Tuna Larvae Research Articles

Misidentification of bluefin tuna larvae: a call for caution and taxonomic reform

The international effort to prevent the collapse of Atlantic bluefin tuna (BFT, Thunnus thynnus, Scombridae) stocks exemplifies the challenges associated with modern marine resource conservation. Rampant mismanagement, under-reporting and illegal, unreported and unregulated fishing led to decades of over-exploitation in the BFT fishery. Surveys of larval abundance in the Gulf of Mexico and the Mediterranean Sea have been used as a proxy for both spawning biomass and recruitment by researchers working to improve estimates of stock abundance. Recent genetic barcoding studies have revealed that species identification errors are common among larvae surveys that use morphology-based taxonomy alone. Misidentification of larvae can lead to uncertainty about the spatial distribution of a species, confusion over life history traits and population dynamics, and potentially disguise the collapse or recovery of localized spawning sites. In an effort to identify the source of these errors, we review several weaknesses in modern morphology-based taxonomy including demographic decline of expert taxonomists, flawed identification keys, reluctance of the taxonomic community to embrace advances in digital communications and a general scarcity of modern user-friendly materials. Recent advances in molecular techniques useful for specimen identification and population studies are discussed at length. We advocate a more constructive integration of morphology-based taxonomy and barcoding in order to add confidence to larval surveys and to strengthen associated fisheries management.

Prey selectivity in piscivorous bluefin tuna larvae reared in the laboratory

Prey size selectivity in piscivorous fish larvae is important to both aquaculture and fisheries science, but laboratory experiments are few. We analyzed selective foraging in Atlantic bluefin tuna larvae ( Thunnus thynnus) using two larval fish prey species. The experiments revealed that selective foraging of prey sizes differed among bluefin tuna predator sizes (15–25 mm SL) and prey species, bonito ( S arda sarda ) and seabream ( Sparus aurata ). The observed pattern suggest a general preference for small bonito prey larvae but large seabream prey. Thus, prey size alone is not the only trait responsible for size selectivity in piscivorous fish larvae.

Differential growth rates related to initiation of piscivory by hatchery-reared larval Pacific bluefin tuna Thunnus orientalis

Fast growth plays an important role in survival processes during the early life stages of both field-captured and hatchery-reared Pacific bluefin tuna Thunnus orientalis. Marked growth variations in hatchery-reared tuna larvae are frequently observed even for the same age and within the same rearing tank after the onset of the piscivory. We hypothesized that these small growth variations in the growth of tuna larvae at the onset of piscivory lead subsequently to large growth variations and tested the hypothesis using three size groups (large, intermediate and small) of hatchery-reared fish by nitrogen stable isotope and otolith analyses. Stable isotope analysis revealed that the large group rapidly utilized prey fish larvae, but the smaller groups depended more on rotifers as the main prey item relative to the large group. The otolith radius from the core to the increment corresponding to the first feeding on yolk-sac larvae was compared among the three size groups. The results revealed that the large group had larger otolith radii than the small and intermediate groups. Our findings suggest that small growth variations apparent during the early larval stage of tuna could induce further large growth variations in the late-larval and juvenile stages through differences in the initial ability to utilize piscivory.

Characterization and ontogenetic development of digestive enzymes in Pacific bluefin tuna Thunnus orientalis larvae.

The major digestive enzymes in Pacific bluefin tuna Thunnus orientalis larvae were characterized, and the physiological characteristics of the enzymes during early ontogeny were clarified using biochemical and molecular approaches. The maximum activity of trypsin (Try), chymotrypsin (Ct) and amylase (Amy) was observed at pH 6-11, 8-11 and 6-9, respectively. Maximum activity of Try, Ct and Amy occurred at 50 °C, that of lipase (Lip) was at 60 °C and that of pepsin (Pep) was at 40-50 °C. These pH and thermal profiles were similar to those for other fish species but differed from those previously reported for adult bluefin tuna. Enzyme activity for all enzymes assayed was found to decrease at high temperatures (Try, Ct, Amy and Pep: 50 °C; Lip: 40 °C), which is similar to findings for other fish species with one marked exception-increased Try activity was observed at 40 °C. Lip activity appeared to be dependent on bile salts under our assay conditions, resulting in a significant increase in activity in the presence of bile salts. Ontogenetic changes in pancreatic digestive enzymes showed similar gene expression patterns to those of other fish species, whereas marked temporal increases in enzyme activities were observed at 10-12 days post hatching (dph), coinciding with previously reported timing of the development of the pyloric caeca in bluefin tuna larvae. However, complete development of digestive function was indicated by the high pep gene expression from 19 dph, which contradicts the profile of Pep activity and previously reported development timing of the gastric gland. These findings contribute to the general knowledge of bluefin tuna larval digestive system development.

