Predicted 2100 climate scenarios affects growth and skeletal development of tambaqui (Colossoma macropomum) larvae.

Climate changes driven by greenhouse gas emissions have been occurring in an accelerated degree, affecting environmental dynamics and living beings. Among all affected biomes, the Amazon is particularly subjected to adverse impacts, such as temperature rises and water acidification. This study aimed to evaluate the impacts of predicted climate change on initial growth and development of an important Amazonian food fish, the tambaqui. We analyzed growth performance, and monitored the initial osteogenic process and the emergence of skeletal anomalies, when larvae were exposed to three climate change scenarios: mild (B1, increase of 1.8°C, 200 ppm of CO2); moderate (A1B, 2.8°C, 400 ppm of CO2); and drastic (A2, 3.4°C, 850 ppm of CO2), in addition to a control room that simulated the current climatic conditions of a pristine tropical forest. The exposure to climate change scenarios (B1, A1B, and A2) resulted in low survival, especially for the animals exposed to A2, (24.7 ± 1.0%). Zootechnical performance under the B1 and A1B scenarios was higher when compared to current and A2, except for condition factor, which was higher in current (2.64 ± 0.09) and A1B (2.41 ± 0.14) scenarios. However, skeletal analysis revealed higher incidences of abnormalities in larvae exposed to A1B (34.82%) and A2 (39.91%) scenarios when compared to current (15.38%). Furthermore, the bone-staining process revealed that after 16 days posthatch (7.8 ± 0.01 mm total length), skeletal structures were still cartilaginous, showing no mineralization in all scenarios. We concluded that tambaqui larvae are well-adapted to high temperatures and may survive mild climate change. However, facing more severe climate conditions, its initial development may be compromised, resulting in high mortality rates and increased incidence of skeletal anomalies, giving evidence that global climate change will hamper tambaqui larvae growth and skeletal ontogeny.

Effect of prey concentrations and feed training on production of Hoplias lacerdae juvenile.

The aim of this work was to investigate the effects of daily prey concentration during the first 15 days of active feeding of Hoplias lacerdae larvae, and the juvenile size on the feed training. In the first phase, the larvae received five Artemia nauplii concentrations (P). In the second phase, the juveniles from each treatment were trained to accept formulated diet. Superior growth was related to higher initial daily prey concentrations (900 and 1100 nauplii larvae-1). During feed training, the growth tendency was similar to that verified in the first phase. The lowest values of specific growth rate (SGR) were registered after the introduction of the semi-moist diet used in the feed training. However, the values of SGR recovered along the experiment and similar rates were found among the treatments. Survival, mortality and cannibalism were similar in the different treatments at the end of both phases. It can be concluded that: the prey concentration affects growth of H. lacerdae during the first 15 days of active feeding, and feed training can be initialized with juveniles of about 16 mm of total length.

Short periods of fasting followed by refeeding change the expression of muscle growth-related genes in juvenile Nile tilapia (Oreochromis niloticus).

Muscle growth mechanisms are controlled by molecular pathways that can be affected by fasting and refeeding. In this study, we hypothesized that short period of fasting followed by refeeding would change the expression of muscle growth-related genes in juvenile Nile tilapia (Oreochromis niloticus). The aim of this study was to analyze the expression of MyoD, myogenin and myostatin and the muscle growth characteristics in the white muscle of juvenile Nile tilapia during short period of fasting followed by refeeding. Juvenile fish were divided into three groups: (FC) control, feeding continuously for 42 days, (F5) 5 days of fasting and 37 days of refeeding, and (F10) 10 days of fasting and 32 days of refeeding. At days 5 (D5), 10 (D10), 20 (D20) and 42 (D42), fish (n=14 per group) were anesthetized and euthanized for morphological, morphometric and gene expression analyses. During the refeeding, fasted fish gained weight continuously and, at the end of the experiment (D42), F5 showed total compensatory mass gain. After 5 and 10 days of fasting, a significant increase in the muscle fiber frequency (class 20) occurred in F5 and F10 compared to FC that showed a high muscle fiber frequency in class 40. At D42, the muscle fiber frequency in class 20 was higher in F5. After 5 days of fasting, MyoD and myogenin gene expressions were lower and myostatin expression levels were higher in F5 and F10 compared to FC; at D42, MyoD, myogenin and myostatin gene expression was similar among all groups. In conclusion, this study showed that short periods of fasting promoted muscle fiber atrophy in the juvenile Nile tilapia and the refeeding caused compensatory mass gain and changed the expression of muscle growth-related genes that promote muscle growth. These fasting and refeeding protocols have proven useful for understanding the effects of alternative warm fish feeding strategies on muscle growth-related genes.

