net = alexnet; % load a network
ClassIndexes = string(num2cell(1:1000)'); % indexes to string
ClassNamesWithIndexes = strcat(ClassIndexes,repmat(":",1000, 1),net.Layers(end).ClassNames); % concatenate names and indexes

disp(ClassNamesWithIndexes) % Display result

Results

1:tench 2:goldfish 3:great white shark 4:tiger shark 5:hammerhead 6:electric ray 7:stingray 8:cock 9:hen 10:ostrich 11:brambling 12:goldfinch 13:house finch 14:junco 15:indigo bunting 16:robin 17:bulbul 18:jay 19:magpie 20:chickadee 21:water ouzel 22:kite 23:bald eagle 24:vulture 25:great grey owl 26:European fire salamander 27:common newt 28:eft 29:spotted salamander 30:axolotl 31:bullfrog 32:tree frog 33:tailed frog 34:loggerhead 35:leatherback turtle 36:mud turtle 37:terrapin 38:box turtle 39:banded gecko 40:common iguana 41:American chameleon 42:whiptail 43:agama 44:frilled lizard 45:alligator lizard 46:Gila monster 47:green lizard 48:African chameleon 49:Komodo dragon 50:African crocodile 51:American alligator 52:triceratops 53:thunder snake 54:ringneck snake 55:hognose snake 56:green snake 57:king snake 58:garter snake 59:water snake 60:vine snake 61:night snake 62:boa constrictor 63:rock python 64:Indian cobra 65:green mamba 66:sea snake 67:horned viper 68:diamondback 69:sidewinder 70:trilobite 71:harvestman 72:scorpion 73:black and gold garden spider 74:barn spider 75:garden spider 76:black widow 77:tarantula 78:wolf spider 79:tick 80:centipede 81:black grouse 82:ptarmigan 83:ruffed grouse 84:prairie chicken 85:peacock 86:quail 87:partridge 88:African grey 89:macaw 90:sulphur-crested cockatoo 91:lorikeet 92:coucal 93:bee eater 94:hornbill 95:hummingbird 96:jacamar 97:toucan 98:drake 99:red-breasted merganser 100:goose 101:black swan 102:tusker 103:echidna 104:platypus 105:wallaby 106:koala 107:wombat 108:jellyfish 109:sea anemone 110:brain coral 111:flatworm 112:nematode 113:conch 114:snail 115:slug 116:sea slug 117:chiton 118:chambered nautilus 119:Dungeness crab 120:rock crab 121:fiddler crab 122:king crab 123:American lobster 124:spiny lobster 125:crayfish 126:hermit crab 127:isopod 128:white stork 129:black stork 130:spoonbill 131:flamingo 132:little blue heron 133:American egret 134:bittern 135:crane 136:limpkin 137:European gallinule 138:American coot 139:bustard 140:ruddy turnstone 141:red-backed sandpiper 142:redshank 143:dowitcher 144:oystercatcher 145:pelican 146:king penguin 147:albatross 148:grey whale 149:killer whale 150:dugong 151:sea lion 152:Chihuahua 153:Japanese spaniel 154:Maltese dog 155:Pekinese 156:Shih-Tzu 157:Blenheim spaniel 158:papillon 159:toy terrier 160:Rhodesian ridgeback 161:Afghan hound 162:basset 163:beagle 164:bloodhound 165:bluetick 166:black-and-tan coonhound 167:Walker hound 168:English foxhound 169:redbone 170:borzoi 171:Irish wolfhound 172:Italian greyhound 173:whippet 174:Ibizan hound 175:Norwegian elkhound 176:otterhound 177:Saluki 178:Scottish deerhound 179:Weimaraner 180:Staffordshire bullterrier 181:American Staffordshire terrier 182:Bedlington terrier 183:Border terrier 184:Kerry blue terrier 185:Irish terrier 186:Norfolk terrier 187:Norwich terrier 188:Yorkshire terrier 189:wire-haired fox terrier 190:Lakeland terrier 191:Sealyham terrier 192:Airedale 193:cairn 194:Australian terrier 195:Dandie Dinmont 196:Boston bull 197:miniature schnauzer 198:giant schnauzer 199:standard schnauzer 200:Scotch terrier 201:Tibetan terrier 202:silky terrier 203:soft-coated wheaten terrier 204:West Highland white terrier 205:Lhasa 206:flat-coated retriever 207:curly-coated retriever 208:golden retriever 209:Labrador retriever 210:Chesapeake Bay retriever 211:German short-haired pointer 212:vizsla 