Worldwide distributions of tuna larvae: revisiting hypotheses on environmental requirements for spawning habitats

Instituto Espanol de Oceanografia, Centre Oceanografic de les Balears, Moll de Ponent s/n, 07015 Palma de Mallorca, Spain United Nations Environment Programme World Conservation Monitoring Centre, Cambridge CB3 0DL, UK Microsoft Research Computational Science Laboratory, Cambridge CB3 0FB, UK Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax B3H 4R2, Canada SOCIB, Balearic Islands Coastal Observing and Forecasting System, Palma de Mallorca, Spain

Organogenesis of digestive system, visual system and other structures in Atlantic bluefin tuna (Thunnus thynnus) larvae reared with copepods in mesocosm system

Abstract This study examines the anatomical development of Atlantic bluefin tuna during the first month of life at histological level with emphasis in the gut development and those organs required to establish the hunting behaviour characteristic of this species. The tuna larvae have been reared in mesocosm with copepods ( Acartia and Trigriopus sp.) as primary live prey during the first two weeks. The larvae hatched with 3.4 mm average TL and exhibited a very fast growth reaching between 4 and 5 cm at the end of the first month. The yolk reserves were consumed rapidly in two days. As an altricial species the gut and most of the sensory organs were not developed at hatching. The transformation of the gut from an undifferentiated canal at hatching up to a complex and segmented juvenile-like digestive tract occurred in three weeks. At hatching, the digestive tract appeared as a straight tube dorsal to the yolk-sac. The opening of both mouth and anus occurred at 2 days post-hatching (dph). From 4 dph onwards, intestinal loops started to be visible and the primordial future stomach started to develop. Intestinal brush border and increased folds in length were detected in the intestine from 4 dph. Acidophilic protein supranuclear inclusions within the hindgut enterocytes and the first signs of lipid absorption within enterocytes of the anterior intestine were evident from 6 dph. First gastric glands were detected at 11 dph, and at 17 dph the stomach was practically developed with the apparition of the first pyloric caeca. Newly hatched Atlantic bluefin tuna larvae had unpigmented eyes. The eyes were pigmented and functional at the opening of the mouth (between 2 and 3 dph), and rods appeared at 17 dph. Nevertheless twin cones were not observed during the first month. The bluefin tuna larvae quickly acquired a degree of development that allows for efficient predation and digestion of more complex feeds. In fact, the digestive system, sensory and visual structures, thyroid gland, swim bladder, and the kidney and heart differentiated very early during the larval ontogeny of this species, and they were well developed and practically fully functional around 17–18 dph under our rearing conditions. At 21 dph with the change in the allometry of mouth size the post-larvae exhibited most of the juvenile anatomical characteristics.

Gene expression pattern of digestive and antioxidant enzymes during the larval development of reared Atlantic bluefin tuna (ABFT),Thunnus thynnusL.

The aim of this study was to determine whether mortality observed during the larval development of reared bluefin tuna (Thunnus thynnus) could be related to improper expression profiles of key genes involved in digestive or antioxidant response capabilities. Tuna larvae were sampled at hatching, 2, 5, 10, 15 and 20 dph (days post hatching) for the relative quantification of transcripts encoded by genes involved in digestive [trypsinogen 1 (TRYP1), alpha‐amylase (AMY), aminopeptidase N (ANPEP)] and antioxidant [catalase (CAT)] functions. The levels of expression of ANPEP related to the development and maturation of intestinal function increased from 5 to 20 dph. Furthermore, AMY and TRYP1 genes, which are pancreatic enzymes implicated in carbohydrate and peptide digestions exhibit a typical peak of expression at 5 and 15 dph respectively. The antioxidant enzyme, CAT, exhibited higher mRNA levels during the first stage of larval development. In conclusion, our investigation indicates that the expression of genes involved in digestive and antioxidant physiological processes followed typical patterns which could not explain high mortality rate observed during the first stage of larval development.

