Kirk Strawn

Growth and digestibility by three sizes of Penaeus vannamei Boone: Effects of dietary protein level and protein source

Abstract Growth, survival and digestibility of Penaeus vannamei were studied in three experiments. P. vannamei averaging 4.0, 9.8 and 20.8 g were monocultured in circular fiberglass tanks (2650 l) for 30 days. Six diets having protein contents of 22, 29 and 36% and an animal: plant protein source ratio of 2:1 or 1:1 were fed ad libitum. Survival ranges for small, medium and large shrimp were 81.7–93.3, 65.6–90.0 and 65.0–80.0%, respectively, and were unrelated to diet. Growth (g/day) decreased significantly with increased size of shrimp, whereas digestibility varied independently of size. Growth by all three sizes of shrimp fed the 2:1 diet series was not significantly (α = 0.05) higher than that of the 1:1 diet series. Digestibility ranges for protein, lipid and total diet were 78.6–85.8, 45.1–64.8 and 43.9–53.8%, respectively, for small shrimp; 80.7–84.5, 52.8–63.8 and 46.9–53.0%, respectively, for medium shrimp; and 78.7–85.4, 49.2–63.2 and 41.8–58.4%, respectively, for large shrimp. Protein digestibility by small shrimp was strongly correlated with dietary protein level. Only small shrimp showed a strong correlation between protein digestibility and growth. No size exhibited a relationship between growth and either lipid or total diet digestibility. Growth of small P. vannamei appeared to be more influenced by protein level where-as growth of medium and large P. vannamei appeared to be more influenced by protein source.

Cryopreservation of Atlantic croaker spermatozoa

An artificial insemination method was standardized. The effects of various extenders, dilution ratios, cryoprotectants, equilibration times, freezing and thawing rates, and semen and egg quantities on fertilization capacity of post-thaw Atlantic croaker Micropogonias undulatus spermatozoa were examined to optimize cryopreservation procedures. Fertilization rates using NaCl, Glucose, and sucrose solutions were comparable to those achieved with more complex extenders. No fertilization was obtained when methanol was the cryoprotectant. The optimum ratio of semen to DMSO to extender was 10%: 15%: 75%. No significant difference (P<0.05) in fertilization rates was found among freezing rates ranging from −10°C/min to −150°C/min. The two-step freezing method gave a fertilization rate similar to that obtained with the conventional one-step freezing method.

Survival and Growth of the Early Stages of Gulf Killifish in Various Salinities

Abstract Hatching percentage, time of hatching, and subsequent 2.5-week growth and survival of fry of gulf killifish (Fundulus grandis) were compared at 0, 5, 10, 15, 20, 25, 30, 35, 40, 60, and 80‰ salinities. Mean hatching percentages in the 0–35‰, range, with the exception of 69.0% hatch at 10‰, were high (77.0–91.3%) and did not differ significantly. At 60 and 80‰, hatching was significantly lower (21.7 and 35.7%, respectively) than at all other salinities. Times to beginning of hatch and to median hatch were positively correlated with salinity (r 2 = 0.92). Fry growth in length was highest at 20‰ and lowest at 60 and 80‰. At all other salinities, mean final length did not differ significantly. Significantly higher mean final weight of fry was recorded at 5. 20, and 35‰ than at 0, 60, and 80‰. Mean survival of fry was significantly lower at 0 and 80‰ (60.0%) than at 5–60‰ (95.0–100.0%), with the exception of 80.0% survival at 35‰. Salinity ranges of 0–40‰ for incubation and 5–40‰ for fry growth and su...

Changes in mechanical tolerance and chilling sensitivity of red drum (Sciaenopus ocellatus) embryos during development

The effects of mechanical shock and thermal stress on red drum (Sciaenopus ocellatus) embryos at specific developmental stages were studied. The tolerance of red drum embryos to mechanical and chilling shocks depended on the embryos stage of development. Gastrulae stage was more susceptible to mechanical shock than the other developmental stages. However, a different ontogenetic tolerance pattern for chilling shock was observed. It is suggested that the embryonic developmental stage needs be considered in future studies on the cryopreservation of fish embryos.

Effects of Temperature and Salinity on Thermal Death in Postlarval Brown Shrimp, Penaeus aztecus

The brown shrimp, Penaeus aztecus, forms an important part of the commercial shrimp catch along the Texas Coast. Its value as a commercial product has stimulated interest in the biology and ecology of this penaeid shrimp. In addition, interest in shrimp mariculture has focused attention on brown shrimp as a potential organism for pond culture. Information on the effects of temperature and salinity on postlarvae would, of course, be of benefit in pond culture of these animals. Obtaining information which would be of practical value in shrimp mariculture was a primary purpose of this study. Also, as increasing production of electric power adds to the thermal loads of Texas bays, the need becomes greater for appropriate knowledge of ecological requirements of estuarine life. The life cycle of the brown shrimp has been reviewed by Williams (1965). Adults spawn in the open sea. After hatching, P. aztecus undergoes several larval stages, eventually developing into the postlarval stage. Brown shrimp enter estuaries and bays as postlarvae, moving to the shallow areas of these bodies of water. In Galveston Bay, most postlarval brown shrimp enter the bay in March and April (Baxter and Renfro 1966). Analysis of fishery data by Berry and Baxter (1969) suggests that this seasonal pattern of abundance is characteristic of the species throughout its range in the Gulf of Mexico. After a period of rapid growth in the bays, brown shrimp return to the open sea to complete their life cycle. During their postlarval stage, brown shrimp move from the sea, an area of relatively stable temperaturesalinity conditions, to the bays, where considerable fluctuations of both factors may occur. Since many postlarval brown shrimp naturally occur in bays of the northwest Gulf of Mexico, some interest has been shown in the effects of temperature and salinity on these animals. Gunter (1956, 1961) has documented the penetration of P. aztecus postlarvae into areas of very low salinity, and has concluded that survival of postlarval brown shrimp is dependent on their entering low-salinity waters. This conclusion, however, was not supported by laboratory studies of long-term survival and growth (Zein1 This research was supported in part by National Science Foundation Sea Grant Program Institutional Grant GH-59 and Texas Agricultural Experiment Station Grant S-4011. This report includes a portion of the senior authors thesis, accepted by the Graduate School Faculty of Texas A & M University in partial fulfillment of the requirements for the degree of Master of Science.

