Ontogeny of digestive enzymes in clown anemonefish larvae, Amphiprion ocellaris (Perciformes: Pomacentridae)

Introduction: Clown anemonefish (Amphiprion ocellaris) is the most popular fish species in the marine aquarium trade, however, there is a lack of information on their digestive physiology during larvae ontogeny, valuable information that helps in the design of specific diets, as well as management protocols for the species. Objective: Characterize the early development of digestive enzymes of A. ocellaris during larvae ontogeny. Methods: From hatching until the 38th day after hatching (DAH), the specific activity of acid and alkaline proteases, trypsin, chymotrypsin, leucine aminopeptidase and lipase were analyzed, while acid and alkaline proteases zymograms were performed. Results: At hatching, all measured enzymes activities were detected. Acid proteases increased in activity from hatching until the 38th DAH. Alkaline proteases, trypsin, chymotrypsin, and leucine aminopeptidase showed the same pattern and maximum activity on the 8th DAH, decreasing at the 38th DAH. Lipase activity showed peaks on the 8th and 30th DAH. Acid zymogram showed a single band, appearing on the 8th DAH. A total of eight alkaline proteases were revealed (154.2, 128.1, 104.0, 59.8, 53.5, 41.9, 36.5 and 25.1 KDa), showing seven bands on the 1st DAH and all bands from the 3rd to 8th DAH, decreasing at two bands (41.9 and 25.1 KDa) in the 38th DAH. Conclusion: A. ocellaris shows a functional stomach on the 8th DAH, where the species on the 38th DAH shows digestive enzymatic pattern to omnivore with a tendency to carnivory. Objective: Characterize the early development of digesive enzymes of A. ocellaris during larval ontogeny. Methods: From hatching until the 38th days after hatching (DAH), the specific activity of acid and alkaline proteases, trypsin, chymotrypsin, leucine aminopeptidase and lipase were analysed, while acid and alkaline proteases zymograms were perfomed. Results: At hatching, all measured enzymes activities were detected. Acid proteases increased in activity from hatching until the 38th DAH. Alkaline proteases, trypsin, chymotrypsin and leucine aminopeptidase showed same pattern and maximum activity on the 8th DAH, decreasing at the 38th DAH. Lipase showed activity peaks on the 8th and 30th DAH. Acid zymogram showed a single band, appearing on the 8th DAH. Total of eight alkaline proteases were reveled (154.2, 128.1, 104.0, 59.8, 53.5, 41.9, 36.5 and 25.1 KDa), showing seven bands on the 1st DAH and all band from the 3rd to 8th DAH, decreasing at two bands (41.9 and 25.1 KDa) in the 38th DAH. Conclusion: Therefore, A. ocellaris shows functional stomach on the 8th DAH, where the species on the 38th DAH shows digestive enzymatic pattern to omnivore with a tendency to carnivory.

Effect of salinity on growth, survival, and serum osmolality of red snapper, Lutjanus campechanus

Three trials were conducted to evaluate the performances of red snapper, Lutjanus campechanus, in low salinities. The median lethal concentration (96 h LC50) of salinity was determined by trimmed Spearman-Karber method using survival data of fish (18.9 ± 0.2 g) collected after 96 h from acclimation to 2, 4, 8, and 32 ppt salinities in 800 L tanks (n = 3), while the serum osmolality of fish (74.1 ± 3.9 g) was determined after 48 h from acclimation to 6, 8, 16, 24, and 32 ppt salinities in 150 L tanks (n = 3). The growth trial was conducted for 6 weeks in 800 L tanks to determine the growth and survival of fish (18.8 ± 0.2 g) at 8 ppt salinity compared to the control (32 ppt salinity). At the conclusion, the isosmotic point of fish was estimated as 357.2 mmol/kg (correspond to 11.0 ppt salinity), while the 96 h LC50 was estimated as 5.65 ppt salinity. No significant differences were noted for survival and FCR of fish reared in 8 and 32 ppt salinities. However, growth was significantly lower in fish reared in 8 ppt salinity compared to the fish reared in 32 ppt salinity. The reduced growth could be, at least partially, due to the increased osmoregulatory energy expenditure at lower salinities.

