Effect of Fish Removal on the Growth and Condition of White Shrimp in Brackish Ponds1

Abstract

ABSTRACTThe effect of fish removal on the growth and condition of juvenile white shrimp (Penaeus setiferus) was examined using a 0.5 and 1.0 ha pond near West Galveston Bay, Texas. Prior to stocking, the 1.0 ha pond was treated with a rotenone compound (Chem Fish Collector) at a rate of 1.0 ppm to remove fish. Those species removed were Brevoortia patronus, Myrophis punctatus, Cyprinodon variegatus, Fundulus grandis, Poecilia latipinna, Leiostomus xanthurus, Mugil cephalus, and Menidia beryllina. These species were abundant in the 0.5 ha pond. Juvenile white shrimp were stocked in both ponds at a rate of 50,000 per ha and fed a supplemental pelleted ration 3 days a week at a rate of 10% of their estimated total weight.After 77 days, shrimp in the treated pond averaged 12.3 mm longer and 4.0 g heavier than those in the pond with fish, and seine samples indicated that shrimp abundance had noticeably declined in the pond with fish. It was concluded that fish not only prey on shrimp, thus reducing their numbers, but also compete with them for supplemental and natural feeds, thus depressing their growth rate. Condition of shrimp in the treated pond was significantly better than in the untreated pond throughout the duration of the experiment, but this probably resulted because the seed stock were taken from different bay populations. In both ponds, the condition of the shrimp declined drastically during the first 8 days after stocking, but then gradually improved throughout the remainder of the experiment. The length‐weight relationship of shrimp in each pond is also presented. A comparison of these relationships confirmed that shrimp in the treated pond were in better condition throughout their entire size range than those in the pond with fish, but again, the difference could be the result of different populations of seed stock.