Growth and ontogenetic development of digestive functionality in black Amur bream (Megalobrama terminalis)

The function of digestive physiology during ontogenetic development is essential to ensure high survival and growth rates. In order to evaluate the digestive physiological capacity of the black Amur bream (Megalobrama terminalis), changes of morphology and digestive enzyme activity (trypsin, lipase, amylase, pepsin, leucine aminopeptidase and alkaline phosphatase) in larvae were examined from hatching to 40 days after hatching (DAH). Results indicated that fluctuation patterns differed between the total and specific activities of the digestive enzymes. The total activities of these six enzymes gradually increased throughout the fish growth. The specific activity of trypsin peaked at 5 DAH and then decreased dramatically, while it increased remarkably again from 8 to 10 DAH and remained stable level after 20 DAH. Pepsin activity was first examined in M. terminalis at 15 DAH and gradually elevated towards the end of the experiment. The specific activity of lipase displayed obvious peaks at 5 and 20 DAH. For the amylase, its specific activity reached plateau at 4 DAH, underwent sharp decrease, and remained stable after 20 DAH. In addition, we found that the specific activity of alkaline phosphatase raised significantly from hatching to 5 DAH, and tended to keep slight fluctuation after 15 DAH. From the above, we concluded that the specific activities of digestive enzymes in the larvae varied constantly from 3 to 20 DAH and turned relatively stable after 20 DAH. The present study provides effective information that is useful to improve the seedling cultivation and the technology for healthy breeding.     

Influence of light intensity on feeding, growth, and early survival of leopard coral grouper (Plectropomus leopardus) larvae under mass-scale rearing conditions

This study investigated the effect of different light intensities on feeding, growth and survival of early stage leopard coral grouper Plectropomus leopardus larvae. Four different light intensities (0, 500, 1000 and 3000 lx) were used and larvae were kept under constant light conditions from 0 day after hatching (DAH) to 5 DAH. The larvae were fed a small S-type of Thai strain rotifers at a density of 20 individuals/mL from 2 DAH. The number of rotifers in larval digestive organ and total length of larvae were examined at 3 h intervals between 04:00 and 22:00 h on 3 DAH, and thereafter at 6 h intervals until the end of the experiment (5 DAH). Four experimental trials of the larval rearing were repeated using by 60 kL mass-scale rearing tanks. The results indicate that coral grouper larvae are visual feeders and their food intake increases with increasing light intensity. Food intake of larvae reared at 3000 lx was significantly higher than those reared at 0–1000 lx on 3 DAH despite being the first-feeding day (P < 0.01). On 4 DAH, total length of larvae reared at 3000 lx was significantly larger than those reared at the lower light intensities (0, 500 and 1000 lx), and thereafter light intensity significantly influenced larval feeding and growth until the end of the experiment. Survival on 5 DAH did not show a significant difference between light intensities, but survival rate at 3000 lx and 1000 lx had a tendency to be higher than those reared at the lower light intensities (0 and 500 lx). In contrast, larvae reared at 0 lx exhibited stagnant and/or negative growth. These results indicate that light intensity is significantly the factor affecting larval feeding, growth, and survival in coral grouper larvae under the rearing conditions.     

Ontogenic development of digestive enzymes in bigfin reef squid (Sepioteuthis lessoniana)

Bigfin reef squid (Sepioteuthis lessoniana) is an economically important exported aquatic animal in Thailand, but little is known about its husbandry, which needs to be clarified. In this study, the ontogenic development of the main digestive enzymes (pepsin, trypsin, chymotrypsin, lipase and amylase) was investigated within 30 days after hatching (DAH). Fertilized eggs of the wild cuttlefish were hatched and then distributed into four replicate aquaria assigned to varying collection times (0, 5, 10, 15, 20, 25 and 30 DAH). The development of pepsin suggests acidic digestion functionality at 5 DAH, and its specific activity was maintained over the studied period. Specific activities of the serine proteases, trypsin and chymotrypsin, fluctuated significantly with similar pattern, and appear to be the key enzymes contributing ontogenic changes in protein catabolism. The specific activity of lipase was relatively high at 0 DAH, dramatically increased by 5 DAH, and then appeared constant until the end of observations, suggesting important role in utilizing the lipid from yolk at hatching, as well as probably in sparing protein utilization. Dramatic increase in amylase specific activity occurred by 10 DAH after which the activity was constant until 30 DAH, suggesting the utilization of carbohydrate as energy evolves comparatively late. Findings from the current study could be used to manage nutritional protocols according to the digestive enzyme patterns, as well as to develop artificial diets for rearing S. lessoniana.     

