 % respectively. Downstream migrants were also significantly larger than non-migratory fish. Migration timing was similar among the three groups, but natural-origin juveniles displayed the most rapid rate of movement. The relative success of each group was highest for fish migrating through the Sacramento-San Joaquin Delta to the Pacific Ocean. Hatchery-origin adults migrating through the lower Feather River showed the lowest relative success (33 %). The dominance of non-migratory life histories pattern among lower Feather River O. mykiss may be in response to the suitable habitat provided by hypolimnetic releases below dams and the current hydrological regime within the highly altered Sacramento-San Joaquin watershed.     

Understanding the effects of isolation on seed and pollen flow,spatial genetic structure and effective population size of the dioecious tropical tree species <Emphasis Type="Italic">Myracrodruon urundeuva</Emphasis>

This study examines the levels of gene flow, the distance and the patterns of pollen and seed dispersal, the intra-population spatial genetic structure (SGS) and the effective population size of a spatially isolated Myracrodruon urundeuva population using five microsatellite loci. The study was carried out in the Paulo de Faria Ecological Station, São Paulo State, Brazil and included the sampling and mapping of 467 adult-trees and 149 juveniles. Open-pollinated seeds (514) from 29 seed-trees were also sampled and genotyped. Significant SGS was detected in both adult (S _p  = 0.0269) and juveniles trees (S _p  = 0.0246), indicating short-distance seed dispersal. Using maternity analysis, all juveniles had the mother-tree assigned within the stand. A father-tree within the stand was also assigned for 97.3% of the juveniles and 98.4% of offspring. The average pollen dispersal distance measured in juveniles \( \left( {\hat{\delta } = 1 3 8\pm 1 6 9 {\text{ m}},{\text{ mean}} \pm {\text{SD}}} \right) \) and offspring \( \left( {\hat{\delta } = 2 5 2\pm 20 4 {\text{ m}}} \right) \) were higher than the average seed dispersal distance measured in juveniles \( \left( {\hat{\delta } = 1 2 4\pm 1 50{\text{ m}}} \right) \). About 70% of the pollen from juveniles and 51% from offspring traveled less than 200 m and, 72% of the seeds traveled less than 50 m. The effective population size of the studied sample indicates that the 467 adult-trees and 145 juveniles correspond respectively to 335 and 63 individuals that are neither inbred nor relatives. The results are discussed in relation to their impact on seed collection practices and genetic conservation.     

Ontogenetic diet shift in Commerson’s dolphin (Cephalorhynchus commersonii commersonii) off Tierra del Fuego

The Commerson’s dolphin (Cephalorhynchus c. commersonii, Lacépède, 1804) is the most common endemic dolphin of the coastal waters of Tierra del Fuego incidentally caught in artisanal coastal gill nets. A better understanding of its trophic ecology is essential to facilitate the effective management and conservation of its population. The aim of this study was to analyze possible shifts in diet among age and sex classes by analyzing bone collagen δ¹³C and δ¹⁵N values collected from 220 individuals along the coast of Tierra del Fuego. Additional analysis of potential prey allowed us to use a stable isotope mixing model to quantify resource use. Isotopic comparisons suggest that all age classes share the same foraging areas. We found, however, a significant dietary shift: juveniles consume a higher mean (±SD) proportion (60 ± 7 %) of pelagic Sprattus fuegensis than adults (36 ± 10 %), and the consumption of benthopelagic species such as Illex argentinus and Loligo gahi is higher in adults (33 ± 12 %) than juveniles (20 ± 7 %). This may result from an improvement in foraging skills and expansion of habitats in adulthood. While males move greater distances in search of mates and resources, a lack of isotopic differences between the sexes suggests little evidence for sex-related resource partitioning. A significant decrease in δ¹⁵N values between calves and juveniles indicates a weaning period between 0.5 and 1 year as was shown in previous captive studies on this species. Our results also suggest that artisanal fisheries, despite being a major source of mortality, do not affect the long-term food habits of Commerson’s dolphin since they showed a weak trophic overlap.     

