The Status of Spotted Seatrout (\u3ci\u3eCynoscion nebulosus\u3c/i\u3e) As a Technologically Feasible Species for U.S. Marine Aquaculture

Culture models and facilities for large-scale, commercial production of popular Gulf of Mexico species are unavailable. The spotted seatrout (Cynoscion nebulosus) is one of the most popular recreational fishes in the Gulf of Mexico. Seatrout culture techniques were adapted from red drum (Sciaenops ocellatus) protocols developed in the 1970s. Broodstock husbandry, spawning, and extensive pond rearing techniques using fertilized and bloomed brackish ponds were well-established by the 1980s. By 2018, approximately 80 million 25–30-day old seatrout had been produced, mainly for stock enhancement. Cannibalism and poor nutrition hindered intensive tank culture. Between 2005 and 2015, an intensive tank-rearing protocol that reduced cannibalism and intracohort variability and increased average survival to almost 50% was developed using algal concentrate, rotifers, brine shrimp (Artemia sp.), and microencapsulated feeds. Preliminary results suggested that a 500 g fish could be produced in approximately 10 months. Nevertheless, interest in commercialization has remained low. Zootechnical performance throughout the latter stages of culture, the economics of production, consumer preferences/perceptions, and market capacity must be documented to complete the assessment of the spotted seatrout as a species for commercial aquaculture. The optimization of aquafeeds specific for seatrout and a domestication program is warranted to further facilitate industry growth

Fecundity and Survival of the Calanoid Copepod \u3ci\u3eAcartia tonsa\u3c/i\u3e Fed \u3ci\u3eIsochrysis galeana\u3c/i\u3e (Tahitian Strain) and \u3ci\u3eChaetoceros mulleri\u3c/i\u3e

Historically, red snapper (Lutjanus campechanus) larviculture at the Gulf Coast Research Lab (GCRL) used 25 ppt artificial salt water and mixed, wild zooplankton composed primarily of Acartia tonsa, a calanoid copepod. Acartia tonsa was collected from the estuarine waters of Davis Bayou and bloomed in outdoor tanks from which it was harvested and fed to red snapper larvae. We are developing a more controlled copepod mass culture system to support finfish larviculture. To that end, I examined the effect of single species versus mixed species of algae as food for the copepods. Wild A. tonsa were isolated and reared in a controlled environment. Diets used for culture of A. tonsa were T- Iso (Tahitian strain Isochrysis galbana) and Chaetoceros (Chaetoceros mulleri). Mated female copepods (n=lOO) were isolated from the laboratory population and placed individually in 10-ml containers. Twenty-five were fed T-Iso only at a cell density of300,000 cells/ml, 25 were fed C. mulleri only at a cell density of 300,000 cells/ml, and 25 were fed a mixture of both T-Iso and C. mulleri at a cell density of 150,000 cells/ml each and 25 were fed no algae. Eggs were collected and counted to quantify fecundity over a 72-hour period. The experiment was repeated. Fecundity was higher in the mixed diet treatment where 17 of the 25 female A. tons a survived ( 68% survival) and produced a total of 520 eggs. Fecundity of A. tonsa in the small-scale experiment fell within the published range of20-150 eggs/female/day for all the treatments offered a diet. Egg production in treatments receiving a mixed diet was higher than production from any of the single diet fed treatments in all small-scale experiments. Production in the unfed treatment was significantly lower (p\u3c0.05) than in all small-scale experiments. Diet did not affect survival (p\u3e0.05) in any fed or unfed treatments over the 72-hour duration of the experiments. In a larger scale experiment, a total of 20, !-liter beakers involving 5 replicates per treatment were used. Copepod density, algal density, water temperature, and salinity were the same as in the small-scale experiments. This larger scale experiment also was replicated. Individual egg production for the larger scale system fell within the published range of20-150 eggs/female/day for the algal fed treatments. Individual production in the unfed control was below 3 eggs/female/day. The hatch rate of eggs produced from a larger scale experiment was not significantly different between treatments indicating that diet had no effect on the hatch rate and that eggs produced from the experiment were fertile. Overall, the copepods produced eggs at a rate comparable to both published results and previous experiments at GCRL in all the algal fed treatments while few eggs were produced in the unfed controls. However, egg production was more consistent in the mixed diet than in the single species diet both when the copepods were tested singly and in a larger scale. There was no effect of diet on survival within each experiment when the copepods were tested singly and no effect of time on egg production. Between experiment, variability may be attributed to variability in algal quality, specifically in single diet treatments