Early weaning of cuttlefish (Sepia officinalis,L.) with frozen grass shrimp (Palaemonetes varians) from the first day after hatching

The suitability of early weaning cuttlefish using frozen grass shrimp, and its effects on growth and mortality was determined in a 50‐day experiment. Three food groups were used. One group (C) was fed with live prey until 25th DAH and weaned with frozen prey until the end of the experiment. In the other two groups, weaning started at the fifth DAH (W5) and first DAH (W1), also with frozen diet. Significant differences were found between C and the remaining treatments (P < 0.05) for mean wet weight (MWW), instantaneous growth rate (IGR), biomass (B) and mortality at the 25th and the 50th DAH. Despite the lower growth (~1/3 of the achieved with live food) and higher mortality (3% obtained by C versus 23% in the W1 and W5 groups), C cuttlefish presented a similar weight gain tendency to W1 and W5 groups after weaning. This is the first record of early acceptance (at the first DAH) of frozen food by cuttlefish hatchlings. These differences could be related with digestive enzymes of cuttlefish and prey, changes in nutritional composition and amount of captured prey, etc. Future research should also address the effects of this early weaning on cuttlefish life cycle.     

Effects of the timing of initial feeding on growth and survival of loach (<Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>) larvae

The effects of delayed first feeding on growth and survival and starvation on the point-of-no-return of loach Misgurnus anguillicaudatus larvae were studied by evaluating morphometric characteristics under controlled conditions. Larvae began to feed exogenously at 3 days after hatching (DAH) and the PNR occurred between 9 and 10 DAH at 23 ± 1.0°C. The experimental design included a conventional feeding regime with initial feeding from 3 DAH as a control, delayed first feeding for 4, 5 and 6 DAH. Morphometric characteristics (head depth, body depth, eye diameter, mouth diameter, musculature height, total length and yolk sac volume) were evaluated under different initial feeding time (3, 4, 5 and 6 days after hatching). Loach larvae initiated first feeding at 4, 5 and 6 days after hatching achieved comparatively lesser growth performance in all morphometric characteristics than that of 3 days at the end of the experiment. By day 6, significant differences were observed between 3 and 6 days initial feeding larvae for all morphometric characteristics except eye diameter and mouth diameter. Similarly, significant differences were noticed between 3 and 5 days initial feeding. However, there were no significant differences in head depth, body depth, eye diameter, mouth diameter, and total length between 3 and 4 days initial feeding until 12 DAH. After 15 days rearing, significant differences in all morphometric characteristics appeared between 3 and 4 days initial feeding and followed to the end of the experiment. It was also observed that the yolk absorption in loach larvae was completed by 6 days irrespective of the differences in the initial feeding. The yolk volume of 4 and 5 DAH larvae initiated first feeding at 3 days (0.0125 ± 0.0015; 0.0077 ± 0.0009 mm³) had significant differences compared with yolk volume of larvae initiated first feeding at 4 days (0.0081 ± 0.0011; 0.0039 ± 0.0004 mm³), 5 days (0.0079 ± 0.0010; 0.0017 ± 0.0002 mm³) and 6 days (0.0082 ± 0.0011; 0.0016 ± 0.0001 mm³). Survival rates of four treatments were estimated daily for 30 days and significant differences were observed between the treatments at the end of the experiment. The final survival rate was higher when the loach larvae initiated feeding at 3 days (75.9%) when compared with 4 days (31.8%), 5 days (14.5%) and 6 days (6.4%). The present study suggests that the first feeding of loach larvae should be initiated at 3 DAH for achieving better growth and survival or else bad growth performance will engender if the first feeding is delayed.     

