Abstrak
The estuarine waters of Bulungan have great potential for the capture fisheries sector. Mackerel (Scomberomorus sp) is one of the fish caught in the estuarine waters in Bulungan using fishing gear. The eating habits of mackerel fish depend on food availability in the estuarine waters of Bulungan. Food is influenced by the quality and quantity of what is eaten, so food determines the fish's growth and condition. A lack of food will limit the number of fish populations in the waters. This research aimed to determine fish's eating habits in the estuarine waters of Bulungan. The samples were collected from catches from October to November 2022; carried out in three times. Thirty fish samples were taken to represent the population of the number caught. The entire catch was taken if the catch was less than 30 fish. Observation of eating habits was carried out by measuring the total length of the fish's body weight, taking the fish's stomach, and weighing the weight of fish's stomach and the innards of fish's stomach. Water quality measurements are carried out in situ and ex-situ. The aspects analyzed were gastric fullness (PILB) and gastric fullness index (ISC). The results of this research consisted of fish (Chordata) with a PILB value percentage of 44.83-92.86%, indicating that the estuarine waters Bulungan are fluctuating waters with sufficient food availability. The ISC value of 0.2-1.76% can be caused by the fish's habit of searching for food and obtaining food availability. The food found in the stomach of mackerel fish falls into the carnivore category. The ease with which fish find food is influenced by the behaviour of the fish and its food characteristics.