Morphology and muscle gene expression in GIFT and Supreme Nile tilapia varieties reared in two cultivation systems.

Tissue growth in most fishes occurs by muscular hyperplasia and hypertrophy, which are influenced by different regulatory factors, such as myostatin. The current study evaluated the influence of cultivation in hapas and earthen ponds on the diameter of white muscle fibers and on the myostatin (MSTN-1) gene in GIFT and Supreme varieties of tilapia. Fish of both varieties were reared for 204 days and then divided into four developmental stages. White muscle samples, corresponding to 100 fibers per slide, were collected from the middle region of fish of each variety and cultivation system, and were measured and divided into two classes representing hyperplasia and hypertrophy. Samples were subjected to real-time PCR to analyze gene expression. Hyperplasia decreased during the developing stages, coupled with increased hypertrophy. There was a higher rate of hypertrophy in fish raised in earthen ponds when compared to those raised in hapas, during juvenile and developing phases, and greater hypertrophic growth was observed in GIFT specimens when compared to Supreme specimens in earthen ponds. Since increased MSTN-1 gene expression was observed in GIFT specimens during the developing phase in pond cultivations, and in Supreme tilapia in hapas, MSTN-1 expression is related to greater hypertrophy. These results demonstrate the capacity for increased muscle growth in earthen pond cultivation in which the GIFT variety developed best. How the environment affects the growth of different tilapia varieties may be employed to optimize culture management and genetic improvement programs. Further investigations should aim to describe mechanisms affecting muscle growth and development.

Growth of Nile tilapia Oreochromis niloticus fed with different levels of alcohol yeast.

Two hundred and forty 45-day-old fingerlings of Nile tilapia (Oreochromis niloticus), sexually reverted with an initial average weight of 1.25 +/- 0.14 g, distributed in a totally casualized delineation, during 330 days. The effect of the substitution of 10%, 20% and 30% of the ration by distillery yeast (Saccharomiyces cerevisae) in balanced experimental rations on the development in the breeding of tilapias did not show a harmful effect up to the maximum tested level of 30%, showing that the choice of the yeast in the ration for these fishes depends on the availability and occasional cost. The yeast provides fish with good resistance to unfavorable environmental conditions, which could be verified since there were no statistical differences among the treatments with different levels of yeast and the witness. The long growth rate in terms of length and weight can be attributed to the little available space for each specimen, not obeying the limit of populational density, as well as reduction of food ingestion, which coincide with the winter season, above of the absence of natural feeding.

Effect of cocaine on xylazine analgesic activity.

The effect of cocaine on the antinociceptive action of xylazine (XLZ) was studied by the method of abdominal contortions in mice. While XLZ alone (0.5 mg/kg, sc) inhibited the contortions by 43%, cocaine (5 mg/kg, sc) produced 39% inhibition and combination of the two drugs reduced the contortions by 77%. Cocaine acted synergistically with XLZ, decreasing the ED50 from 0.42 to 0.13 mg/kg. The mechanism involved does not seem to be directly mediated by activation of alpha-2 receptors since pretreatment of the animals with yohimbine did not significantly influence the XLZ effect.

Further studies on the xylazine-yohimbine interaction.

A study of the Yohimbine-blocking action upon Xylazine-ability to inhibit the abdominal contortions elicited by an intraperitoneal injection of Acetic Acid (60 mg/kg) was carried out. Xylazine (0.75 mg/kg - subcutaneously) inhibited 44% of the abdominal contortions. Such an inhibition activity was reduced to a 19% level after a previous Yohimbine treatment (1 mg/kg - intramuscularly - 30 min before). The results suggested there is a 2.9 times reduction of Xylazine affinity for CNS alpha 2 receptors, and that the antagonism between the two drugs is of a competitive nature.