Community Structure of Macrozooplankton in Trinity and Upper Galveston Bays

Macrozooplankton were sampled bi-weekly from October 1969 through May 1973 at 16 stations. Hydrological measurements, including water temperature and conductivity, accompanied each biological sample. Sampling sites and species were grouped by cluster analysis using Camberra-Metric measure of dissimilarity and flexible sorting. Two major seasons, based on taxon composition and abundance, were identified: A warm season (average water temperature above 22°C) dominated by larval and juvenile crustaceans, and a cool season with an abundance of larval fishes. Sites were more similar to each other within a year than they were between years. Differences between years correlated with variations in salinity and temperature. Community structure indices (Shannon-Weaver diversity, species richness and “evenness”) were applied to the seasonal data. Shannon diversity and “evenness” were positively correlated with each other, but richness values were often negatively correlated with the other two indices.

Air Incubation of Eggs of the Gulf Killifish

Abstract Effects of air incubation on egg hatchability and subsequent fry growth of gulf killifish (Fundulus grandis) were examined in the laboratory. Mats with approximately equal coverage of pond-spawned eggs were kept moist at a temperature of 22°C. First hatch of eggs transferred from mats to water occurred at 19 d postspawning. Total hatching occurred in 24 h, with 90% hatching in 2 h. After 31 d of air incubation, deaths of hatched fry were first noted. Air incubation on mats was terminated at 36 d. Laboratory-spawned eggs were incubated on moistened filter paper in a sealed container at 26°C. Air incubation periods were 0, 6, 12, 18, and 24 d. For eggs with 0 d and 6 d air incubation, hatching occurred 8–11 d after they were spawned. Eggs incubated in air for 12 d and longer hatched after 30 min in water. Mean survivals were significantly higher in the 6- and 12-d groups (95 and 92%) than in the 0- and I8-d groups (85 and 83%). All of these survival values were significantly higher than in the 24-d...

Notes on the River Shrimp, Macrobrachium ohione (Smith) 1874, in the Galveston Bay System of Texas

Abstract The migration of Macrobrachium ohione during its spawning season was observed from 1969 to 1971 in the Galveston Bay area. Maximum activity was at night and during the new moon. Rainfall seemed to be associated with increased movement. Salinities near 15 ‰ appeared to act as a barrier to movement of this species into the Galveston Bay system.

Vertical responses of Atlantic croaker to gas supersaturation and temperature change

Abstract Vertical responses of juvenile Atlantic croakers (Micropogon undulatus) to acute supersaturation of nitrogen and oxygen and to changing temperature were observed in a 2.5-m-tall test cylinder supplied with flowing estuarine water. Supersaturation of nitrogen caused an initial upward movement of fish, although a compensatory downward response seemed to occur after 2–4 hours of exposure. Supersaturation of oxygen resulted in an almost immediate downward movement of fish. Abrupt upward displacement of fish followed water-temperature changes, especially increases. Similarities between the behavior of croakers in these experiments and the behavior of other physoclists after swim-bladder volume manipulation suggested that gas supersaturation caused the swim bladders of our fish to inflate, resulting first in upward drift and then in downward swimming to restore neutral buoyancy. A nonlinear response model incorporating this hypothesis accounted for 62% of the variation (over all experiments) in mean ve...

Annual Cycle of Sportfishing Activity at a Warmwater Discharge into Galveston Bay, Texas

Abstract A survey of sportfishing activity at the P. H. Robinson Generating Station discharge into Galveston Bay, Texas was taken from 21 October 1968 through 8 November 1969. During 108 daily checks, 1,063 fishermen were interviewed and 2,635 fish counted. Fishing activity was related to season and temperature of the heated effluent. Maximum fishing pressure and largest catches occurred during the period December 1968 through April 1969 and November 1969 when discharge water temperatures and flow rates were minimum. Lowest angling activity and catch rates were recorded from June through September 1969 when water temperatures approached 40 C in the upper part of the fishing area. Atlantic croaker, Micropogon undulatus; sea catfish (hardhead), Arius felis; sand seatrout, Cynoscion arenarius; black drum, Pogonias cromis; red drum, Sciaenops ocellata; and spot, Leiostomus xanthurus, in order of decreasing abundance, accounted for 96.7% of the fish counted during the study. Seine, trawl, and trammel net data ...