Age and early life history of juvenile scotia sea icefish, <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis>, from Elephant and the South Shetland Islands

The otolith microstructure of juvenile Scotia Sea icefish (Chaenocephalus aceratus) was analyzed from samples collected around Elephant and South Shetland Islands, with the aim to validate previous annual ageing and to give new insight into its early life history timings. Fish were caught by bottom trawl fishing conducted on the continental shelf between 100 and 500 m depth. To determine the timing and position of the first annulus on sagittal otoliths, microincrements were counted on juvenile otoliths previously aged 1+ year old by counting annuli in sectioned otolith. Assuming that microincrements were laid down daily, age ranged from 406 to 578 days in fish measuring 13–19 cm TL, thus corroborating previous results. The relationship between fish size and otolith size/weight was estimated using the least square linear regression method. The relationship between age and otolith size was also estimated to determine the otolith length in 1-year old fish, which was approximately 1.58 mm. In all samples the otolith core was characterized by an evident strong check, assumed to be laid down at the beginning of exogenous feeding of yolk sac larvae. The yolk sac duration estimated from hatch to the first feeding check was longer than other channichthyids, lasting 29–45 days. Hatching dates were backcalculated from the date of capture using the age estimates, indicating C. aceratus sampled off Elephant and South Shetland Islands hatched over a long period lasting from July to December, with a peak in November. As a result, the potential larval dispersion driven by local oceanographic features is discussed.     

Preliminary assessment of population structure in the mackerel icefish (Champsocephalus gunnari)

The mackerel icefish (Champsocephalus gunnari Lönnberg E (1905) The Fishes of the Swedish South Polar Expedition. Wiss. Ergebnisse Schwedische Südpol- Exped. 1901–1903, vol 5, p 37 is widely distributed south of the Antarctic convergence and over shelf areas surrounding sub-Antarctic Islands. In order to evaluate global population structure in this species, we examined DNA sequence variation in four mitochondrial regions and four nuclear genes in icefish from four locations in the Atlantic Ocean sector and one location in the Indian Ocean. Despite small sample sizes, mitochondrial and nuclear gene data indicated the existence of at least three genetically distinct stocks: Heard Island, South Shetland Islands, and the remaining Atlantic populations (Shag Rocks, South Georgia, and Bouvet Island). The mitochondrial and nuclear SNP markers developed here will be useful for more extensive analyses of population structure in this species.     

The alien false limpet (Siphonaria pectinata) in the Bizerte channel (northern Tunisia): spawning,development and growth under laboratory conditions

Spawning, development and growth of Siphonaria pectinata in the laboratory were studied and described in detail during a one-year study period. Egg ribbons were observed in February, March, April, June, July, August and September, with a peak in number of ribbons per individual in July. On average, individuals laid 9.0 ± 5.1 egg ribbons at a spawning frequency of one egg ribbon day^?1. The number of eggs per ribbon ranged from 752 to 50,400 depending on ribbon length. Embryonic development studied in February (13–15 °C), April (15–17 °C) and July (25–27 °C), reached hatching within 8–16 days with average larval lengths of 76.7 ± 5.9, 83.0 ± 11.3 and 78.3 ± 9.0 μm, respectively. Massive mortality was registered a few days after hatching, with larval longevity depending on the study period. Larval settlement occurred within 36–38 days after hatching, but only in the spawn deposited in February. Larval growth was slow during the first three weeks (18–26 μm week^?1) and then accelerated until the sixth week (40–67 μm week^?1). The present study contributes knowledge on the spawning, development and growth of S. pectinata, an alien species recently spreading throughout the Tunisian coast.     

Synchronisation of egg hatching of brown hairstreak (Thecla betulae) and budburst of blackthorn (Prunus spinosa) in a warmer future

