Thomas R. Capo

Sustained high yields of Gracilaria (Rhodophyta) grown in intensive large-scale culture

Gracilaria ferox J. Agardh was grown continuously in large, outdoor tanks under a pulse-fed nutrient regime for four years. Productivity ranged from 21.4 to 59.2 g d. wt m−2 d−1 with a mean of 39.7 g d. wt m−2 d−1 over the entire study period. Because the cultures were maintained under non-nutrient limiting conditions, productivity was regulated primarily by seasonal changes in light and temperature, which accounted for 75% of the variability of growth in algal yields. Salinity ranged from 31.0 to 36.5‰ and had insignificant effects on growth within this range. The original vegetative strain was maintained over the entire study without the need for additional supplementation from field-collected stock. Because of the pulse-fed nutrient supply, epiphytic growth on the target species was negligible (< 3% total biomass) throughout the study. The yields attained in this study rank among the highest reported for any intensively managed photosynthetic crop and demonstrate the feasibility of growing red macroalgae like Gracilaria at a sustained high yield in a large-scale, land-based culture system.

Evidence of blue marlin, Makaira nigricans, spawning in the vicinity of Exuma Sound, Bahamas

Exuma Sound is a semi-enclosed body of water bounded by islands of the Bahamas. During July 2000, sampling for larval billfish was carried out throughout the Sounds surface waters as well as in adjacent open waters of the Atlantic Ocean. A total of 99 larval billfish (Istiophoridae) was collected. Ninety of the larvae were identifiable as blue marlin (Makaira nigricans) and three as sailfish (Istiophorus platypterus). The remaining larvae were also istiophorids, unidentified to species owing to damage; no larval Xiphias gladius were collected. Larval blue marlin densities ranged from 0 to 3.4 larvae/1000 m 2 ; their sizes ranged from 3.1 mm notochord length to 22.6 mm standard length. Densities tended to be highest north-east of the Sounds central axis, especially within the two regions where exchange with the Atlantic is greatest. Mean densities tended to decrease in the direction of mean flow; mean lengths increased from 8.08 mm at the Sounds mouth to 14.7 mm standard length at its upper reaches. Length-based estimates of larval age ranged from 2.2 to 17.2 days. Given these age estimates and assuming passive surface transport, the blue marlin larvae collected were likely the result of recent spawning in waters that include Exuma Sound and may extend some 200 km south-east of its mouth. This study suggests that Exuma Sound functions as a nursery area for blue marlin, and possibly other billfish species, at least during the summer. Limited sampling just outside Exuma Sound, in the Atlantic Ocean proper, also yielded blue marlin larvae.

Larval growth, development, and survival of laboratory-reared Aplysia californica: Effects of diet and veliger density

Over the last three decades, the California sea hare, Aplysia californica, has played an increasingly important role as a model organism in the neurosciences. Since 1995, the National Resource for Aplysia has supported a growing research community by providing a consistent supply of laboratory-reared individuals of known age, reproductive status, and environmental history. The purpose of the present study was to resolve the key biological factors necessary for successful culture of large numbers of high quality larval Aplysia. Data from a sequence of five experiments demonstrated that algal diet, food concentration, and veliger density significantly affected growth, attainment of metamorphic competency, and survival of Aplysia larvae. The highest growth and survival were achieved with a mixed algal diet of 1:1 Isochrysis sp (TISO) and Chaetoceros muelleri (CHGRA) at a total concentration of 250 x 10(3) cells/mL and a larval density of 0.5-1.0 per mL. Rapid growth was always correlated with faster attainment of developmental milestones and increased survival, indicating that the more rapidly growing larvae were healthier. Trials conducted with our improved protocol resulted in larval growth rates of >14 microm/day, which yielded metamorphically competent animals within 21 days with survival rates in excess of 90%. These data indicate the important effects of biotic factors on the critical larval growth period in the laboratory and show the advantages of developing optimized protocols for culture of such marine invertebrates.

Anchor tags affect swimming performance and growth of juvenile red drum (Sciaenops ocellatus)

Swimming efficiency and growth of anchor‐tagged red drum (Sciaenops ocellatus) juveniles were compared with untagged controls. The O2 consumption of fish swimming at different speeds was measured in a Blazka‐type respirometer. Daily growth rates of tagged and untagged red drum were compared over 42 d of feeding fixed rations of live mosquitofish (Gambusia affinis) to siblings held individually in 380 L tanks. At swimming speeds of ≤1.0 body lengths per second (bl s‐1), no differences in O2 consumption were found. However, at speeds of 1.5–2.5 bl s‐1, tagged red drum O2 consumption was significantly greater (by 36–39%) than that of untagged fish (ANOVA, P<0.05), indicating a substantially impaired swimming efficiency. Daily growth rates of tagged and untagged fish also differed significantly (P < 0.02). Tagged fish grew at a mean rate of 0.95 mm d‐1 and 1.45 g d‐1, while untagged fish (controls) grew at 1.14 mm d‐1 and 1.62 g d‐1. Results suggest that internal anchor tags, which weighed less than 1% offish...

Changes in D-aspartate ion currents in the Aplysia nervous system with aging.

