Physiology, leptin gene expression, and intestinal morphology of pinhead and starved milkfish (Chanos chanos).

"Pinhead" is an abnormal condition of farmed fish which is rarely studied, albeit well known among fish culturists, and is characterized by extreme emaciation and anorexia. In this study, the potential impacts of pinhead condition in milkfish were analyzed and compared to fed, healthy, and a group starved for four weeks. The condition factor and hepatosomatic index of pinhead milkfish were significantly lower compared with fed, healthy individuals. Abnormal plasma osmolality and muscle water content in pinhead milkfish indicated an imbalance in their internal water content. The anorexigenic hormone, leptin A was highly expressed in liver of pinhead milkfish, which could be related to their lack of appetite. Meanwhile, the hepatosomatic index, intestinal somatic index, enterocyte height, number of villi and goblet cells, Na⁺/K⁺- ATPase activity, and intestinal protein content of the pinhead milkfish were similar to those of the 4-week starved individuals. Taken together, our results characterized key physiological parameters of pinhead milkfish for the first time. Further investigation is required to understand how environmental or artificial stress can lead to the occurrence of pinhead milkfish, and to develop methods for alleviating this condition.