Sequence and expression of an α-amylase gene in four related species of prickleback fishes (Teleostei: Stichaeidae): ontogenetic,dietary, and species-level effects

Partial α-amylase gene sequences were determined and α-amylase gene expression was quantified in four species of carnivorous, omnivorous, and herbivorous prickleback fishes (family Stichaeidae) to assess the effects of ontogeny, diet, and species on expression of this gene. Pairwise comparison of α-amylase nucleotide sequences revealed 96–98 % identity, and comparison of amino acid portions revealed 93–95 % similarity among the four prickleback species. Expression was determined using in situ hybridization and intensity of expression quantified using image analysis. Alpha-amylase expression level was compared in three feeding categories of the four species: (1) small, wild-caught carnivorous juveniles; (2) larger, wild-caught juveniles of the carnivorous species and the three that had shifted to herbivory or omnivory; and (3) larger, juveniles produced by feeding a low-starch artificial diet to small juveniles until they reached the size of the larger wild-caught juveniles. The results showed no dietary effect in any species but significant ontogenetic and species-level effects in Cebidichthys violaceus, as well as in the sister species Xiphister mucosus and X. atropurpureus. Based on a phylogeny for the Stichaeidae produced for this study using two mtDNA genes and one nuclear gene, the ontogenetic dietary shifts to herbivory/omnivory evolved independently in C. violaceus and in the clade containing the two species of Xiphister. All three of these species increased α-amylase gene expression with increase in size and had higher expression than Anoplarchus purpurescens, which is a member of a third, stichaeid clade comprising carnivores. These results show the importance of α-amylase in the herbivores and omnivores.     

Gastrodin Ameliorates Memory Deficits in 3,3′-Iminodipropionitrile-Induced Rats: Possible Involvement of Dopaminergic System

3,3′-Iminodipropionitrile (IDPN), one of the nitrile derivatives, can induce neurotoxicity, and therefore cause motor dysfunction and cognitive deficits. Gastrodin is a main bioactive constituent of a Chinese herbal medicine (Gastrodia elata Blume) widely used for treating various neurological disorders and showed greatly improved mental function. This study was designed to determine whether administration of gastrodin attenuates IDPN-induced working memory deficits in Y-maze task, and to explore the underlying mechanisms. Results showed that exposure to IDPN (150 mg/kg/day, v.o.) significantly impaired working memory and that long-term gastrodin (200 mg/kg/day, v.o.) could effectively rescue these IDPN-induced memory impairments as indicated by increased spontaneous alternation in the Y-maze test. Additionally, gastrodin treatment prevented IDPN-induced reductions of dopamine (DA) and its metabolites, as well as elevation of dopamine turnover ratio (DOPAC + HVA)/DA. Gastrodin treatment also prevented alterations in dopamine D2 receptor and dopamine transporter protein levels in the rat hippocampus. Our results suggest that long-term gastrodin treatment may have potential therapeutic values for IDPN-induced cognitive impairments, which was mediated, in part, by normalizing the dopaminergic system.     

Size and experience matter: diving behaviour of juvenile New Zealand sea lions (Phocarctos hookeri)

The diving ability of juvenile animals is constrained by their physiology, morphology and lack of experience, compared to adults. We studied the influences of age and mass on the diving behaviour of juvenile (2–3-year-old females, n = 12; 3–5-year-old males, n = 7) New Zealand (NZ) sea lions (Phocarctos hookeri) using time–depth recorders (TDRs) from 2008 to 2010 in the NZ subantarctic Auckland Islands. Diving ability (e.g. dive depth, duration and bottom time per dive) improved with age and mass. However, the percentage of each dive spent at the bottom, along with percentage time at sea spent diving, was comparable between younger and lighter juveniles and older and heavier juveniles. These suggest that younger and older juveniles expend similar foraging effort in terms of the amount of time spent underwater. Only, 5-year-old male juveniles dove to adult female depths and durations and had the highest foraging efficiency at depths >250 m. It appears that juvenile NZ sea lions attain adult female diving ability at around 5 years of age (at least in males), but prior to this, their performance is limited. Overall, the restricted diving capabilities of juvenile NZ sea lions may limit their available foraging habitat and ability to acquire food at deeper depths. The lower diving ability of juvenile NZ sea lions compared to adults, along with juvenile-specific constraints, should be taken into consideration for the effective management of this declining, nationally critical species.     