213:English setter 214:Irish setter 215:Gordon setter 216:Brittany spaniel 217:clumber 218:English springer 219:Welsh springer spaniel 220:cocker spaniel 221:Sussex spaniel 222:Irish water spaniel 223:kuvasz 224:schipperke 225:groenendael 226:malinois 227:briard 228:kelpie 229:komondor 230:Old English sheepdog 231:Shetland sheepdog 232:collie 233:Border collie 234:Bouvier des Flandres 235:Rottweiler 236:German shepherd 237:Doberman 238:miniature pinscher 239:Greater Swiss Mountain dog 240:Bernese mountain dog 241:Appenzeller 242:EntleBucher 243:boxer 244:bull mastiff 245:Tibetan mastiff 246:French bulldog 247:Great Dane 248:Saint Bernard 249:Eskimo dog 250:malamute 251:Siberian husky 252:dalmatian 253:affenpinscher 254:basenji 255:pug 256:Leonberg 257:Newfoundland 258:Great Pyrenees 259:Samoyed 260:Pomeranian 261:chow 262:keeshond 263:Brabancon griffon 264:Pembroke 265:Cardigan 266:toy poodle 267:miniature poodle 268:standard poodle 269:Mexican hairless 270:timber wolf 271:white wolf 272:red wolf 273:coyote 274:dingo 275:dhole 276:African hunting dog 277:hyena 278:red fox 279:kit fox 280:Arctic fox 281:grey fox 282:tabby 283:tiger cat 284:Persian cat 285:Siamese cat 286:Egyptian cat 287:cougar 288:lynx 289:leopard 290:snow leopard 291:jaguar 292:lion 293:tiger 294:cheetah 295:brown bear 296:American black bear 297:ice bear 298:sloth bear 299:mongoose 300:meerkat 301:tiger beetle 302:ladybug 303:ground beetle 304:long-horned beetle 305:leaf beetle 306:dung beetle 307:rhinoceros beetle 308:weevil 309:fly 310:bee 311:ant 312:grasshopper 313:cricket 314:walking stick 315:cockroach 316:mantis 317:cicada 318:leafhopper 319:lacewing 320:dragonfly 321:damselfly 322:admiral 323:ringlet 324:monarch 325:cabbage butterfly 326:sulphur butterfly 327:lycaenid 328:starfish 329:sea urchin 330:sea cucumber 331:wood rabbit 332:hare 333:Angora 334:hamster 335:porcupine 336:fox squirrel 337:marmot 338:beaver 339:guinea pig 340:sorrel 341:zebra 342:hog 343:wild boar 344:warthog 345:hippopotamus 346:ox 347:water buffalo 348:bison 349:ram 350:bighorn 351:ibex 352:hartebeest 353:impala 354:gazelle 355:Arabian camel 356:llama 357:weasel 358:mink 359:polecat 360:black-footed ferret 361:otter 362:skunk 363:badger 364:armadillo 365:three-toed sloth 366:orangutan 367:gorilla 368:chimpanzee 369:gibbon 370:siamang 371:guenon 372:patas 373:baboon 374:macaque 375:langur 376:colobus 377:proboscis monkey 378:marmoset 379:capuchin 380:howler monkey 381:titi 382:spider monkey 383:squirrel monkey 384:Madagascar cat 385:indri 386:Indian elephant 387:African elephant 388:lesser panda 389:giant panda 390:barracouta 391:eel 392:coho 393:rock beauty 394:anemone fish 395:sturgeon 396:gar 397:lionfish 398:puffer 399:abacus 400:abaya 401:academic gown 402:accordion 403:acoustic guitar 404:aircraft carrier 405:airliner 406:airship 407:altar 408:ambulance 409:amphibian 410:analog clock 411:apiary 412:apron 413:ashcan 414:assault rifle 415:backpack 416:bakery 417:balance beam 418:balloon 419:ballpoint 420:Band Aid 421:banjo 422:bannister 423:barbell 424:barber chair 425:barbershop 426:barn 427:barometer 428:barrel 429:barrow 430:baseball 431:basketball 432:bassinet 433:bassoon 434:bathing cap 435:bath towel 436:bathtub 437:beach wagon 438:beacon 439:beaker 440:bearskin 441:beer bottle 442:beer glass 443:bell cote 444:bib 445:bicycle-built-for-two 446:bikini 447:binder 448:binoculars 449:birdhouse 450:boathouse 451:bobsled 452:bolo tie 453:bonnet 454:bookcase 455:bookshop 456:bottlecap 457:bow 458:bow tie 459:brass 460:brassiere 461:breakwater 462:breastplate 463:broom 464:bucket 465:buckle 466:bulletproof vest 467:bullet train 468:butcher shop 