Synchronisation of the phenology of insect herbivores and their larval food plant is essential for the herbivores’ fitness. The monophagous brown hairstreak (Thecla betulae) lays its eggs during summer, hibernates as an egg, and hatches in April or May in the Netherlands. Its main larval food plant blackthorn (Prunus spinosa) flowers in early spring, just before the leaves appear. As soon as the Blackthorn opens its buds, and this varies with spring temperatures, food becomes available for the brown hairstreak. However, the suitability of the leaves as food for the young caterpillars is expected to decrease rapidly. Therefore, the timing of egg hatch is an important factor for larval growth. This study evaluates food availability for brown hairstreak at different temperatures. Egg hatch and budburst were monitored from 2004 to 2008 at different sites in the Netherlands. Results showed ample food availability at all monitored temperatures and sites but the degree of synchrony varied strongly with spring temperatures. To further study the effect of temperature on synchronisation, an experiment using normal temperatures of a reference year (T) and temperatures of T + 5°C was carried out in climate chambers. At T + 5°C, both budburst and egg hatch took place about 20 days earlier and thus, on average, elevated temperature did not affect synchrony. However, the total period of budburst was 11 days longer, whereas the period of egg hatching was 3 days shorter. The implications for larval growth by the brown hairstreak under a warmer climate are considered.     

Hatching Time and Alevin Growth Prior to the Onset of Exogenous Feeding in Farmed,Wild and Hybrid Norwegian Atlantic Salmon

The onset of exogenous feeding, when juveniles emerge from the gravel, is a critical event for salmonids where early emergence and large size provide a competitive advantage in the wild. Studying 131 farmed, hybrid and wild Norwegian Atlantic salmon families, originating from four wild populations and two commercial strains, we investigated whether approximately 10 generations of selection for faster growth has also resulted in increased somatic growth prior to the onset of exogenous feeding. In addition, we tested whether relaxed selection in farms has allowed for alterations in hatching time between farmed and wild salmon. Across three cohorts, wild salmon families hatched earlier than farmed salmon families, while hybrid families displayed intermediate hatching times. While the observed differences were small, i.e., 1–15 degree-days (0–3 days, as water temperatures were c. 5–6°C), these data suggest additive genetic variation for hatching time. Alevin length prior to exogenous feeding was positively related to egg size. After removal of egg size effects, no systematic differences in alevin length were observed between the wild and farmed salmon families. While these results indicate additive genetic variation for egg development timing, and wild salmon families consistently hatched earlier than farmed salmon families, these differences were so small they are unlikely to significantly influence early life history competition of farmed and wild salmon in the natural environment. This is especially the case given that the timing of spawning among females can vary by several weeks in some rivers. The general lack of difference in size between farmed and wild alevins, strongly suggest that the documented differences in somatic growth rate between wild and farmed Norwegian Atlantic salmon under hatchery conditions are first detectable after the onset of exogenous feeding.     

Seasonal variations in larval biomass and biochemical composition of brown shrimp, Crangon crangon (Decapoda, Caridea), at hatching

The “brown shrimp”, Crangon crangon (Linnaeus 1758), is a benthic key species in the North Sea ecosystem, supporting an intense commercial fishery. Its reproductive pattern is characterized by a continuous spawning season from mid-winter to early autumn. During this extended period, C. crangon shows significant seasonal variations in egg size and embryonic biomass, which may influence larval quality at hatching. In the present study, we quantified seasonal changes in dry weight (W) and chemical composition (CHN, protein and lipid) of newly hatched larvae of C. crangon. Our data revealed significant variations, with maximum biomass values at the beginning of the hatching season (February–March), a decrease throughout spring (April–May) and a minimum in summer (June–September). While all absolute values of biomass and biochemical constituents per larva showed highly significant differences between months (P < 0.001), CHN, protein and lipid concentrations (expressed as percentage values of dry weight) showed only marginally significant differences (P < 0.05). According to generalized additive models (GAM), key variables of embryonic development exerted significant effects on larval condition at hatching: The larval carbon content (C) was positively correlated with embryonic carbon content shortly after egg-laying (r ² = 0.60; P < 0.001) and negatively with the average incubation temperature during the period of embryonic development (r ² = 0.35; P < 0.001). Additionally, water temperature (r ² = 0.57; P < 0.001) and food availability (phytoplankton C; r ² = 0.39; P < 0.001) at the time of hatching were negatively correlated with larval C content at hatching. In conclusion, “winter larvae” hatching from larger “winter eggs” showed higher initial values of biomass compared to “summer larvae” originating from smaller “summer eggs”. This indicates carry-over effects persisting from the embryonic to the larval phase. Since “winter larvae” are more likely exposed to poor nutritional conditions, intraspecific variability in larval biomass at hatching is interpreted as part of an adaptive reproductive strategy compensating for strong seasonality in plankton production and transitory periods of larval food limitation.     

