An L-number is not a formal scientific designation, but it allows people to identify various loricariid catfish by a "common name" before the fish is officially described.
ɐn ˈɛlnˈʌmbɚɹ ɪz nˌɑːɾə fˈɔːɹməl saɪəntˈɪfɪk dˌɛzɪɡnˈeɪʃən, bˌʌt ɪɾ ɐlˈaʊz pˈiːpəl tʊ aɪdˈɛntᵻfˌaɪ vˈɛɹiəs lˈoːɹɪkˌæɹɪˌɪd kˈætfɪʃ baɪ ˈeɪ "kˈɑːmən nˈeɪm" bᵻfˌoːɹ ðə fˈɪʃ ɪz əfˈɪʃəli dᵻskɹˈaɪbd.