fastaq_merge: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/fastaq_merge - from package: fastaq

You may install the required package with command apt-get install {package}

Error in other languages:
fastaq_merge: bevel nie gevind nie
fastaq_merge: comandă negăsită
fastaq_merge: comando não encontrado
fastaq_merge: commande introuvable
fastaq_merge: command not found
fastaq_merge: käsku ei ole
fastaq_merge: không tìm thấy lệnh
fastaq_merge: komanda nerasta
fastaq_merge: Kommando nicht gefunden.
fastaq_merge: kommandot finns inte
fastaq_merge: komut yok
fastaq_merge: nie znaleziono polecenia
fastaq_merge: níor aimsíodh an t-ordú
fastaq_merge: no se encontró la orden
fastaq_merge: no s'ha trobat l'ordre
fastaq_merge: opdracht niet gevonden
fastaq_merge: parancs nem található
fastaq_merge: perintah tidak ditemukan
fastaq_merge: príkaz nenájdený
fastaq_merge: příkaz nenalezen
fastaq_merge: команда не найдена
fastaq_merge: командата не е открита
fastaq_merge: 命令找不到
fastaq_merge: コマンドが見つかりません