Hatching patterns and larval growth of a triplefin from central Chile inferred by otolith microstructure analysis

The subtidal rocky reefs are home to a diverse range of marine animals, including small cryptic fishes, characterised by a bipartite life cycle, with benthic adults and pelagic larval stage that lasts from several days to several months. Using the otolith microstructure analysis, this study determines the hatching and larval growth patterns of the abundant triplefin Helcogrammoides chilensis (Pisces: Tripterygiidae). Fish larvae were collected during September–October 2010 and between July 2012 and April 2013 in nearshore waters (<500 m) of central Chile. Nearshore time series of ichthyoplankton samples showed that large abundance of this species occurs during early austral spring and autumn seasons. Body lengths ranged from 3.11 to 16.57 mm (1–57 days old). Sagittal microincrement analyses estimate that during the main reproductive season, larval growth rates are slow, varying between 0.145 and 0.156 mm day^?1 at a weekly scale. Back-calculated hatch days and circular statistics indicate a major hatch pulse occurring near full moon of the lunar cycle. These results suggest that reproduction occurs coupled with the upwelling season, which reduces the probability of starvation, and hatching occurs during spring tides (full moon), which increases larval dispersion and population connectivity.     

First feeding and subsequent growth performances in piscivorous larvae of Chinese perch Siniperca chuatsi (Perciforms: Sinipercidae)

The success of first feeding is influenced by many factors, such as prey availability, and is critical to subsequent larval growth performances. To test the advantages of prey exposure before complete yolk absorption in piscivorous larvae, feeding incidence and specific growth rate were longitudinally measured in Chinese perch Siniperca chuatsi larvae first fed at different ages. The results showed that Chinese perch larvae were able to capture live piscine prey at 4 DAH (days after hatching), 1 day before complete yolk absorption. The feeding incidence and specific growth rate were higher in larvae first fed at 4 DAH than in larvae first fed at 5 or 6 DAH. These results indicate that prey exposure experience can facilitate the onset of first feeding, and that successful exogenous feeding, even before complete yolk absorption, is important for growth performances of piscivorous fish larvae.     

Comparison of early life‐stage strategies in temperate freshwater fish species: trade‐offs are directed towards first feeding of larvae in spring and early summer

Based on the analysis of 12 egg and larval variables and temperature of 65 temperate freshwater fish species, the possible relationships between oocyte diameter, larval size at hatch, time and temperature were reassessed and the main early life‐stage strategies were described and compared. Time and degree‐days required to reach hatching and mixed feeding were weakly related to oocyte diameter and strongly to temperature. These results are chiefly because oocyte diameter and yolk reserves are weakly related and temperature strongly increases tissue differentiation rate, activity of hatching glands and embryo motility. Strong positive relationships were found between larval size and oocyte diameter and degree‐days for incubation. No relationship was found between larval size and degree‐days from hatching to mixed feeding and between degree‐days for incubation and degree‐days from hatching to mixed feeding. These last two results are chiefly because the developmental stages at hatching and at the onset of exogenous feeding are not fixed in ontogeny and are not directly related to either larval size or degree‐days for incubation, but more probably are species specific. Whatever the spawning season, which can occur almost all year long, the different trade‐offs at the early life‐stages ensure that most larvae are first feeding during spring, when food size and abundance are the most appropriate.     

Predation by a carnivorous marine copepod,Euchaeta norvegica Boeck,on eggs and larvae of the North Atlantic cod Gadus morhua L.

The predatory behavior of a carnivorous marine copepod, Euchaeta norvegica Boeck, feeding on eggs and larvae of the North Atlantic cod Gadus morhua L. was examined. In the laboratory, adult females of Euchaeta norvegica did not feed on eggs. Predation rates on yolk-sac larvae and starved post-yolk-sac larvae did not vary significantly with age up to 14 days old because of little change in size or activity of the larvae. This differs from E. elongata Esterly, a temperate congener, which selectively feeds on middle yolk-sac-stage larvae of the Pacific hake Merluccius productus Ayres. The subarctic congener Euchaeta norvegica appeared to detect tailbeats of the cod larvae. The functional response was measured for E. norvegica feeding on 2–4-day-old yolk-sac larvae. Maximum ingestion was achieved at 5 larvae · 1⁻¹ with a rate of 6.3 ± 1.2 larvae·copepod⁻¹·day⁻¹ or 10.5% of its body weight. Estimates of short-term feeding rates, determined from gut-evacuation curves, indicate that E. norvegica, when preying on cod larvae only, must feed for at least 4 h to achieve this maximum ingestion rate. Presence of copepods as alternative prey for E. norvegica depresses its predation rate on cod, although the ingestion of cod greatly supplements the ration consumed. Copepods fed cod larvae form black melanin-pigmented fecal pellets in which larval cod otoliths have been found. Approximately 0.5 larva was required to form one fecal pellet. The last three developmental stages of the predatory copepod were able to ingest larvae and form dark-pigmented fecal pellets. The feeding of this carnivorous marine copepod may contribute to the mortality noted in the larval stages of cod because E. norvegica is numerous in the center of the cod-spawning area of Skrova in the Lofoten Islands, northern Norway.     

