In a certain code language CHICKEN is written as DHJCLEO. How will FISHN be written in that code language?

Let us inspect the correspondence between the letters of $\text{CHICKEN}$ and its code $\text{DHJCLEO}$:
* $\text{C}\stackrel{+1}{\to }\text{D}$
* $\text{H}\stackrel{+0}{\to }\text{H}$
* $\text{I}\stackrel{+1}{\to }\text{J}$
* $\text{C}\stackrel{+0}{\to }\text{C}$
* $\text{K}\stackrel{+1}{\to }\text{L}$
* $\text{E}\stackrel{+0}{\to }\text{E}$
* $\text{N}\stackrel{+1}{\to }\text{O}$

The pattern shows alternating shifts of $+1$ and $+0$. Applying this to the word $\text{FISHN}$:

* $\text{F}\stackrel{+1}{\to }\text{G}$
* $\text{I}\stackrel{+0}{\to }\text{I}$
* $\text{S}\stackrel{+1}{\to }\text{T}$
* $\text{H}\stackrel{+0}{\to }\text{H}$
* $\text{N}\stackrel{+1}{\to }\text{O}$

The resulting code is $\text{GITHO}$.