Quantitative expression of myogenic regulatory factors MyoD and myogenin in pacu (Piaractus mesopotamicus) skeletal muscle during growth.

Skeletal muscle growth is regulated by differential expression of myogenic regulatory factors (MRFs). We evaluated hyperplasia, hypertrophy and quantitative expression of MRFs MyoD and myogenin in 45, 90, 180, and 400 days post-hatching (dph) and adult pacu (Piaractus mesopotamicus) skeletal muscle. Transverse sections of white dorsal muscles were obtained to evaluate hypertrophy and hyperplasia. MyoD and myogenin gene expression was determined by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR). Pacu skeletal muscle had similar morphology at all stages. The highest and the lowest frequencies of fiber diameters <20 µm were found at the 45 dph and adult stages, respectively. Their frequency was similar in the 90, 180, and 400 dph stages. The highest percentage of >50 µm diameter fibers were found in 180 and 400 dph, and adult fish. Hyperplasia was the main mechanism observed in pacu skeletal muscle growth at 45dph; this declined through 90, 180, and 400 dph and remained low in adult fish; the latter presented hypertrophy as the main mechanism responsible for skeletal muscle growth. The high frequencies of 20-50 µm diameter fibers at 90, 180, and 400 dph can be related to intense hypertrophy. The mRNA levels for MyoD and myogenin were similar in 45, 90, and 400 dph and adult fish, peaking at 180 dph. The high MyoD expression at 180 dph can be related to intense myoblast proliferation and hyperplasia, while high myogenin expression can be related to intense myoblast differentiation and fusion during hypertrophy. MyoD and myogenin expression patterns in adults can respectively be associated with myoblast proliferation and differentiation, which both contribute to hypertrophy. Differential MyoD and myogenin expression in pacu white muscle probably is associated with differences in growth patterns during the stages analyzed. In this study, the 180 dph pacu could represent an interesting phase to investigate suitable strategies in commercial fish production focusing on skeletal muscle growth improvement to raise healthy, fast-growing fish.

Tolerance to the air exposition test of Hoplias lacerdae larvae and juvenile during its initial development

O estabelecimento de parâmetros para avaliação da qualidade de larvas e juvenis produzidos intensivamente é altamente desejável. Nesse sentido, o experimento teve o objetivo de avaliar a Taxa de Resistência ao Estresse (Re) em larvas e juvenis de trairão. Larvas foram submetidas a testes para a avaliação da Re no 13°, 16°, 19°, 23° e 26° dia de vida. Vinte animais foram separados em béqueres de um litro e mantidos em temperatura entre 27 e 28,5°C. Em seguida realizaram-se os seguintes tratamentos: E3. 3 minutos; E5. 5 minutos; E7. 7 minutos; E10. 10 minutos e E15. 15 minutos sobre o papel secante. Após 24 horas foi verificada a Re. Observou-se que a Re apresentou um aumento nos valores do 13° ao 19° dia em todos os tratamentos. Foram observadas elevadas Re durante todo o trabalho, sendo os menores valores (P<0,05) encontrados para E10 (67,7% no 13° dia) e para E15 (41,25% no 26° dia). Concluiu-se que larvas e juvenis de trairão são resistentes à exposição ao ar sobre papel secante e que exposição superior a sete minutos é mais adequada para avaliação da Re de larvas e juvenis de trairão submetidos a diferentes condições de cultivo.

The zymogen-enteropeptidase system: A practical approach to study the regulation of enzyme activity by proteolytic cleavage*.

The present research describes an efficient procedure to obtain high levels of trypsinogen and chymotrypsinogen by using a simple, rapid, and easily reproducible method. The extraction process and the time-course of activation of zymogens can be carried out in a single laboratory period, without sophisticated equipment. The main objective was to prepare a laboratory class that would stimulate student interest in enzyme regulation, exploring the fact that the catalytic activity of some enzymes is regulated by different mechanisms. The regulation of proteolytic enzymes requires the synthesis of an inactive zymogen and its being irreversibly "switched on" by specific proteolytic cleavage.