Revision of the diagnostic characters of two morphologically similar snook species, Centropomus viridis and C. nigrescens (Carangiformes: Centropomidae)

Historically, the taxonomic identification of the two snook species, Centropomus viridis and C. nigrescens, has been challenging due to their morphological similarity and the inconsistency of the characters used for diagnosis. Therefore, this study aimed to evaluate the usefulness of the morphologic, meristic, and morphometric characters currently being used to identify C. viridis and C. nigrescens, based on molecular data. The results showed that the gas-bladder shape (i.e., C. viridis with diverticula and C. nigrescens without diverticula) was the only morphological character univocally related to genetic identification. Likewise, geometric morphometrics separated two groups; each corresponds to only one of two genetically (and gas bladder shape) identified species. Of all the meristic characters examined, only the second dorsal fin ray count (nine for C. viridis and ten for C. nigrescens) was related to the gas bladder shape and genetic identity; therefore, it is the only external character with a diagnostic utility to separate each species.

The Efficacy of Geraniol and ß-Citronellol against Freshwater and Marine Monogeneans

Monogeneans are parasitic flatworms that may be a threat for finfish aquaculture. In this study, the anthelmintic activity of two terpenes, geraniol and β-citronellol, was tested in vitro against ancyrocephalin and diplectanid monogeneans. Experiments were performed in both water and a culture medium. We observed that monogeneans in culture medium may be more tolerant to treatments compared with bioassays performed only in water. Concentrations of 300 mg/L of both compounds were required to kill 100% of monogeneans at 1 h postexposure. The toxicity of β-citronellol to fish was not evaluated. However, geraniol at 300 mg/L and 150 mg/L killed juvenile Nile Tilapia Oreochromis niloticus and White Snook Centropomus viridis, respectively, after a few minutes. Therefore, the present work suggests that other alternatives should be studied for use against monogeneans in aquaculture.

Characterization and proliferation capacity of potentially pathogenic fungi in marine and freshwater fish commercial feeds

In the aquaculture industry, the selection and quality of feed are highly relevant because their integrity and management have an impact on the health and development of organisms. In general, feeds contamination depends on storage conditions and formulation. Furthermore, it has been recognized that filamentous fungi are among the most important contaminating agent in formulated feeds. Therefore, the purpose of this research was to identify saprophytic fungi capable of proliferating in commercial feeds, as well as determining their prevalence, extracellular enzymes profile, ability to assimilate carbon sources, and finally their ability to produce aflatoxins. In order to do that, twenty-two fungi were isolated from commercial fish feeds. After, the species Aspergillus chevalieri, A. cristatus, A. sydowii, A. versicolor, A. flavus, A. creber, and Lichtheimia ramosa were identified. These fungi were able to produce extracellular enzymes, such as phosphatases, esterases, proteases, β-glucosidase, and N-acetyl-β-glucosaminidase. The isolated fungi showed no selective behavior in the assimilation of the different carbon sources, showing a strong metabolic diversity. Prevalence percentages above 85% were recorded. Among all fungi studied, A. flavus M3-C1 had the highest production of aflatoxins when this strain was inoculated directly in the feeds (295 ppb). The aflatoxin production by this strain under the experimental setting is above the permitted levels, and it has been established that high levels of aflatoxins in feeds can cause alterations in fish growth as well as the development of cancerous tumors in the liver, in addition to enhancing mortality.

Susceptibility of Pacific white snook Centropomus viridis to Vibrio species

To examine the pathogenicity of Vibrio strains, several doses of Vibrio harveyi (CAIM 1622 and CAIM 1508), Vibrio ponticus (CAIM 1751) and Vibrio anguillarum (CAIM 8) were used to challenge Pacific white snook Centropomus viridis Lockington, 1877 juveniles, and survival, gross signs and histological lesions were observed. Susceptibility of pathogenic vibrios CAIM 1508 and CAIM 1751 to antibiotics used in aquaculture was also evaluated. The growth ability of the tested strains was not related to their pathogenicity. One of the V. harveyi strains (CAIM 1508) was the most virulent, causing per-acute septicaemia in C. viridis even at a low dose (1.4 × 104 CFU g-1). Although the V. ponticus strain (CAIM 1751) was less virulent, this is the first report of it as a pathogen of white snook. Fish challenged with V. ponticus displayed external, generalized haemorrhaging. Necrosis of the digestive tract and intravascular haemosiderosis were the most remarkable histological lesions in fish challenged with both strains. Multifocal necrosis of the internal organs and bacterial masses was also observed. The lowest minimum inhibitory concentration of the pathogenic strains (CAIM 1508 and CAIM 1751) was calculated for enrofloxacin (20 and 10 µg ml-1, respectively), and both bacteria were resistant to amoxicillin, ampicillin and trimethoprim-sulfamethoxazole.