Ontogeny of feeding in two native and one alien fish species from the Murray-Darling Basin, Australia

Investigations into the feeding of the early stages of fishes can provide insights into processes influencing recruitment. In this study, we examined ontogenetic changes in morphology and feeding behaviour of two native Australian freshwater species, Murray cod, Maccullochella peelii peelii, and golden perch, Macquaria ambigua, and the alien species, common carp, Cyprinus carpio. Murray cod free embryos are large and well developed at the onset of feeding, whereas the other two species begin exogenous feeding much younger and are smaller and less-developed. Carp commence exogenous feeding 3 days earlier than golden perch, and show more advanced development of the eyes and ingestive apparatus. We conducted feeding experiments, presenting larvae of the three species with a standardised prey mix (comprising equal numbers of small calanoid copepods, large calanoid copepods, small Daphnia, and large Daphnia). Larvae of most tested ages and species showed a preference for mid-sized prey (300–500 μm wide). This was true even when their gapes substantially exceeded the largest prey offered. Daphnia were consumed more than similar-sized copepods. The results of this study suggest that survival through their larval period will be threatened in all three species if catchable prey <500 μm in width are not available throughout such time. They also suggest that interspecific competition for prey may occur, especially when larvae are very young. The precocious development of structures involved in feeding and the extended transition from endogenous to exogenous feeding of early carp larvae are likely to have contributed to the success of this species since its introduction to Australia.     

Collection and aging of greater amberjack <Emphasis Type="Italic">Seriola dumerili</Emphasis> larvae and juveniles around the Penghu Islands,Taiwan

To investigate the early life history of Seriola dumerili, we first validated otolith daily increments using reared fish (11–51 days after hatching). Four larval and early-juvenile S. dumerili were collected in May and July 2015 around the Penghu Islands, Taiwan (23.45–23.70 °N, 119.40–119.70 °E), by surface larval net towing, but not from drifting seaweeds. Seriola dumerili were caught at the thermal front, and the total lengths and ages ranged 7.4–42.5 mm and 18–56 days, respectively. Our results indicate that the hatching dates of S. dumerili were April to June and larvae may have been accumulated in the frontal zone before the juvenile phase.     

Life history strategies of the Scotia Sea icefish, <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis>, along the Southern Scotia Ridge

Reproductive capacity can influence distribution and abundance over large spatial scales through larval dispersal, even when adult stages remain isolated following settlement. We examined size distribution, reproductive traits and age structure in Scotia Sea icefish, Chaenocephalus aceratus, an abundant benthic species with a long larval pelagic phase found on continental shelves along the Southern Scotia Ridge. In particular, we compared life history strategies between fish caught during surveys undertaken off the South Orkney Islands (SOI) and South Shetland Islands (SSI). Results corroborated regional separation after settlement and suggested distinct life history strategies, in which fish from SOI invested much less in reproduction, and somewhat more in somatic growth earlier in their life history. Compared to SSI, body weight increased faster with length and absolute fecundity was 46 % lower and increased more slowly with size for SOI population. In addition, the proportion of spawning cohorts and L _∞ was lower and k higher for SOI. The differences appeared to be a phenotypic response to environmental conditions related to regional hydrography. Lower reproductive capacity around the SOI, and strong eastward flow in the large-scale circulation, suggests that the SSI may be more important in influencing distributions and abundance of icefish along the Southern Scotia Ridge.     