D-Aspartate (D-Asp) can substitute for L-glutamate (L-Glu) at excitatory Glu receptors, and occurs as free D-Asp in the mammalian brain. D-Asp electrophysiological responses were studied as a potential correlate of aging in the California sea hare, Aplysia californica. Whole cell voltage- and current clamp measurements were made from primary neuron cultures of the pleural ganglion (PVC) and buccal ganglion S cluster (BSC) in 3 egg cohorts at sexual maturity and senescence. D-Asp activated an inward current at the hyperpolarized voltage of -70 mV, where molluscan NMDA receptors open free of constitutive block by Mg(2+). Half of the cells responded to both D-Asp and L-Glu while the remainder responded only to D-Asp or L-Glu, suggesting that D-Asp activated non-Glu channels in a subpopulation of these cells. The frequency of D-Asp-induced currents and their density were significantly decreased in senescent PVC cells but not in senescent BSC cells. These changes in sensory neurons of the tail predict functional deficits that may contribute to an overall decline in reflexive movement in aged Aplysia.

Decreased Response to Acetylcholine during Aging of Aplysia Neuron R15

How aging affects the communication between neurons is poorly understood. To address this question, we have studied the electrophysiological properties of identified neuron R15 of the marine mollusk Aplysia californica. R15 is a bursting neuron in the abdominal ganglia of the central nervous system and is implicated in reproduction, water balance, and heart function. Exposure to acetylcholine (ACh) causes an increase in R15 burst firing. Whole-cell recordings of R15 in the intact ganglia dissected from mature and old Aplysia showed specific changes in burst firing and properties of action potentials induced by ACh. We found that while there were no significant changes in resting membrane potential and latency in response to ACh, the burst number and burst duration is altered during aging. The action potential waveform analysis showed that unlike mature neurons, the duration of depolarization and the repolarization amplitude and duration did not change in old neurons in response to ACh. Furthermore, single neuron quantitative analysis of acetylcholine receptors (AChRs) suggested alteration of expression of specific AChRs in R15 neurons during aging. These results suggest a defect in cholinergic transmission during aging of the R15 neuron.

Growth and Survival of Juvenile Queen Conch Strombus gigas Fed Artificial Diets Containing Varying Levels of Digestible Protein and Energy

Abstract Aquaculture methods for queen conch Strombus gigas have been established for several decades. However, there is a need to improve husbandry techniques for the grow out of juveniles. The purpose of this study was to determine the growth and survival of juvenile queen conchs fed artificial diets with increasing levels of a red alga Agardhiella sp. Agardhiella, soy protein isolate, and fish oil were increased at the expense of catfish feed, wheat flour, or both to keep the diets isonitrogenous (38% crude protein [CP]) with increasing protein to energy ratios (83–96 mg CP/kcal). Yttrium was also incorporated as an inert marker for determining the digestibility of dietary nutrients. Juvenile queen conchs were stocked at 75/m2 for a total of 16 conchs per replicate (three replicates) and were fed 125 mg of diet per conch each day for 6 months. Dietary crude protein ranged from 31% to 38%. The dietary lipid, moisture, energy, ash, fiber, carbohydrate, and yttrium in each diet were also determined. Juven...

POSTMETAMORPHIC GROWTH AND METABOLISM OF LONG-SPINED BLACK SEA URCHIN (DIADEMA ANTILLARUM) REARED IN THE LABORATORY

Postmetamorphic growth and metabolism measurements were obtained on two cohorts of laboratory-reared Diadema antillarum. The cohorts grew linearly from less than 1 mm to over 43 mm. Daily growth averaged 0.097 and 0.11 mm d−1, respectively, for the two cohorts, and was found to differ significantly. Urchin metabolism was examined by a series of simultaneous measurements of oxygen consumption and ammonium excretion over 16 days on starved juveniles ranging 16.5 to 18.3 mm. Metabolic activity under conditions of starvation was used as a test of the viability of urchins reared in the laboratory with cultured food resources. Catabolic activity differed from the first week of starvation compared to the second. Metabolic response included: (1) a 2.2-fold increase in oxygen consumption rate; (2) 50% decline in ammonium excretion rate; and (3) a 5.1-fold increase in oxygen to nitrogen ratio. These measurements are consistent with a shift from almost pure protein catabolism during the first seven days of starvation to a lipid : protein catabolic ratio of 1 : 1 after the first week. Growth and metabolism experiments of this type are seen as a first step towards optimizing laboratory culture techniques of this species.

Technical Notes: Spawning Frequency and Egg Production of Captive Spotted Seatrout

Abstract Nine mature spotted seatrout Cynoscion nebulosus (seven females and two males) were placed in a recirculating-water culture system at the University of Miami Experimental Hatchery in July 1993. Photo-period and water temperature were maintained at 14 h light: 10 h dark and 27.5°C. Spotted seatrout held in this controlled photo-thermal culture system spawned on 172 occasions between August 1, 1993, and April 22, 1994, producing approximately 168 million eggs. On average, spawning occurred every 1.5 d. The 172 spawns during the 265-d spawning period represent an average of 24.6 spawns/female or 1 spawn/female every 10.8 d. The mean volume of eggs collected per spawn was 306 mL (SD = 215). The estimated average number of spotted seatrout eggs per milliliter was 3,184 (SD = 499). The mean percentage of viable eggs per spawn was 47.5% (SD = 29). Spotted seatrout held in the constant photo-thermal regime of 14 h light: 10 h dark and 27.5°C consistently produced eggs over a 9-month period.

Total Length Estimation of Red Drum from Head Dimensions

Abstract Four head dimensions of red drum Sciaenops ocellatus were individually regressed against total length (TL) to facilitate estimation of the size of hatchery-reared fish recaptured by sport anglers. Head length, postorbital head length, snout length, and eye diameter measurements were obtained from 58 individuals ranging from 130 to 639 mm TL. Each of the head dimensions was correlated with TL, and r 2 coefficients ranged from 0.963 for eye diameter to 0.995 for head length. All of the head dimensions examined appear to be good predictors of red drum TL.