Presettlement schooling behaviour of a priacanthid,the Purplespotted Bigeye Priacanthus tayenus (Priacanthidae: Teleostei)

We report in situ behavioural observations of presettlement schooling in Priacanthus tayenus off Coral Bay, Western Australia collected using pelagic Baited Remote Underwater stereo-Video systems. Two groups of fish (8 and 9 individuals) were observed that aggregated into a single school. Mean total length was 24.1 mm (12.5–30.2 mm). The fish swam at a mean speed of 8.5 cm s^?1 in a group spacing themselves more or less evenly at a distance of around one body length from the nearest neighbour within the school. P. tayenus appeared to be sometimes associated with juveniles of other species. The results presented here add to the limited, but growing body of literature on the schooling behaviour of the early pelagic stages of demersal fishes.     

Characterization of a novel β-agarase from an agar-degrading bacterium Catenovulum sp. X3

An agar-degrading bacterium, Catenovulum sp. X3, was isolated from the seawater of Shantou, China. A novel β-agarase gene agaXa was cloned from the strain Catenovulum sp. X3. The gene agaXa consists of 1,590 bp and encodes a protein of 529 amino acids, with only 40 % amino acid sequence identity with known agarases. AgaXa should belong to the glycoside hydrolase family GH118 based on the amino acid sequence similarity. The molecular mass of the recombinant AgaXa (rAgaXa) was estimated to be 52 kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. It had a maximal agarase activity at 52 °C and pH 7.4 and was stable over pH 5.0?~?9.0 and at temperatures below 42 °C. The K _m and V _max for agarose were 10.5 mg/ml and 588.2 U/mg, respectively. The purified rAgaXa showed endolytic activity on agarose degradation, yielding neoagarohexaose, neoagarooctaose, neoagarodecaose, and neoagarododecaose as the end products. The results showed that AgaXa has potential applications in agar degradation for the production of oligosaccharides with various bioactivities.     

Recruitment bottlenecks in the rare Australian conifer Wollemia nobilis

Seedling survival plays a critical role in maintaining a supply of potential recruits. We examined seedling recruitment, survival and growth in Wollemia nobilis, a rare, long-lived Australian conifer. Wollemia nobilis seedlings and juveniles were monitored for 16 years (1996–2011). While W. nobilis can recruit from seed and, unlike most conifers, persist through resprouting, seed-based recruitment was the primary focus of this study. Sixty-five per cent of new seedlings died within their first year and only 7 % persisted for the 16-year monitoring period. However, 44 % of established juvenile plants (of unknown age at the beginning of the study) persisted throughout the 16-year monitoring period. Growth of seedlings and juveniles was very slow; growth estimates for most individuals had 95 % confidence intervals that included zero. The recruitment strategy of W. nobilis may be to maintain a slow-growing juvenile bank—a strategy typical of other shade-tolerant rainforest trees, including other Araucariaceae. Seedling recruitment in W. nobilis may act together with resprouting to maintain the population.     

Reproductive biology of the invasive Asian freshwater leech Barbronia weberi (Blanchard, 1897)

Barbronia weberi were collected from Hydrilla verticillata purchased from aquarium suppliers in Melbourne, Australia and additional B. weberi were obtained from aquatic plants in Canberra, ACT, Australia. Adult leeches fed Tubifex sp. ad libitum successfully reproduced under laboratory conditions (21 ± 5?°C ). Reproductively mature B. weberi produced cocoons every week for up to three months at which time the adults began to senesce. Cocoons contained one to five (barx=2.41±0.78 SD, N=58) eggs with juveniles leaving the cocoon within 27 ± 3.4 SD days (N=13) of cocoon production. Juvenile B. weberi reached reproductive maturity within four months (N=7) of hatching and had a maximum growth rate of 1.10 mm² d^?1 once they left the cocoon at around 30 days. Individual egg volume (r=0.63, scaling exponent = 1.21) and cocoon volume (r=0.65, scaling exponent = 1.24) showed a significant (P<0.001) and nearly isometric relationship when scaled with maternal body size. Because this species can grow rapidly and produce a large number of eggs over a short period of time and can piggyback with plant species and travel through the aquarium trade, there is potential for B. weberi to rapidly invade new localities.     

