**Introduction:**
Chicken and fish are both sources of protein and can be used interchangeably in many recipes. Therefore, they are considered substitutes in the eyes of consumers. When the price of one substitute increases, it is expected that the demand for the other substitute will be affected.

**Price Increase of Chicken:**
If the price of chicken increases, it means that consumers have to pay more to purchase chicken. This higher price may lead consumers to look for alternative options, such as fish, which may be relatively cheaper compared to chicken. As a result, the demand for fish is expected to be affected.

**Effect on Demand for Fish:**
There are several possible scenarios regarding the effect on the demand for fish when the price of chicken increases:

1. **Increase in Demand for Fish:** If the increase in chicken price is significant and consumers find fish to be a more affordable alternative, the demand for fish may increase. This could be due to the substitution effect, where consumers switch from a relatively expensive good (chicken) to a relatively cheaper good (fish).

2. **No Change in Demand for Fish but Movement Along the Demand Curve:** If the increase in chicken price is not substantial or if consumers do not consider fish as a suitable substitute, the demand for fish may not change. However, there could be a movement along the demand curve for fish, as consumers may choose to consume less chicken and more fish due to the price difference.

3. **Decrease in Demand for Fish:** In some cases, consumers may still prefer chicken over fish despite the price increase. This could be due to factors such as taste preferences or habit. As a result, the demand for fish may decrease, as consumers are less likely to switch to fish as a substitute.

**Shift in Demand Curve for Fish:**
The demand curve for fish represents the relationship between the price of fish and the quantity of fish demanded. The shift in the demand curve for fish can be influenced by factors other than the price of chicken, such as changes in consumer income, tastes and preferences, or the availability of other substitutes.

1. **Rightward Shift:** If there is an increase in consumer income, a positive change in tastes and preferences towards fish, or a decrease in the price of other substitutes for fish, the demand for fish could increase. This would result in a rightward shift of the demand curve for fish.

2. **Leftward Shift:** Conversely, if there is a decrease in consumer income, a negative change in tastes and preferences towards fish, or an increase in the price of other substitutes for fish, the demand for fish could decrease. This would result in a leftward shift of the demand curve for fish.

**Conclusion:**
In conclusion, when the price of chicken increases, the demand for fish can be influenced in various ways. It may increase, remain unchanged with a movement along the demand curve, or decrease. The shift in the demand curve for fish can also occur due to factors other than the price of chicken. Therefore, it is important to consider these factors when analyzing the relationship between the price of substitutes and their respective demands.