The life cycle of Haemaphysalis qinghaiensis (Acari: Ixodidae) ticks under laboratory conditions

The developmental stages in the life cycle of Haemaphysalis qinghaiensis were investigated under laboratory conditions. The larval, nymphal and adult ticks were fed on sheep at 25–27 °C, 50 % relative humidity (RH) and exposed to daylight. All free-living stages were maintained in an incubator (28 °C with 90 % RH and a 12-h photoperiod). The whole life cycle of H. qinghaiensis was completed in an average of 176 days (range 118–247 days). The average developmental periods were 34.44 days for egg incubation; 5.83, 4.20 and 33.70 days for larval pre-feeding, feeding and pre-molting; and 3.88, 5.30 and 46.50 days for nymphal pre-feeding, feeding and pre-molting. The average times for pre-feeding, feeding, pre-oviposition and oviposition of female adult ticks were 2.60, 11.40, 8.50, and 19.35 days, respectively. The results confirmed the positive correlation between the weight of the engorged female and the egg mass laid (r = 0.557, P < 0.05). The reproductive efficiency index and reproductive fitness index in females were 5.49 and 4.98, respectively. Engorged nymphs moulting to females (4.53 ± 0.16 mg) were significantly heavier (P < 0.001) than those moulting to males (3.45 ± 0.19 mg). The overall sex ratio of the adult ticks was 1:1.1 (M:F).     

Early life history timings in marbled rockcod (Notothenia rossii) fingerlings from the South Shetland Islands as revealed by otolith microincrement

Although it has been reported that Notothenia rossii elsewhere hatches in spring, our daily increment back-counting from the capture date in otoliths of fingerlings caught in Potter Cove, South Shetland Islands, in the 2000s, showed two main periods of larval hatching, one in summer (February–March) and another in winter (July). In concordance, the simultaneous presence of two cohorts born the same year was identified in the age/length frequency distribution of fish sampled in spring 2010, which belonged to biological ages 0+ and 1+ and hatched, respectively, in summer and winter–spring. Maximum and minimum ages of pelagic blue-phase and demersal brown-phase fingerlings were, respectively, 227 and 240 days, indicating a demersal settlement after about 8 months from hatching. The estimated growth rate was 0.23–0.33 mm/day, equivalent to that of South Georgia fingerlings and higher than those of other nototheniids of similar size range. Based on early life events associated with the hatching periods, two types of life cycles are hypothesised for South Shetland fingerlings. The pelagic blue-phase fingerlings (6.5–7.6 cm TL, age group 0+) hatched in July (winter cohort), entering in Potter Cove in February–March. The brown-phase fingerlings (6.3–10.6 cm, mostly of age group 0+) hatched in February–March (summer cohort) and were collected in the cove in spring (the smaller specimens) or in summer (the larger ones). Finally, early juveniles (10.7–15.5 cm, age group 1+) hatched in winter, mainly in July (winter cohort), entering in the cove the following year to spend the second winter inshore.     

Effects of temperature on the development and circannual control of pupation in the carpenter moth, <Emphasis Type="Italic">Cossus insularis</Emphasis> (Lepidoptera: Cossidae), reared on an artificial diet

The effects of temperature on larval development and the timing of pupation in the carpenter moth, Cossus insularis (Staudinger) (Lepidoptera: Cossidae) were examined by artificial rearing under different temperatures and the same photoperiod (15L:9D). Although C. insularis pupated and emerged at 20, 25, and 30 °C, the pupation rate was lower at 20 °C than at 25 and 30 °C. These results suggest that the optimum temperature range for preadult development is 25–30 °C. The duration of larval development was about 260 days for the first pupation group at 25 and 30 °C, and at least 600 days at 20 °C. Therefore, the C. insularis generation time was 2 years or more, as the total effective temperature for development from hatching to the pupal stage was unlikely to be reached within 1 year in Tokushima Prefecture. The second group pupated at 25 °C, about 200 days after the first group. This periodicity of pupation was likely due to the free-running period of the circannual rhythm. Furthermore, although only the first group pupated at 30 °C, the peak was almost synchronous with the first group at 25 °C. These results indicate that the timing of the first pupation group in C. insularis is temperature compensated. Therefore we propose that the presence of an endogenous rhythm during the development of C. insularis is evidence for a circannual rhythm related to the timing of pupation.     