Spatial distribution of tuna larvae in the Gulf of Gabes (Eastern Mediterranean) in relation with environmental parameters

Spatial distribution and ecology of the larvae of three tuna species (Thunnus thynnus, Auxis rochei and Euthynnus alletteratus) were studied during an ichthyoplankton survey carried out in the Gulf of Gabes (Tunisia) in June and July 2009. A total of 80 stations, distributed on a regular sampling grid, were sampled. The main objectives of this survey were to provide information on tuna larvae distribution in the Gulf of Gabes in relation to the environmental parameters. Regarding small tunas, larvae of A. rochei (bullet tuna) showed the more widespread distribution, being found at both inshore and offshore stations. E. alletteratus (Atlantic black skipjack) larvae were mainly found at the inshore stations covering the wide continental shelf of this region. On the other hand, larvae of the large migratory tuna T. Thynnus (Atlantic bluefin tuna), were mainly recorded at offshore stations, suggesting that spawning possibly takes place mainly near the shelf break. Regarding the biological and physical parameters examined, our results indicate that tuna larvae were mainly collected in oligotrophic and mixed waters resulting from the confluence of surface water of recent Atlantic origin and resident surface Mediterranean waters, as shown by their preference for lower chlorophyll a concentrations (from 1.4 to 2.5 mg m-3) and moderate salinity values (between 37.35 and 37.75). Significantly, tuna larvae seemed to avoid the more eutrophic and saltier waters of the gulf situated very close to the coast and around Kerkennah and Djerba islands.

Otolith δ18O of Pacific bluefin tuna Thunnus orientalis as an indicator of ambient water temperature

To detect the relationship between ambient temperature and otolith stable oxygen isotope (δ18O), Pacific bluefin tuna Thunnus orientalis larvae were reared at 6 different temperatures (between 23 and 28°C at 35 psu; mean δ18O value, +0.31‰) for 2 to 8 d after hatching. For the first time, otolith δ18O was measured using a continuous-flow isotope ratio mass spectrometry system. The linear relationship between otolith δ18O and temperature was determined as follows: δotolith – δwater = –2.70 (T °C) + 5.193 (r2 = 0.806, p < 0.01). The temperature-dependent fractionation of otolith δ18O was close to that reported for inorganic aragonite, indicating that the vital effects of isotopes are small. The otolith δ18O values of juveniles reared at a mean of 26.5°C were not significantly different from those of larvae reared at 26°C. With regard to the 2 pairs of otoliths within an individual fish, the differences in δ18O values between the left and right otoliths were subtle. The otolith δ18O values of larvae reared in δ18O-depleted seawater (24 to 26°C at 32 psu; δ18O, −0.17‰) were lower, but were not significantly different from those of larvae reared in +0.31‰ water, which is the δ18O value of the water in which the spawners were raised. These results suggest that the sample size for the 32 psu experiment was too small and that the rearing durations were too short to affect the otoliths completely. Our results demonstrate that otolith δ18O values of Pacific bluefin tuna larvae can provide precise and accurate estimates of their ambient temperature experience.

Spatial distribution of tuna larvae in the Gulf of Gabes (Eastern Mediterranean) in relation with environmental parameters

Spatial distribution and ecology of the larvae of three tuna species (Thunnus thynnus, Auxis rochei and Euthynnus alletteratus) were studied during an ichthyoplankton survey carried out in the Gulf of Gabes (Tunisia) in June and July 2009. A total of 80 stations, distributed on a regular sampling grid, were sampled. The main objectives of this survey were to provide information on tuna larvae distribution in the Gulf of Gabes in relation to the environmental parameters. Regarding small tunas, larvae of A. rochei (bullet tuna) showed the more widespread distribution, being found at both inshore and offshore stations. E. alletteratus (Atlantic black skipjack) larvae were mainly found at the inshore stations covering the wide continental shelf of this region. On the other hand, larvae of the large migratory tuna T. Thynnus (Atlantic bluefin tuna), were mainly recorded at offshore stations, suggesting that spawning possibly takes place mainly near the shelf break. Regarding the biological and physical parameters examined, our results indicate that tuna larvae were mainly collected in oligotrophic and mixed waters resulting from the confluence of surface water of recent Atlantic origin and resident surface Mediterranean waters, as shown by their preference for lower chlorophyll a concentrations (from 1.4 to 2.5 mg m-3) and moderate salinity values (between 37.35 and 37.75). Significantly, tuna larvae seemed to avoid the more eutrophic and saltier waters of the gulf situated very close to the coast and around Kerkennah and Djerba islands.

