Nigiri is sushi made of rice with a topping (fish, egg etc) on top. This is the first image Japanese people have of sushi, as opposed to the rolled sushi with seaweed around it (which is called maki zushi). Sushi shops sell both types, but nigiri sushi is slightly more popular than maki zushi.
長次郎 (ちょう・じ・ろう） is just the name, and it is made up of;
長 (long)、次 (next), 郎 (son)
次郎 by itself is a very common traditional name, meaning second son. First son is 一郎 （いち・ろう） (Ichiro) Third son is 三郎 （さぶ・ろう）(Saburo)
Now lets look at the white writing on red.
There are three words on three lines, the first line at the top says;
Reading; かつ・ぎょ (katsugyo) Meaning; live fish
活 lively, living, かつ、い（きる）、い（かす）、い（ける）（Katsu, ikiru, ikasu, ikeru)
grade: 2 frequency: 171 JLPT level: 3 活動 action, activity かつ・どう (katsudo) 生活 living せい・かつ (seikatsu)
魚 fish ギョ、うお…