The present study deals with the effect of exogenous treatment of O. niloticus females with L-thyroxine (T 4) on the development of the digestive system during larval rearing, and its subsequent effect on larval growth and survival. The development of the digestive tract and accessory glands was investigated histologically and histochemically in the developing O. niloticus larvae, from control and T 4-treated spawners. During yolk-sac absorption, the digestive system of the fish underwent further differentiation and the rudimentary alimentary canal became segmented into four different histological regions: the buccopharynx, oesophagus, stomach and intestine. The injection of females O. niloticus with thyroxine (1 or 10 μg•T 4 /g•BW) greatly enhanced the development of the digestive tract and accessory glands of larvae as indicated by the quantitative and qualitative changes of the mucus composition from predominantly neutral to a mixture of neutral and acid mucosubstances, or acid mucosubstances occurred during the rearing period for the larvae produced from T 4-treated females. This may be due to the direct effect of exogenous thyroxine, which might have been transferred from maternal circulation into the oocytes and larvae, on the synthesis of proteins, which increased with larval development. Thus, thyroxine directly or indirectly improved O. niloticus larval growth, since a marked increase in both, length and weight of larvae occurred during the experimental period. In addition, larvae from treated females also gave a significantly higher survival rate than that of control. It could be concluded that exogenous T 4 in maternal circulation might have been transferred into oocytes and larvae. The transferred thyroid hormone appears to play some role in the early development of larvae and may confer a distinct advantage for the growth of the offspring of the Nile tilapia, O. niloticus.

The present study deals with the morphological adaptations of digestive tract according to food and feeding habits of the broomtail wrasse, Cheilinus lunulatus. The highest rate of feeding activity was recorded during spring and the lowest during summer. In the older and younger fish, the rates of feeding activity are nearly similar. The fish is mainly carnivorous benthic feeder. This fish plays an important role as a predator of invertebrates of reef fauna. It consumes a wide range of animal food. Molluscs, echinoderms and small fishes were the main food items consumed by these fish. Molluscs increased and echinoderms decreased in the food with the increasing length of the fish. The mouth is relatively large, terminal in position, usually with prominent lips. Jaws are extremely protrusible to make the fish able to get food between branches of coral reef. The jaws teeth are conical canine in shape and composed of outer uni-serial pointed teeth. Two enlarged teeth are present in the front of the upper and lower jaws. They are specialized for catching and holding the prey and preventing its escape out of the buccal cavity. The pharyngeal teeth are molar in shape with blunt or round edge and arranged in two rows, usually 7-17 in each row of the floor. The teeth in the roof are developed and haphazard distributed. These molariform teeth are adapted for crushing and grinding of hard body preys. 11 gill rakers are present on the bowshaped gill arch and conical in shape with tapering tips adapted for binding the prey. Oesophagus is a short muscular distensible tube with few number of large mucosal folds adapted for facilitating conduction of food to the stomach. The Jshaped stomach is of the siphon type with large number of small mucosal folds adapted for food retention to be digested. The intestine is a short uncomplicated tube which recognized by the presence of ileo-rectal valve modified to prevent the passage of food particles into the posterior part before intestinal digestion and absorption is completed. It contains very large number of mucosal folds adapted for facilitating lubrication of feces towards the anus.

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