No abstract

The content (% wet mass) in water, ash, lipid, crude protein, DNA and RNA of different tissues was determined during sexual maturation of bonitos Sarda sarda from the Aegean Sea. A total of 220 specimens were collected in the following stages of sexual maturity: immature, resting, developing, mature, spawning and spent. Highest lipid levels in the white muscle, red muscle and liver were measured in immature specimens, while lowest levels were found in spawning bonitos. The gradual percentage of lipid reduction from immature to spawning bonitos was relatively higher in the liver (females 71Á2% and males 64Á4%) than in the white (females 59Á2% and males 53Á5%) and red (females 62Á1% and males 51Á7%) muscle. Lipid levels in the gonads increased gradually from the immature to spawning stage. The decrease of lipid in the somatic tissues was more intense in females than in males, and gonadal lipid content was higher in females than in males. There was a strong reverse correlation between water and lipid percentage in all tissues. Protein content decreased significantly only in spawning bonitos. The percentage of protein reduction from immature to spawning stage was relatively higher in males than in females in both white (females 3Á4% and males 4Á6%) and red (females 4Á6% and males 5Á1%) muscles. Protein content in the liver was significantly lower than in the other tissues, being highest in mature females. Gonadal protein content in females increased with maturation and decreased after spawning. The content in ash exhibited considerable stability. The RNA:DNA ratio exhibited a similar pattern of variation in both muscles. The RNA:DNA ratio increased during gonadal development gradually from the developing to spent stage. It was concluded that in S. sarda during gonadal development, there was an increase in gonadal lipid accompanied by a decrease in somatic tissue lipid reserves. Thus, reproductive inactive bonitos have more lipid in their edible part and a higher nutritional value than active ones.

No abstract

Growth is a polygenic and environmentally controlled trait with the most influential genes being those of growth hormone (GH) and insulin‐like growth factor‐I (IGF‐I), as they consist the core of the hypothalamic–pituitary–somatotropic (HPS) axis. As a result, the influence of environmental and dietary conditions on GH and IGF‐I gene expression has a great potential in planning to optimize fish health and production, as growth rate of fish is a key factor in aquaculture. In this review, we provide a molecular and physiological overview of GH and IGF‐I gene expression as well as all the participating factors regulating GH/IGF‐I axis in growth. We further discuss the genetic, dietary and environmental factors affecting growth rate. More importantly, how external factors in combination with diet such as temperature, photoperiod, salinity, pollutants and stocking density affect GH and IGF‐I expression and growth rate. In addition, there is evidence that photoperiod effect varies among species by altering the seasonal cycle of GH and IGF‐I gene expression and biological cycle of fish. Pollution has also a variable effect on GH, IGF‐I and fish growth rate, depending on the pollutant, species and sex. Finally, increased stocking density influences the HPS axis and growth, dependent on species, temperature and the stage of growth. Notably, interactions among these factors were observed by the reported importance, primarily feeding‐related stress one of the most important factors, while environmental would add or subtract on each other’s optimal or suboptimal conditions in a hierarchy of significance, as further discussed.