Fatty acid composition of lipid-rich myctophids and mackerel icefish (<Emphasis Type="Italic">Champsocephalus gunnari</Emphasis>) – Southern Ocean food-web implications

The lipid content, fatty acid composition and calorific value of seven species of mesopelagic deep-sea fish of the family Myctophidae and the mackerel icefish, Champsocephalus gunnari, important in the diet of Southern Ocean marine predators, are presented. Fish were sampled at the Kerguelen Plateau (KP) and Macquarie Ridge (MR) in the Indian and Pacific sectors of the Southern Ocean respectively, to examine geographic variation in lipid compositon. All species of myctophid from KP and Electrona antarctica from MR were high in lipid content (6-18% wet mass), particularly Gymnoscopelus nicholsi (18%) and E. antarctica (15%). The mackerel icefish, and G. fraseri and Protomyctophum tenisoni from MR were generally lower in lipid content (3-5%) and varied significantly in fatty acid composition from KP species. KP myctophids were high in calorific content (9.3 kJ g^-1 wet mass) when compared with icefish (5.4 kJ g^-1 wet mass) and other published values for prey items of marine predators such as squid (1.7-4.5 kJ g^-1). KP myctophids were distinguished from each other and from C. gunnari and MR specimens by cluster and discriminant function analysis using six fatty acids (16:0, 18:1̩, 20:1̩, 22:1Ὃ, 20:5̣, 22:6̣). Findings presented here highlight trophic links between high-latitude fish and their prey and emphasise the importance of myctophids as a significant energy source for marine predators foraging in the Polar Frontal Zone.     

The complete mitochondrial genome of the mackerel icefish,Champsocephalus gunnari (Actinopterygii: Channichthyidae), with reference to the evolution of mitochondrial genomes in Antarctic notothenioids

The mackerel icefish (Champsocephalus gunnari Lönnberg, 1905) is a ray‐finned fish living in the Southern Ocean around Antarctica. We sequenced the complete mitochondrial (mt) genome of the mackerel icefish and a segment from cytochrome b to the control region (CR) in 32 individuals. The mt genome of the mackerel icefish was rearranged, containing two nicotinamide adenine dinucleotide (reduced form) dehydrogenase subunit 6 (ND6), two tRNA^Glu, and two CRs. However, variations in numbers of ND6 and tRNA^Glu were observed amongst individuals. These variations included type 1 (containing two ND6 and two tRNA^Glu), type 2 (containing one ND6, one incomplete ND6, and one tRNA^Glu), and type 3 (containing one ND6 and one tRNA^Glu). The gene orders of types 1 and 2, and variations in numbers of ND6 and tRNA^Glu were not previously found in any Antarctic notothenioids, whereas type 3 is the same as that of Racovitzia glacialis. Phylogenetic analyses of CR DNA sequences showed that duplicated CRs of the same species formed a monophyletic group, suggesting that duplication of CRs occurred in each species. The frequent duplication of mt genomes in Antarctic notothenioids is an unusual feature in vertebrates. We propose that interspecific hybridization and impairment of mismatch repair might account for the high frequency of gene duplications and rearrangement of mt genomes in Antarctic notothenioids.     

Ontogenetic development of the digestive tract in Cuban gar (Atractosteus tristoechus) larvae

Histological method was used to describe the development of the digestive tract in Atractosteus tristoechus larvae reared under culture conditions. The larvae were kept at 28 ± 1 °C in three 15 L circular tanks for 18 days and they were fed with Artemia. According to the structural changes in the digestive system, three significant stages were established: (1) lecithotrophic, (2) lecithoexotrophic and (3) exotrophic. The first stage spanned from hatching to 3 days after hatching (DAH), the digestive system started to differentiate and larvae depended entirely on the endogenous nutrition from the yolk sac. During second stage (4–10 DAH), considered critical since it is the transition period to exotrophic feeding, the digestive tract was fully differentiated into buccopharynx, esophagus, non-glandular and glandular stomach, anterior and posterior intestine. First periodic Schiff reagent-positive goblet cells also appeared, interdispersed within the epithelium of the digestive tract, increasing substantially in numbers and distribution as development continued. At this early stage, gastric glands were only observed in the fundic stomach and not in the cardiac and pyloric region. Pyloric caeca, spiral valve and rectum were also clearly distinguishable in the intestine. After the onset of the exogenous feeding (11–18 DAH), the organization and differentiation of the digestive tract did not undergo any noticeable modification, only the increase in size and complexity of the structures, and it attained the four tissue layer arrangement characteristic of adult vertebrates.