Prey Utilization by Hatchery-reared Pacific Bluefin Tuna Larvae in Mass Culture Tank Estimated Using Stable Isotope Analysis, with Special Reference to Their Growth Variation

Prey Utilization by Hatchery-reared Pacific Bluefin Tuna Larvae in Mass Culture Tank Estimated Using Stable Isotope Analysis, with Special Reference to Their Growth Variation

Relationship between prey utilization and growth variation in hatchery-reared Pacific bluefin tuna,Thunnus orientalis(Temminck et Schlegel), larvae estimated using nitrogen stable isotope analysis

In mass culture of Pacific bluefin tuna Thunnus orientalis, a marked growth variation is observed after they start feeding at 6–7 mm in body length (BL) on yolk-sac larvae of other species, and the growth variation in tuna larvae is a factor leading to the prevalence of cannibalism. To examine the relationship between prey utilization and growth variation, nitrogen stable isotope ratios (δ15N) of individual larvae were analysed. A prey switch experiment was conducted under two different feeding regimes: a group fed rotifers (rotifer fed group), and a group fed yolk-sac larvae of spangled emperor, Lethrinus nebulosus (fish fed group) from 15 days after hatching (6.87 mm BL). The fish fed group showed significantly higher growth than the rotifer fed group. Changes in the δ15N of the fish fed group were expressed as an exponential model and showed different patterns from those of the rotifer fed group. The δ15N of fast-growing tuna larvae collected in an actual mass culture tank after the feeding of yolk-sac larvae was significantly higher than those of the slow-growing larvae, indicating that slow glowing larvae depended largely on rotifers rather than the yolk-sac larvae.

A spatiotemporal study of bacterial community profiles associated with Atlantic bluefin tuna larvae,Thunnus thynnusL., in three Mediterranean hatcheries

During the first 2 years of larval rearing trials with Atlantic bluefin tuna, survival was a challenging issue. As bacterial colonization of the gut has been shown to play a key role for other species, we studied the profiles of the microbiota associated with individual larvae at different stages in three distant hatcheries. The Bacterial Community Profile (BCP) was quantified based on PCR-DGGE analyses of partial amplicons from 16S rDNA. Considerable individual variability in BCP was observed before onset of feeding, and the BCP did not show regular fluctuation during ontogenesis. Microalgae were added to the rearing tanks in two of the three hatcheries, but it was not possible to distinguish the effect of location from the effect of algal addition on BCP. In one hatchery, the larvae were reared either with algal addition or in mesocosm, but due to high individual variability, no significant difference in BCP was detected between the two groups. It was hypothesized that this variability was caused by differences in health, physiological status and developmental stage of the larvae. A practical conclusion from the study is the need to analyse a considerable number of individuals to reflect statistically significant differences between the microbial communities associated with rearing groups.

Onset of individual growth difference in larviculture of Pacific bluefin tuna Thunnus orientalis using fertilized eggs obtained from one female

We conducted a rearing experiment on Pacific bluefin tuna (PBT) larvae, which originated from one female broodstock, and determined the growth history of the larvae to clarify when the growth difference occurs. We investigated the otolith microstructure of the PBT larvae to examine the individual growth history and to predict the age and body size at the onset of individual growth difference. Since total length (TL) of fish can be back-calculated from otolith radius, we back-calculated TLs of 100 fish of 19 days post hatch (dph) divided into three size groups (small, intermediate, large). Growth difference was recognized from 3 dph (mouth opening), and the difference became larger thereafter. Growth of large-size fish was assumed to be promoted by the feeding conditions of PBT larvae.

