David V. Aldrich

GROWTH AND SURVIVAL OF POSTLARVAL PENAEUS AZTECUS UNDER CONTROLLED CONDITIONS OF TEMPERATURE AND SALINITY

1. The combined effects of salinity and temperature upon growth and survival of postlarvae of the brown shrimp, Penaeus aztecus, were studied under controlled conditions.2. Test salinity ranged from 27‰ to 40‰ and temperature from 7° to 35° C.3. With relatively short periods of acclimation, postlarval brown shrimp withstood wide fluctuations in both temperature and salinity for 24 hours.4. The range of tolerance to these factors over periods of 28 days was only slightly less than that observed for 24 hours.5. Postlarvae survived temperatures as low as 11° C. with almost no growth for one month in salinities of about 15‰ or above.6. Growth increased with temperature, with significant growth beginning at some temperature above 11° C. but below 18° C. The most marked increase in growth rate occurred in the temperature region between 11° and 25° C.7. At temperatures below 15° C., young (postlarval) shrimp demonstrated a decreased tolerance to low salinity. This reduced tolerance may influence the natural dist...

THE EFFECT OF SALINITY ON GROWTH OF GYMNODINIUM BREVE DAVIS

1. Bacteria-free Gymnodinium breve were exposed to media with salinity values ranging from 6.3 to 46.0%o; the best growth occurred between 27 and 37%o. These results indicate G. breve to be a relative stenohaline dinoflagellate.2. Field evidence associates high incidence of dense populations with salinity levels a few parts per thousand below those of the offshore waters of the Gulf of Mexico. Our results suggest that this field distribution does not represent a salinity requirement per se, since salt concentrations equivalent to those of the open Gulf did not inhibit growth of this organism in culture.3. No instances of optimal growth occurred in culture media with salinity levels of 24%o or less. Under equivalent estuarine conditions salinity may be a limiting factor in the natural distribution of G. breve.

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...

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.

Infection of Brown Shrimp, Penaeus aztecus Ives by Prochristianella penaei Kruse (Cestoda:Trypanorhyncha) in Southeastern Louisiana Bays

Abstract The plerocercus of the trypanorhynchan cestode, Prochristianella penaei was found to be a common parasite of commercially important shrimp (Penaeus aztecus and P. setiferus) in southeastern Louisiana. During June and July 1967, the cestode was found in 42% of 971 subadult and large juvenile P. aztecus taken weekly from different estuaries. Infection of specimens from Lake Pontchartrain varied between 18% and 50% without a definite pattern, but in Lake Borgne it rose suddenly from 38% to 88% and leveled off. In the delta complex west of the Mississippi River, it increased at a slower but more regular rate and reached a maximum of 63% in the last sampling week. Prochristianella penaei was found in 75% of 150 Penaeus setiferus obtained from Lakes Pontchartrain and Borgne on two successive weeks (July 24 to August 3) following a sharp decline in the availability of P. aztecus. Infection patterns of both species are discussed relative to the ecology of sampled areas and habits of hosts involved in the...