Skeletal development and abnormalities of the vertebral column and fins in larval stage of hatchery‐reared American shad,Alosa sapidissima

The present study describes the skeletal development and the occurrence of deformities in American shad, Alosa sapidissima, larvae from hatching to 45 days after hatching (DAH). The ontogeny of the vertebral column started at 16 DAH (days after hatching), with the formation of the posterior neural and haemal arches, and was complete at 28 DAH. In comparison, the vertebral centra started to form at 16 DAH, with ossification being visible in all centra at 38 DAH. The pectorals were the only fins that formed before the onset of feeding (at 2 DAH), with ossification being complete at 45 DAH. The caudal fin formed at 5 DAH, with ossification being complete at 40 DAH. Dorsal and pelvic fin development began at 6 DAH and 20 DAH respectively. The ossification of both the dorsal and pelvic fins was visible at 45 DAH. The anal fin began forming at 14 DAH, and was complete at 30 DAH. The ossification of the anal fin was complete at 45 DAH. Overall, 22 types of skeletal deformities were detected in about 41% of individuals. Most anomalies were detected in the haemal region, while the fewest anomalies were detected in the anal fin. In addition, the frequency of deformities gradually increased with fish age at the different developmental stages. Our results are expected to contribute baseline information on how rearing conditions impact skeletal development, in addition to identifying potential causative factors of skeletal deformities.     

野生和养殖曼氏无针乌贼亲体形态、生化组分及其胚胎发育的比较

为优化曼氏无针乌贼人工繁育技术,提高人工增殖苗种的产量与质量,采用实验生态学方法,对比分析了野生和养殖曼氏无针乌贼（Sepiella japonica）的表观形态、生化组分及其受精卵的形态差异,探究了光照周期与受精卵胶质外膜对曼氏无针乌贼胚胎发育的影响。结果显示：野生和养殖曼氏无针乌贼的表观形态、生化组分均存在显著差异,野生群体性成熟规格远大于养殖群体,肌肉和肝脏组织中的脂肪含量显著低于养殖群体（P<0.05）,卵巢中的蛋白质含量则显著高于养殖群体（P<0.05）;养殖亲体所产黑卵在12D12L光照周期条件下孵化率最高,所产白卵在24D和24L条件下孵化率最高,野生亲体所产卵在24D和12D12L条件下孵化率最高;随光照时间的延长,受精卵的平均孵化时间具有先增加后减小的趋势,表明光照周期是影响曼氏无针乌贼胚胎发育的重要因素;实验发现,将受精卵胶质外膜剥离处理后,养殖亲体所产黑白卵的平均孵化时间具有减少的趋势,但孵化率显著下降（P<0.05）。综上所述,建议在曼氏无针乌贼人工苗种生产过程中,尽量选用大规格野生乌贼作为繁育亲体。此外,在受精卵孵化期间,应对孵化池进行适当遮光处理,避免受精卵长时间暴露于强光照环境中,以提高孵化率和仔乌成活率。本实验研究结果可为曼氏无针乌贼人工苗种繁育技术优化提供参考。     

Embryonic and larval development of serpae tetra Hyphessobrycon eques (Steindachner, 1882)