469:cab 470:caldron 471:candle 472:cannon 473:canoe 474:can opener 475:cardigan 476:car mirror 477:carousel 478:carpenter's kit 479:carton 480:car wheel 481:cash machine 482:cassette 483:cassette player 484:castle 485:catamaran 486:CD player 487:cello 488:cellular telephone 489:chain 490:chainlink fence 491:chain mail 492:chain saw 493:chest 494:chiffonier 495:chime 496:china cabinet 497:Christmas stocking 498:church 499:cinema 500:cleaver 501:cliff dwelling 502:cloak 503:clog 504:cocktail shaker 505:coffee mug 506:coffeepot 507:coil 508:combination lock 509:computer keyboard 510:confectionery 511:container ship 512:convertible 513:corkscrew 514:cornet 515:cowboy boot 516:cowboy hat 517:cradle 518:crane (machine) 519:crash helmet 520:crate 521:crib 522:Crock Pot 523:croquet ball 524:crutch 525:cuirass 526:dam 527:desk 528:desktop computer 529:dial telephone 530:diaper 531:digital clock 532:digital watch 533:dining table 534:dishrag 535:dishwasher 536:disk brake 537:dock 538:dogsled 539:dome 540:doormat 541:drilling platform 542:drum 543:drumstick 544:dumbbell 545:Dutch oven 546:electric fan 547:electric guitar 548:electric locomotive 549:entertainment center 550:envelope 551:espresso maker 552:face powder 553:feather boa 554:file 555:fireboat 556:fire engine 557:fire screen 558:flagpole 559:flute 560:folding chair 561:football helmet 562:forklift 563:fountain 564:fountain pen 565:four-poster 566:freight car 567:French horn 568:frying pan 569:fur coat 570:garbage truck 571:gasmask 572:gas pump 573:goblet 574:go-kart 575:golf ball 576:golfcart 577:gondola 578:gong 579:gown 580:grand piano 581:greenhouse 582:grille 583:grocery store 584:guillotine 585:hair slide 586:hair spray 587:half track 588:hammer 589:hamper 590:hand blower 591:hand-held computer 592:handkerchief 593:hard disc 594:harmonica 595:harp 596:harvester 597:hatchet 598:holster 599:home theater 600:honeycomb 601:hook 602:hoopskirt 603:horizontal bar 604:horse cart 605:hourglass 606:iPod 607:iron 608:jack-o'-lantern 609:jean 610:jeep 611:jersey 612:jigsaw puzzle 613:jinrikisha 614:joystick 615:kimono 616:knee pad 617:knot 618:lab coat 619:ladle 620:lampshade 621:laptop 622:lawn mower 623:lens cap 624:letter opener 625:library 626:lifeboat 627:lighter 628:limousine 629:liner 630:lipstick 631:Loafer 632:lotion 633:loudspeaker 634:loupe 635:lumbermill 636:magnetic compass 637:mailbag 638:mailbox 639:maillot 640:maillot, tank suit 641:manhole cover 642:maraca 643:marimba 644:mask 645:matchstick 646:maypole 647:maze 648:measuring cup 649:medicine chest 650:megalith 651:microphone 652:microwave 653:military uniform 654:milk can 655:minibus 656:miniskirt 657:minivan 658:missile 659:mitten 660:mixing bowl 661:mobile home 662:Model T 663:modem 664:monastery 665:monitor 666:moped 667:mortar 668:mortarboard 669:mosque 670:mosquito net 671:motor scooter 672:mountain bike 673:mountain tent 674:mouse 675:mousetrap 676:moving van 677:muzzle 678:nail 679:neck brace 680:necklace 681:nipple 682:notebook 683:obelisk 684:oboe 685:ocarina 686:odometer 687:oil filter 688:organ 689:oscilloscope 690:overskirt 691:oxcart 692:oxygen mask 693:packet 694:paddle 695:paddlewheel 696:padlock 697:paintbrush 698:pajama 699:palace 700:panpipe 701:paper towel 702:parachute 703:parallel bars 704:park bench 705:parking meter 706:passenger car 707:patio 708:pay-phone 709:pedestal 710:pencil box 711:pencil sharpener 712:perfume 713:Petri dish 714:photocopier 715:pick 716:pickelhaube 717:picket fence 718:pickup 719:pier 720:piggy bank 721:pill bottle 722:pillow 723:ping-pong ball 724:pinwheel 725:pirate 726:pitcher 727:plane 728:planetarium 729:plastic bag 730:plate rack 731:plow 