Enhancement of survival rate of Pacific bluefin tuna (Thunnus orientalis) larvae by aeration control in rearing tank

High levels of larval mortality are a significant barrier to the artificial mass production of Pacific bluefin tuna (Thunnus orientalis ). Mortality may occur when larvae sink and come into contact with the bottom of the rearing tank during the first 10 days after hatching. We evaluated the effect of flow control by aeration on the survival of T. orientalis larvae. These larvae were held in 500-L tanks in which the aeration rate was varied during the night. Larval survival increased with air supply. We documented the cross-sectional flow pattern and gravitational sinking velocities of larvae to assess the correlation between survival and circulation patterns in the tank. The sinking velocity of T. orientalis larvae at night increased with larval body density, which varied with swimbladder volume. Larvae with uninflated swimbladders sank significantly faster than larvae with inflated swimbladders. Both water circulation speed and survival increased at higher aeration rates. Our results suggest that aeration rates >900 ml min–1 may increase larval survival by counteracting sinking.

Coexistence of larvae of tuna species and other fish in the surface mixed layer in the NW Mediterranean

To analyze the potential trophic interactions among tuna larvae and other fish species, we studied the larval fish assemblages inhabiting the surface mixed layer around the Balearic Islands using data from two surveys carried out in summer 2006 and 2008. Despite the high diversity, Thunnus alalunga, Auxis rochei, Cyclothone pygmaea and Ceratoscopelus maderensis clearly dominated the catch in both years. The spatial distribution of several larval fish assemblages, in which tuna larvae were among the dominant species, was related to the presence of fronts and mixed Atlantic waters (AW). Different developmental stages of tuna were found in similar hydrographical scenarios. Smaller tuna larvae and plausible piscivorous tuna were found in the areas with mixed AW. Later in the season, potential piscivorous tuna were found together with small larvae from other non-tuna species that had been spawned later and transported by the fresh AW flow to offshore stations. That the different life stages of tuna co-occur with mesopelagic species in the mixed layer reveals the interesting possibility of ecological interactions between the different larvae.

Cannibalism among size classes of larvae may be a substantial mortality component in tuna

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 433:205-219 (2011) - DOI: https://doi.org/10.3354/meps09187 Cannibalism among size classes of larvae may be a substantial mortality component in tuna P. Reglero1,*, A. Urtizberea2, A. P. Torres1, F. Alemany1, Ø. Fiksen2, 3 1Instituto Español de Oceanografía, Centre Oceanogràfic de les Balears, Moll de Ponent s/n, 07015 Palma, Spain2Department of Biology, University of Bergen, PO Box 7803, 5020 Bergen, Norway3Uni Research, PO Box 7810, 5020 Bergen, Norway *Email: patricia.reglero@ba.ieo.es ABSTRACT: Cannibalism among size classes may reduce starvation and improve survival of larval tuna in oligotrophic ocean areas, but it may also be a substantial mortality component depending onthe availability of alternative prey. Here, we combine laboratory and field data on tuna larvae with amodel of larval foraging and bioenergetics to explore the role of cannibalism in cohort developmentat different temperatures, durations of hatching period, hatching larval densities and natural mortalityrates. Prey fields (zooplankton densities and co-occurrence of different larval stages of 3 species of tuna) were established from cruises in a main tuna spawning area around the Balearic Islands (Mediterranean Sea). Results suggest that a pure zooplankton diet is frequently insufficient to sustain larval growth. Piscivory can be a major source of larval mortality among tuna species and larvae hatched early can feed on abundant larvae of smaller size and have fewer predators themselves. We show how the intensity of cannibalism depends on the temperature dependent growth rate and the resulting relative size distribution when eggs are released continuously over a period of a few weeks. The predator-prey size distribution and the relative densities of these voracious larvae may produce overcompensation in recruitment under some environmental conditions. KEY WORDS: Cannibalism · Foraging model · Intraspecific predation · Natural mortality · Pelagic larvae · Predator-prey interactions · Size spectra · Surf-riding Full text in pdf format PreviousNextCite this article as: Reglero P, Urtizberea A, Torres AP, Alemany F, Fiksen Ø (2011) Cannibalism among size classes of larvae may be a substantial mortality component in tuna. Mar Ecol Prog Ser 433:205-219. https://doi.org/10.3354/meps09187 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 433. Online publication date: July 18, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

The effect of a 24-hour photoperiod on the survival, growth and swim bladder inflation of pre-flexion yellowfin tuna ( Thunnus albacares) larvae