Embryonic development of the bullseye puffer Sphoeroides annulatus (Tetraodontidae): A morphofunctional approach to ontogenetic steps

The embryonic development of the bullseye puffer, Sphoeroides annulatus, was characterized on the basis of the theory of saltatory ontogeny. This theory predicts a correlative relationship between the ontogeny-type in an altricial-precocial spectrum and the habitat that a species occupies within an unstable-stable environmental spectrum. Because S. annulatus inhabits a variety of unstable environments along a wide latitudinal range, the hypothesis that this species presents one of the most altricial embryonic developments among tetraodontids was tested. Based on major developmental events that marked the ontogenetic thresholds nine embryonic steps were identified. Developmental features such as small adhesives eggs, lack of vitelline circulation, small free embryos swimming up at hatching guided by positive phototaxis, and small first-feeding larvae actively swam in the water column, suggest that S. annulatus belongs to the reproductive guild of the nonguarders-lithopelagophils. Moreover, a comparative analysis of the developmental sequences, egg size, and first-feeding larvae size between tetraodontids confirms the hypothesis of this study and supports the evolutionary principle of the altricial-precocial spectrum postulated in the theory of saltatory ontogeny.

Immunostimulation and trained immunity in marine fish larvae

Little is known about the strategies for immunization and immunostimulation in marine fish larvae; however, both strategies have the potential to improve survival during the first days of larval culture. The biological variety of marine fish larvae complicates the standardization of the application of these strategies, although the mechanisms of early development are similar in marine species of commercial importance and those with aquaculture potential. Immunostimulation experiments performed with fish larvae provide evidence that helps to further understand the mechanisms of trained immunity, which can be used to understand responses to immunostimulation treatments. Therefore, during the stages of marine fish larviculture, strategic planning is required for the standardization of immunostimulation methods. A standardized method could improve our understanding of the effects of immunostimulating agents on the maturation of immune systems in marine fish larvae; this information would enhance the ability to achieve early training of innate immunity and determine its potential to improve the survival of cultured larvae.

Histological study of the gastrointestinal tract in longfin yellowtail (Seriola rivoliana) larvae

This work contributes basic knowledge on larval development of Seriola rivoliana. A histological study describes the development of the digestive tract and accessory glands in S. rivoliana larvae reared under laboratory conditions at 24 °C from hatching to 30 days post-hatching (DPH). At hatching (2.6 ± 0.12 mm), larvae had an undifferentiated digestive tract with a closed straight tube and a large yolk sac with an oil globule. The liver and pancreas were observed at 1 and 2 days, and the mouth and anus opened at day 2. Enriched rotifers were visible in their digestive tract. At the beginning of the pre-flexion stage, a mixed nutritional period was observed. At day 3, exogenous feeding began; the digestive tract became differentiated into the buccopharynx, esophagus, an undifferentiated stomach, and the intestines. Zymogen granules were visible in the exocrine pancreas. At day 4, supranuclear vacuoles were present in the posterior intestine, indicating the beginning of intracellular digestion. At day 5, goblet cells were present in the esophagus and became functional at day 7 in the esophagus and intestine. The buccopharynx goblet cells developed at day 15. The presence of gastric glands and differentiation of the stomach in the fundic, cardiac, and pyloric regions during the post-flexion stage occurred at day 20. This was the onset of the juvenile period and the beginning of weaning; however, a long co-feeding phase is recommended. Pyloric caeca were observed at day 30 (13.6 ± 1.6 mm). These results provide valuable information on S. rivoliana larvae biology and digestive physiology, which should be useful to improve cultivation techniques and identify ecological features involved in ontogeny.