732:plunger 733:Polaroid camera 734:pole 735:police van 736:poncho 737:pool table 738:pop bottle 739:pot 740:potter's wheel 741:power drill 742:prayer rug 743:printer 744:prison 745:projectile 746:projector 747:puck 748:punching bag 749:purse 750:quill 751:quilt 752:racer 753:racket 754:radiator 755:radio 756:radio telescope 757:rain barrel 758:recreational vehicle 759:reel 760:reflex camera 761:refrigerator 762:remote control 763:restaurant 764:revolver 765:rifle 766:rocking chair 767:rotisserie 768:rubber eraser 769:rugby ball 770:rule 771:running shoe 772:safe 773:safety pin 774:saltshaker 775:sandal 776:sarong 777:sax 778:scabbard 779:scale 780:school bus 781:schooner 782:scoreboard 783:screen 784:screw 785:screwdriver 786:seat belt 787:sewing machine 788:shield 789:shoe shop 790:shoji 791:shopping basket 792:shopping cart 793:shovel 794:shower cap 795:shower curtain 796:ski 797:ski mask 798:sleeping bag 799:slide rule 800:sliding door 801:slot 802:snorkel 803:snowmobile 804:snowplow 805:soap dispenser 806:soccer ball 807:sock 808:solar dish 809:sombrero 810:soup bowl 811:space bar 812:space heater 813:space shuttle 814:spatula 815:speedboat 816:spider web 817:spindle 818:sports car 819:spotlight 820:stage 821:steam locomotive 822:steel arch bridge 823:steel drum 824:stethoscope 825:stole 826:stone wall 827:stopwatch 828:stove 829:strainer 830:streetcar 831:stretcher 832:studio couch 833:stupa 834:submarine 835:suit 836:sundial 837:sunglass 838:sunglasses 839:sunscreen 840:suspension bridge 841:swab 842:sweatshirt 843:swimming trunks 844:swing 845:switch 846:syringe 847:table lamp 848:tank 849:tape player 850:teapot 851:teddy 852:television 853:tennis ball 854:thatch 855:theater curtain 856:thimble 857:thresher 858:throne 859:tile roof 860:toaster 861:tobacco shop 862:toilet seat 863:torch 864:totem pole 865:tow truck 866:toyshop 867:tractor 868:trailer truck 869:tray 870:trench coat 871:tricycle 872:trimaran 873:tripod 874:triumphal arch 875:trolleybus 876:trombone 877:tub 878:turnstile 879:typewriter keyboard 880:umbrella 881:unicycle 882:upright 883:vacuum 884:vase 885:vault 886:velvet 887:vending machine 888:vestment 889:viaduct 890:violin 891:volleyball 892:waffle iron 893:wall clock 894:wallet 895:wardrobe 896:warplane 897:washbasin 898:washer 899:water bottle 900:water jug 901:water tower 902:whiskey jug 903:whistle 904:wig 905:window screen 906:window shade 907:Windsor tie 908:wine bottle 909:wing 910:wok 911:wooden spoon 912:wool 913:worm fence 914:wreck 915:yawl 916:yurt 917:web site 918:comic book 919:crossword puzzle 920:street sign 921:traffic light 922:book jacket 923:menu 924:plate 925:guacamole 926:consomme 927:hot pot 928:trifle 929:ice cream 930:ice lolly 931:French loaf 932:bagel 933:pretzel 934:cheeseburger 935:hotdog 936:mashed potato 937:head cabbage 938:broccoli 939:cauliflower 940:zucchini 941:spaghetti squash 942:acorn squash 943:butternut squash 944:cucumber 945:artichoke 946:bell pepper 947:cardoon 948:mushroom 949:Granny Smith 950:strawberry 951:orange 952:lemon 953:fig 954:pineapple 955:banana 956:jackfruit 957:custard apple 958:pomegranate 959:hay 960:carbonara 961:chocolate sauce 962:dough 963:meat loaf 964:pizza 965:potpie 966:burrito 967:red wine 968:espresso 969:cup 970:eggnog 971:alp 972:bubble 973:cliff 974:coral reef 975:geyser 976:lakeside 977:promontory 978:sandbar 979:seashore 980:valley 981:volcano 982:ballplayer 983:groom 984:scuba diver 985:rapeseed 986:daisy 987:yellow lady's slipper 988:corn 989:acorn 990:hip 991:buckeye 992:coral fungus 993:agaric 994:gyromitra 995:stinkhorn 996:earthstar 997:hen-of-the-woods 998:bolete 999:ear 1000:toilet tissue