In this study, the embryonic and larval development stages of one of the most important ornamental fish serpae tetra (Hyphessobrycon eques) are described. The early life stage is documented from fertilization until the beginning of the juvenile period. The fertilized eggs (the average diameter = 938.55 ± 35.20 µm) were incubated at a water temperature of 26 ± 0.5°C. The cleavage finished in 1:10 hr (=h) and the early blastula stage occurred at 1:26 hr post fertilization (hpf). The gastrulation started at 3:05 hpf, and 50% epiboly was observed at 3:25 hpf. Segmentation stage was monitored at 7:26 hpf. Embryonic developmental stage was completed and hatching occurred 20–21 hpf. The total length (TL) of newly hatched larvae was 2.64 ± 0.21 mm. The larval development of serpae tetra was divided into four different periods: Yolk‐sac larva (1–4 DAH, TL = 2.77 ± 0.09 mm ‐ 3.85 ± 0.11 mm), preflexion larva (5–12 DAH), flexion larva (13–15 DAH, TL = 5.78 ± 0.46 mm on the 15th day) and post‐flexion larva (16–30 DAH, TL = 10.7 ± 0.27 mm on the 28th–30th days). The mouth and anus are closed at 1 DAH. The mouth and anus opened at 4 DAH. Exogenous feeding started on the 4th day. The first gulping of the swim bladder was on days 3. The larva begins to swim freely, and the yolk sac was completely consumed at 4 DAH. Histological structures of the eye and brain of new hatched larva were clearly identified at 1 day after hatching (DAH). According to histological findings, the digestive system (stomach, intestine) started to develop and the liver could be seen on the ventral side of the swim bladder at 5 DAH. No histological difference was observed between the anterior intestine and the posterior intestine at 15–16 DAH. The larval metamorphosis was completed, and the larvae transformed into juveniles at 28–30 DAH.     

Screening of enzyme activity for assessing the condition of larvae in the seven-band grouper <Emphasis Type="Italic">Epinephelus septemfasciatus</Emphasis> and devil stinger <Emphasis Type="Italic">Inimicus japonicus</Emphasis>

We conducted screening tests to determine whether enzyme activity is a suitable biomarker for assessing the physiological condition of marine fish larvae. The rearing experiments consisted of three trials, of which two were conducted using the seven-band grouper Epinephelus septemfasciatus for a period of 5 days after hatching (DAH), and one was conducted using the devil stinger Inimicus japonicus for 10 DAH. The trials were conducted under three different rearing-tank environments (shallow tank, intermediate tank, deep tank) in a water volume of 100 l and an aeration rate of 50 ml/min. We determined survival, surface death, growth, and enzyme activities (trypsin, esterase, and alkaline phosphatase). The highest survival rates and lowest surface deaths in both species occurred among the larvae grown in the deep tank. There was a significant and negative correlation between survival at 5 DAH and alkaline phosphatase activity at 0 DAH in the seven-band grouper. The same correlation was found between survival at 10 DAH and trypsin and alkaline phosphatase activity at 1 DAH in the devil stinger. Based on these results, we conclude that the activity of a specific enzyme is a candidate for assessing the physiological condition of marine fish larvae.     

虎斑乌贼喷墨卵与正常卵的比较

为了探明虎斑乌贼喷墨卵对孵化及胚胎发育的影响,采用单因子实验研究了喷墨卵与正常卵的孵化率、培育周期、孵化周期、初孵幼体体质量,并比较了剥膜喷墨卵、剥膜正常卵、喷墨卵、正常卵4种类型卵的幼体生长和存活率。结果显示,虎斑乌贼喷墨卵和正常卵的孵化率无显著差异,喷墨卵的孵化率为90.1%±1.5%,正常卵的孵化率为87.9%±0.7%;两种卵的初孵幼体体质量也无显著差异,喷墨卵的初孵幼体体质量为(0.18±0.01)g,正常卵的初孵幼体体质量为(0.17±0.01)g;两种卵的培育周期、孵化周期均无显著差异,喷墨卵的培育周期为(34.67±0.89)d,孵化周期为(14.33±0.44)d,而正常卵的培育周期为(35.33±0.44)d,孵化周期为(14.67±0.67)d。而剥膜喷墨卵、剥膜正常卵、喷墨卵、正常卵4种类型卵的幼体存活率差异显著,剥膜喷墨卵和剥膜正常卵的存活率明显小于喷墨卵和正常卵,而剥膜喷墨卵和剥膜正常卵之间、喷墨卵和正常卵之间的存活率无显著差异;4种类型的幼体日均增长量和增重量差异显著,剥膜喷墨卵和剥膜正常卵的幼体日均增长量和增重量明显小于喷墨卵和正常卵,而剥膜喷墨卵和剥膜正常卵之间、喷墨卵和正常卵之间的幼体日均增长量和增重量无显著差异。     