An Efficient Protocol for Ulmus minor Mill. Protoplast Isolation and Culture in Agarose Droplets

We describe here an efficient and reproducible protocol for isolation and culture of protoplasts from Ulmus minor. Different sources of donor tissues were tested for protoplast isolation: callus and juvenile leaves from in vitro and greenhouse plants. Several combinations and concentrations of hydrolytic enzymes were used. Comparative tests between Cellulase Onozuka R10 and Cellulase Onozuka RS were made and the last one proved to be more efficient. Both the pectinases used, Macerozyme Onozuka R10 and Pectinase (Sigma^®), were efficient in protoplast isolation and there was no need for a more active pectinase. In vitro leaves proved to be the best source for protoplast isolation and produced an average of 3.96 × 10⁷ protoplasts per gram of fresh weigh. Elm mesophyll protoplasts were cultured using the advantageous method of agarose droplets and a modification of the Kao and Michayluk culture medium, using two plating densities (1 × 10⁵ and 2 × 10⁵ protoplasts ml^?1). Protoplast division and evolution into colonies and microcalli was promoted in the agarose droplets plated at 2 × 10⁵ protoplasts ml^?1. Ten weeks after protoplast culture initiation a plating efficiency of 2.7% was attained and the bigger microcalli, with at least 0.5 mm diameter, were transferred to a solid medium previously used for the production of embryogenic callus.     

Observation of protein folding/unfolding dynamics of ubiquitin trapped in agarose gel by single-molecule FRET

A ubiquitin mutant with two Cys mutations, m[C]q/S65C, was site-specifically labeled with two dye molecules, Alexa Fluor 488 (donor) and Alexa Fluor 594 (acceptor), due to the different reactivity of these two Cys residues. This doubly dye-labeled ubiquitin has lower structural stability than wild-type ubiquitin. Taking advantage of this decreased stability, conformational heterogeneity of this protein under nondenaturing condition was observed at the single-molecule level using single-paired Förster resonance energy transfer (FRET) by trapping the protein in agarose gel. Three conformational populations corresponding to folded (E _ET ≈ 0.95), loosely packed (E _ET ≈ 0.72), and unfolded (E _ET ≈ 0.22) structures, and the structural transitions between them were observed. Our results suggest that agarose immobilization is good for observing structural dynamics of proteins under native condition.     

The IMTA-cultivated Chlorophyta Ulva spp. as a sustainable ingredient in Nile tilapia (Oreochromis niloticus) diets

Increasing levels of a mixture of Ulva spp. produced in an integrated multi-trophic aquaculture (IMTA) system were evaluated in Nile tilapia juveniles for partial replacement of dietary fish meal. A control diet (CTRL) was compared with three experimental diets containing 10 % (U10), 15 % (U15), and 20 % (U20) of Ulva spp. meal. Triplicate groups of fish (13 g initial body weight) were fed each diet for 63 days at 26 °C. Nutrient apparent digestibility coefficients and nitrogen retention efficiency did not vary significantly among diets. By the end of the trial, all groups of fish more than tripled their initial body weight. Specific growth rate and final body weight of U10 diet were similar to CTRL and significantly higher than U15 and U20 diets. Increasing Ulva dietary incorporation levels significantly increased feed conversion ratio (FCR), from 1.0 (CTRL) to 1.4 (U20). Fish fed with U10 diet had the highest protein efficiency ratio and nitrogen retention efficiency allowing this fish to growth and reach a final body weight similar to the CTRL group. Protein content was highest in fish fed with the CTRL diet, whereas the highest lipid content was observed in fish fed with U20 diet. The results show that the incorporation of IMTA-produced Ulva meal in Nile tilapia diets is possible up to 10 % without compromising growth performance, protein utilization, and protein retention of juveniles. The high capacity of Nile tilapia to digest all experimental diets suggests that Ulva meal is a practical partial replacement for fish meal in Nile tilapia diets.