The effects of two different continuous photoperiod regimes on survival, growth and swim bladder inflation of pre-flexion yellowfin tuna ( Thunnus albacares) larvae were investigated. Each photoperiod regime was tested twice with a different larval cohort to confirm the observed results. Trials 1 and 2 tested the effect of a reduced night-time light intensity (10 μmoles m − 2 s − 1 = 30% of the daytime intensity) and found that those larvae reared for 8 days under the 24 h lighting (24-L) photoperiod exhibited a slight improvement in survival compared to those reared under the control photoperiod of 12 h light (12-L), however these improvements were not significant. In addition, those larvae reared under this photoperiod regime were equal in length to those in the control. Trials 3 and 4 compared the same variables in larvae reared under a continuous photoperiod (24-L) with a constant light intensity of 30 μmoles m − 2 s − 1 , against those reared under the aforementioned 12-L photoperiod. Survival of larvae under the continuous photoperiods were 9 ± 1% (n = 2) and 10 ± 2% (n = 3) for Trials 3 and 4, respectively, compared to less than 1% in both control treatments; differences that in both cases were highly significant. In addition, in both trials larvae cultured under the 24-L photoperiod were significantly larger and exhibited more advanced development than those reared under the 12-L photoperiod, however swim bladder inflation was significantly lower. We suggest that the improved survival and growth achieved under a continuous photoperiod is due to the extended foraging time combined with the prevention of mortality caused by night-time sinking.

Trophic ecology of Atlantic bluefin tuna Thunnus thynnus larvae

Feeding intensity, diet composition, selectivity, energy ingestion and dietary niche breadth of larval Atlantic bluefin tuna Thunnus thynnus were studied on the eastern (Mediterranean) spawning grounds of the species. Larval T. thynnus were collected in the Balearic Archipelago (north-west Mediterranean Sea) during 2004 and 2005 using surveys specific for larval scombrids. Larvae between 2·6 and 8·7 mm standard length (L(S) ) are diurnal feeders, and 94% of the guts collected during daylight hours were full. The mean ±s.d. number of prey per gut was 7·1 ± 5·7, with mean ±s.d. ranging from 3·0 ± 1·6 in the smallest T. thynnus larvae to 11·1 ± 5·8 in 5·0-6·0 mm L(S) larvae. Up to 21 prey were found in a single larval gut (5·0-6·0 mm L(S) ) at the end of the day. Larvae progressively selected larger prey and exhibited increased carbon content concurrent with preflexion development of feeding and locomotory structures. Larvae of 5·0-6·0 mm L(S) exhibited positive selection of cladocerans over other prey (Chesson's index), whereas copepod nauplii dominated the diets of earlier stages. The dietary niche breadth measured increased initially but decreased at c. 5·5 mm L(S) . Appendicularians were found in the diet of larger larval sizes, but no piscivory was observed. Results are discussed in light of the sparse existing data for larval T. thynnus and other larval tuna species.

Improvement in the feeding activity, early growth and survival of Pacific bluefin tuna Thunnus orientalis larvae fed a casein peptide-based microdiet supplemented with inosine monophosphate

Two feeding experiments were conducted to determine the effect of a 5′-inosine monophosphate (IMP)-supplemented casein peptide-based microdiet (MD) on the feeding activity, growth and survival of Pacific bluefin tuna (PBT) larvae. PBT larvae [total length: 14.0 mm (Exp. 1) or 13.3 mm (Exp. 2)] were fed a casein peptide-based MD supplemented with or without 3% IMP for 12 days. As a negative control, a limited number of yolk-sac larvae of spangled emperor Lethrinus nebulosus were fed only for the first 7 days and starved for the next 5 days. A sufficient amount of yolk-sac larvae of spangled emperor was fed in the Exp. 2. All fish in the control group had died by 9 or 10 days after the experiment. Extensive mortality was observed in fish fed the MD. The MD was only found in the stomach contents of PBT fed the MD + IMP. Of the fish fed an IMP-supplemented diet, 50% survived for 12 days after the initiation of both feeding experiments. In addition, significantly higher growth than that observed during the first 7 days was seen in the PBT in the IMP treatment after 12 days of the feeding experiment. These results suggest that the supplementation of casein peptide-based MD with IMP could improve the feeding activity, survival and growth performance of PBT.