Effect of zooplankton as diet for the early paralarvae of Patagonian red octopus,Enteroctopus megalocyathus,grown under controlled environment

The limited success reported in the paralarval culture of merobenthic octopus is mainly attributed to nutritional problems. This study aimed to determine the effect of live diets on the paralarvae performance during the first 30 days after hatching (DAH). The paralarvae were grown under different treatments: starved (STV) as negative control or fed four diets: Artemia sp. enriched with microalgae (ANCH), Artemia enriched with a commercial enrichment (AOG), Artemia enriched with microalga + commercial enrichment (AMIX) and king crab zoea (ZKC). The paralarval growth and survival were affected by the dietary treatment, with significant higher growth in ANCH and AMIX. STV showed 100% mortality at day 27, whereas all diets resulted within a range from 20% to 33% survival. The endogenous protein and lipid reserves were utilized in all treatments. The 22:6n‐3/20:5n‐3 ratio increased up to 16% during the experimental period. Alkaline protease activity tended to increase in paralarvae fed ANCH, AOG and ZKC over the first 13 DAH; however, this effect was not observed in trypsin nor chymotrypsin activities. The leucine aminopeptidase activity (LAP) was not affected by the dietary treatment, while alkaline phosphatases increased only at 13 DAH in paralarvae fed ANCH. Indicators of the nutritional status of paralarvae are discussed.     

Histological development of digestive tract in discus, <Emphasis Type="Italic">Symphysodon</Emphasis> spp. larvae

The present study provides information on the histomorphological development of digestive system of discus, Symphyosodon spp., larvae during the first month of life. Discus larvae are altricial at hatching, with an undifferentiated digestive tract and a large yolksac, which is completely consumed within 7 days. The mouth opens 3 days after hatching (DAH) and the larvae starts feeding on AF Artemia at 4 DAH when offered. At 3 DAH the digestive tract is differentiated with distinct esophagus, stomach anlage, and mid- and hindguts. At 5 DAH, discus larvae is an active feeder, equipped with partly developed jaws and ossified gill arches and an inflated swim bladder. The liver and pancreas are present and supranuclear inclusion vacuoles (SIV) appear in the hindgut for the first time. Gastric glands in stomach were first observed 7 DAH and proliferated by 11–13 DAH. SIV were a common feature in the midgut and hindgut epithelium until 15–23 DAH. Therefore, exclusive use of artificial diets should be postponed until 2–3 weeks after hatching.     

An intensive hatchery rearing protocol for larvae of the bullseye puffer,Sphoeroides annulatus (Jenyns)

In this study bullseye puffer, Sphoeroides annulatus larvae were reared from hatching through to 1 or 2 months after weaning on an experimental scale in three replicate 600 L tanks and on three occasions during the spawning season (nine tanks in total). The rearing protocol used was green water (Nannochloropsis oculata and Isochrysis sp.) 100 000 cells mL^?1 from 0 to 11 days after hatch (DAH), 5–10 rotifers, Brachionus rotundiformis mL^?1 from 2 to 26 DAH, 0.1–1 Artemia mL^?1 from 21 to 34 DAH and weaning from 29 to 34 DAH. Survival to a month after weaning was 1%, a total of 3153 juveniles were produced with an average wet weight of 0.29 ± 0.07 g and a length of 27.5 ± 0.82 mm.     

