Progress in Controlled Breeding of Summer Flounder, Paralichthys dentatus, and Southern Flounder, P. lethostigma

ABSTRACT The sum mer floun der, Paralichthys dentatus, and the south ern floun der, P. lethostigma, are high value flat fish spe cies and im -por tant can di dates for com mer cial aquaculture in the east ern U.S. Wild-caught adults of both spe cies have been spawned ei ther nat u rally or by hor mone-in duc tion dur ing their first year in cap tiv ity, but spawn ing suc -cess and fre quency of vo li tional spawnings im proves with size/age and ha bit u a tion (>1.5 year) to cap tiv ity. Con trolled-en vi ron ment tanks (2.5-10 m3) sup plied with re cir cu lat ing sea wa ter (32-36 ppt) are used for photo -thermal con di tion ing of broodstock to fa cil i tate en vi ron men tal con trol, ob ser va tion, han dling, and feed ing. Stocking den si ties of 1.7-4.11 kg/m3and sex ra tios of 1-2 males:1 fe male are rec om mended, but op tima have not been de ter mined. In the sum mer floun der, com mer cial hatch er ies use hor mone-in duced spawn ing of photothermally con di tioned fish to sup -ply fingerlings year round. In tra mus cu lar im plan ta tion of a slow-re lease LHRHa pel let (dose ∼100 μg/kg) into fe males with max i mum fol li cle diameters >500 μm or with mean oocyte di am e ters rang ing from 258-456 μm in duces re pet i tive ovu la tion and spawn ing. Com mer cial culturists pres ently opt for strip spawn ing, us ing a “light ta ble” to es ti -mate time of ovu la tion, but hor mone-in duced vol un tary spawn ing and nat u ral spawn ing with out hor mone in duc tion could be come more prev a -lent with lon ger-term ac cli ma tion and do mes ti ca tion. In the south ern floun der, im plan ta tion of a slow-re lease LHRHa pel let (∼100 μg) has also in duced re pet i tive ovu la tion and spawn ing, al low ing mul ti ple strip spawn ing or vo li tional spawn ing in fe males with max i mum fol li cle di -am e ters > 500 μm. Large num bers of vi a ble em bryos have also been pro -duced through nat u ral spawn ing with out hor mone in duc tion. Through photothermal ma nip u la tion, the nat u ral spawn ing pe riod has been ex -tended by 2-3 months, but ad di tional stud ies are needed to pro duce fingerlings year round. A fun da men tal prob lem in the con trolled re pro -duc tion of both the sum mer floun der and south ern floun der is the vari -abil ity in num ber of eggs and the fer til ity rates among fe males and among con sec u tive spawns from the same fe male. More pre dict able rates of ovu la tion, as well as of fer til iza tion and hatch ing, are needed to lower costs of seed pro duc tion. Vari able spawn ing suc cess can be at trib -uted in large part to in con sis tent male per for mance and in ad e quate spermiation. Hor mone treat ments used to in duce ovu la tion in fe males have been in ef fec tive in in duc ing spermiation in males, and al ter na tive ther a pies are needed. In fe males, egg qual ity may pre sum ably be im -proved by op ti miz ing nutri tions, en vi ron men tal con di tion ing, and hor -mone doses and re lease rates. To date, adult broodstock are ob tained from the wild, and the po ten tial for se lec tive breed ing or for pro duc ing interspecific hy brids re mains un tapped.