Expression of myostatin in the spotted rose snapper Lutjanus guttatus during larval and juvenile development under cultured conditions

In this study, the developmental expression pattern of myostatin (mstn) in the spotted rose snapper Lutjanus guttatus under culture conditions is presented. The full coding sequence of mstn from L. guttatus was isolated from muscle tissue, obtaining 1134 nucleotides which encode a peptide of 377 amino acids. The phylogenetic analysis indicated that this sequence corresponds to mstn-1. mstn expression was detected in embryonic stages, and maintained at low levels until 28 days post-hatch, when it showed a significant increase, coinciding with the onset of metamorphosis. After that, expression was fluctuating, coinciding probably with periods of rapid and slow muscle growth or individual growth rates. mstn expression was also analysed by body mass with higher levels detected in smaller animals, irrespective of age. mstn was also expressed in other tissues from L. guttatus, presenting higher levels in brain, eye and gill. In brain for instance, two variants of mstn were isolated, both coding sequences were identical to muscle, except that one of them contained a 75 nucleotide deletion in exon 1, maintaining the reading frame but deleting two conserved cysteine residues. Phylogenetic analysis indicated that this brain variant was also mstn-1. The function of this variant is not clear and needs further investigation. These results indicate that mstn-1 participates in different physiological processes other than muscle growth in fishes.

[Osteological development of the vertebral column and caudal complex of Lujanus guttatus (Perciformes: Lutjanidae) larvae under rearing conditions]

The spotted rose snapper (Lutjanus guttatus) is an important commercial species in Mexico with good culture potential. The osteological study at early stages in this species is an important tool to confirm normal bone structure and for the detection of malformations that may occur during early development. This study was carried out in order to evaluate and describe the normal osteological development of the vertebral column and caudal complex of this species grown under controlled conditions. For this, a total of 540 larvae of L. guttatus, between 2.1 and 17.5 mm of total length (TL), were cultured during 36 days; culture conditions were 28 degrees C, 5.74 mg/L oxygen and 32.2 ups salinity with standard feeding rates. To detect growth changes, a sample of 15 organisms was daily taken from day one until day 36 of post-hatch (DPH). Samples were processed following standard techniques of clearing, and cartilage (alcian blue) and bone staining (alizarin red). Results showed that the vertebral column is composed of ten vertebrae in the abdominal region, and 14 vertebrae including the urostyle in the caudal region. The development of the axial skeleton starts with the neural arches and haemal arches at 3.8 mm TL. Caudal elements such as the hypurals and parahypural began to develop at 4.1 mm TL. Pre-flexion and flexion of the notochord and the formation of all hypurals were observed between 5.3 and 5.8 mm TL. Ossification of the vertebrae in the abdominal region and in some neural arches initiated at 9.5mm TL. In the caudal region, all the neural and haemal arches ossified at 10.2 mm TL. All the abdominal vertebrae and their respective neural arches and parapophyses ossified at 11.2 mm TL, while the elements of the caudal complex that ossified were the hypurals, parahypurals and modified haemal spines. All caudal fm rays, 12 neural spines and 3 haemal arches were ossified by 15.5 mm. The complete ossification process of this specie under laboratory culture conditions was observed when larvae reached 17.3 mm TL on 36 DPH. Detailed analysis of the osteological structures will allow a reference description to evaluate and detect malformations that may occur during the larval culture of the spotted rose snapper.

[The mitotic and meiotic chromosomes of the tropical fish Petenia splendida (Cichlidae)]

The karyotype of bay snook, Petenia splendida, is described based on mitotic and meiotic stages of sixty larvae and twelve juveniles from Tabasco, Mexico. Standard cytological procedures with minor modifications were followed to obtain mitotic and meiotic chromosome spreads. One hundred chromosome slides were analyzed and 290 chromosome spreads were counted. High-quality spreads in mitosis and meiosis were used for karyotype analysis. Mitotic chromosome spreads showed 76.7% of such cells with 2n=48 chromosomes, while meiotic spreads revealed 55.2% with 24 chromosomes in haploid stage. Photographic documentation of eight high-quality pictures showed that the karyotype consists of three pairs of bi-armed metacentric-submetacentric chromosomes (msm) and 21 pairs with uni-armed subtelocentric-acrocentric chromosomes (sta), with a fundamental number (FN) of 54 arms. Karyotype chromosomes were verified by analysis of haploid and diploid metaphases at meiotic stage I. Abundant chromosome spreads were observed more frequently on slides from larvae. No evidence ofheteromorphism to discriminate sexual chromosomes was detected. There were "dot-like" chromatic bodies in both sexes and they were classified as "B" chromosomes. The karyotype of P. splendida is type "A", i.e., primitive in the Cichlid family, similar to other species of Cichlasoma. The occurrence of supernumerary chromosomes is still unknown: studies on the effects of pollution and hybridization might be important to understand that phenomenon.