The effect of light intensity on performance of larval pike-perch (Sander lucioperca)

In this work performance parameters of larval pike-perch (Sander lucioperca) reared under four different light intensities (100, 500, 1000 and 2500 lx) until 21 days post hatch (dph) were investigated. As performance parameters change in length and weight, swim bladder inflation, feed consumption, natural mortality, stress induced mortality and RNA-DNA ratio were measured. Aim was to investigate the influence of light intensity on pike-perch performance during the first three weeks of larval rearing. Significant differences were found in natural and stress induced mortality as well as in weight growth. No single light exposure level combined optimal performance of all tested performance parameters. Highest light intensity of 2500 lx showed good weight growth but an increase in stress induced mortality. Bright light of 500 and 1000 lx intensity was found to improve growth and stress mortality whereas dim light conditions of 100 lx showed significantly lower natural mortality. Thus data suggested that most favorable illumination during larval pike-perch rearing comprise a tradeoff between optimal natural mortality under dim light conditions (100 lx) or optimal larval growth and stress resistance under bright light conditions (500 and 1000 lx). It is shown that high light intensities during larval rearing can be beneficial for pike-perch rearing if offspring supply is not limited.     

Organogenesis of exocrine pancreas in sharpsnout sea bream (<Emphasis Type="Italic">Diplodus puntazzo</Emphasis>) larvae: characterization of trypsin expression

The ontogeny and differentiation stages of digestive systems related with trypsin expression in larvae of sharpsnout sea bream, Diplodus puntazzo, were investigated from hatching to 40 DAH (days after hatching), and total lengths and weights of larvae were determined. Histologic and enzymatic techniques were used to explain the functional development of the pancreas including trypsin activity. The pancreas was identified as a compact structure located in the region slightly posterior to the liver. At 3 DAH, first anus and then mouth opened. Incipient pancreas secretion polyhedral cells could be first observed as zymogen granules. During larval metamorphosis, the pancreas became diffuse, spreading throughout the mesentery in proximity to the stomach, the anterior intestine and the pyloric caeca. The specific activity of trypsin (42.54 ± 6.8 mU/mg protein⁻¹) was found as early as after hatching at larvae size of 2.87 ± 0.34 mm at 0 DAH. Activity further increased until 10 DAH, especially after exogenous feeding. The highest trypsin activity was detected at 25 DAH as 119.26 ± 11.6 mU/mg protein⁻¹. It is concluded that exocrine pancreas organogenesis is the main critical step in the development of digestive system that results in zymogen granules accumulation and increased trypsin activity.     

Reduction of skeletal anomalies in meagre (Argyrosomus regius,Asso, 1801) through early introduction of inert diet

The consolidation of meagre (Argyrosomus regius) in aquaculture requires an understanding and optimization of larval rearing and nutritional conditions. The aim of this study was to analyse the effects of an early introduction of inert diets during larval rearing, on growth performance, digestive enzymes activity and development of skeletal anomalies. This study evaluated the effects of three different timings for the introduction of inert diet during larval rearing: a control group (CTRL) where inert diet was initiated at 14 days after hatching (DAH) and two treatment groups that had an earlier introduction of inert diet at 8 DAH (T1) and 11 DAH (T2). Meagre larvae exhibited similar pancreatic and intestinal enzymatic activities among the different dietary treatments. No differences in the overall prevalence of anomalies were observed between treatments at 25 or 50 DAH, however, a significant reduction was observed in all groups with the transition from larval to juvenile stage. The precocious introduction of inert diet shifted the distribution of vertebral anomalies to a more anterior vertebral column region. Altogether, this study shows that earlier introduction of inert diets in meagre hatcheries can be beneficial for meagre production in aquaculture.     

Correlation between gut microbial diversity and flatulence of silver pomfret (Pampus argenteus) during ontogenesis

Gut microorganisms play an important role in host health and have susceptibility to diseases, undergoing a distinct transformation at early stages of development. This study aimed to determine the regulation of gut microorganism development from fertilized eggs to 150 DAH (days after hatching) and the differences between flatulent and healthy silver pomfret (Pampus argenteus). High‐throughput sequencing was used to analyze the diversity and relative abundance of microorganisms. PICRUSt was used to predict functional alterations of dominant microorganisms. The results showed that from all 42 samples, a total of 3,746,895 reads were obtained, representing 6,081 operational taxonomic units (OTUs). Top 3 phyla were Proteobacteria, Firmicutes and Bacteroidetes. From 0 to 32 DAH, the relative abundance of Proteobacteria continuously increased and peaked at 94.99%. After that, the abundance of Proteobacteria decreased, but Bacteroidetes and Firmicutes increased instead. Alpha diversity is the lowest at 32 DAH, the difference is significant compared with others, p < .05. Comparing flatulent fish with healthy fish, the former has more specific OTUs, higher diversity and abundance. There were four genera Ethanoligenens, Methanobacterium, Caproiciproducens and Leptolinea that only obtained from the flatulent samples, but almost none in the healthy samples. All of these four genera are directly or indirectly involved in gas metabolism. This study enriched the basic research of silver pomfret, for the first time, focused on flatulent individuals which would provide a theoretical basis for the subsequent breeding.     