Short-term Effects of First-prey Type and Number on Survival and Growth of Intensively Cultured Spotted Seatrout, \u3ci\u3eCynoscion nebulosus\u3c/i\u3e (Sciaenidae), Larvae

Five test diets - 20, 10 rotifers/mL/d, 5 rotifers/mL/d + 3 nauplii/mL/d, 5 and 8 nauplii/mL/d - were used to examine the effect of Acartia tonsa nauplii and a small strain of rotifers on survival, myotome height, notochord length, and condition (myotome height/notochord length) of spotted seatrout, Cynoscion nebulosus, larvae through 6-d posthatch (PH). Diet did not affect survival. Larvae fed 5 and 8 nauplii/mL or 5 rotifers + 3 nauplii were longer, taller, and in better condition than larvae fed either 10 or 20 rotifers/mL. The condition of larvae fed diets with nauplii declined after Day 5 which suggests a shortage of prey in those diets after Day 4 or 5. Although copepod nauplii offer substantial short-term benefits in the culture of spotted seatrout, further study is required to determine the number of nauplii and/or rotifers necessary in the diet beyond Day 4 and to assess the long-term impact of the different diets

An Intensive, Large-Scale Batch Culture System to Produce the Calanoid Copepod, \u3ci\u3eAcartia tonsa\u3c/i\u3e

A major obstacle to the development of hatchery production for juveniles of many marine species is the difficulty in successfully feeding early larvae. Copepods contribute to the natural diet of most marine fish larvae and feature characteristics ideal for early larval feeds including small size and suitable nutrient content. However, the use of copepods as larval feeds is limited by the inability to consistently produce them in sufficient quantities to support large-scale fish culture. Here, an innovative design for an intensive, indoor batch culture system to produce the calanoid copepod Acartia tonsa (Dana 1849), a prime candidate for use as a live food item, is described. The system features integrated grow-out and egg-production units that can be operated sequentially by 2.5 full-time employees to produce a predictable daily output of nauplii for use as live feed. The system output was on average 22 million eggs d−1 (21,955,420 ± 8,709,668) with an average hatch rate of 49% (49.1 ± 14.8) over three seasons

A Histological Study of Gametogenesis In Captive Red Snapper \u3ci\u3eLutjanus campechanus\u3c/i\u3e

Gametogenesis was monitored histologically in wild-caught red snapper (Lutjanus campechanus, Poey) maintained in captivity under simulated natural photothermal conditions. Gonads were collected every 2–3 weeks (average n = 14) for histology during the pre-spawning season (February to May, temperature increasing from 16°C to 24°C). Primary vitellogenic oocytes were first observed in one female when temperature reached 20°C. Subsequent samples revealed females in pre-vitellogenesis or at early stages of vitellogenesis, although one female had tertiary vitellogenic (Vtg3) oocytes. The first histological signs of spermatogenesis were observed when temperature reached 17°C. Spermatozoa were observed in testicular lobules of all males sampled on 14 May (24°C) but little or no sperm was released during manual stripping. Ten males and 10 females were left in tanks and monitored for spawning. No egg release was observed during the monitoring period that encompassed the natural spawning season of wild red snapper. Ovarian biopsies taken during the late spawning season (16 July) revealed that four of eight sampled females had Vtg3 oocytes. Males were manually stripped but released no sperm. These results indicate that captive red snapper can complete gametogenesis in photothermal controlled systems. Additional research is needed to develop procedures that will achieve reliable maturation and spawning