Faster growth before metamorphosis leads to a higher risk of pseudoalbinism in juveniles of the starry flounder <Emphasis Type="Italic">Platichthys stellatus</Emphasis>, as suggested by otolith back-calculation

The mechanism underlying malformation during flatfish metamorphosis is not clear. Here, the relationship between growth before metamorphosis and the occurrence of malformation after metamorphosis was examined in individuals reared in a single tank. Otoliths of starry flounder Platichthys stellatus larvae were labeled with alizarin complexone before metamorphosis [12 days after hatching (DAH)]. The positive linear regression between the lapillus otolith diameter and body length at 12 DAH enabled the estimation of individual larval size after completion of metamorphosis. At 12 DAH, the average body length of the typical pseudoalbino juveniles was significantly greater (5.37 mm) than that of the normal juveniles (5.13 mm) (P < 0.01, n = 100). In addition, of the larvae that were estimated to measure less than 4.8 mm at 12 DAH, approximately 80% metamorphosed into normal juveniles, whereas more than 60% of the larvae that measured more than 5.4 mm became pseudoalbino juveniles. These results indicate that the larvae that grow rapidly during the first 12 days are more likely to become pseudoalbino individuals after metamorphosis.     

The effect of timing of extended photoperiod on growth and maturity of brook trout (Salvelinus fontinalis)

The influence of timing of extended photoperiods on growth and maturity of brook trout was investigated in a 112‐day experiment. The fish with mean initial weight of ~192 g were reared under four light regimes: one control group with natural ambient photoperiod and three groups exposed to an 18L:6D regime initiated at days 1, 23 or 46 of the growth trial. Light‐emitting diodes, with intensity of 250–1000 lux, depending on the distance from the light source, were used for extending light periods. There was a positive effect of prolonged day length on fish growth (p < 0.05), and a delay in gonad development and sexual maturity. Significantly higher numbers of sexually mature fish were found among controls groups, regardless of sex. Survival rate was not affected by light regime. This study demonstrated that the short‐term expansion of the photo period delayed maturation and increased the growth rate of brook trout.     

Partial sequence characterization and ontogenetic expression of genes involved in lipid metabolism in the tropical gar (Atractosteus tropicus)

The tropical gar (Atractosteus tropicus) is an economically and socially important freshwater fish species from southeastern Mexico, with high aquaculture potential. This study determined the expression of acetyl‐CoA carboxylase (ACC1), fatty acid synthase (FAS), and carnitine palmitoyl transferase 1 (CPT1C) in several tissues of adult specimens, as well as in early ontogeny stages of tropical gar. Partial sequences of all genes were obtained for brain, liver, muscle, mesenteric adipose, kidney, testis, gill, and heart in males. Specific qPCR primers were used to compare the expression between tissues and also during larviculture, starting with embryos (0 days after hatching, [DAH]), and at 5, 10, 15, 20, 25, and 30 DAH. Mesenteric adipose tissue, liver, and muscle showed maximum FAS, ACC1, and CPT1C expression. Additionally, the highest expression of lipogenic genes was detected in embryos (0 DAH), decreasing between 5 and 10 DAH, then increasing at 15 DAH, and ultimately decreasing again from 20 DAH onwards. Based on these results, it can be concluded that genes encoding ACC1, FAS, and CPT1C are expressed differentially across tissues of tropical gar adults, and are regulated during larval development.