Runtdeformity syndrome (RDS) is an economically significant, frequent disease problem of cultured Penaeus vannamei. RDS is characterized by variable, often greatly reduced, growth rate of up to 30% of a cultured population and many shrimp with cuticle deformities of the rostrum, anterior appendages or other parts. The cause of RDS is undetermined.Nursery trials comparing histologically IHHN‐positive and histologically IHHN‐negative Penaeus vannamei cultured under identical conditions were conducted at The Oceanic Institute. The IHHN‐positive populations developed RDS symptoms including increased individual size variation, reduced population growth, and high prevalance of rostrum, antennae or cuticle deformity, while the IHHN‐negative groups displayed none of these symptoms. No other diseases or parasites were identified in the IHHN‐positive populations that would account for the RDS symptoms.A single commercialele nursery was stocked with histologidly IHHN‐positive P. vannamei and a high prevalence of RDS was observed. Shrimp growth was bimodal with a subpopulation growing normally and a subpopulation growing slowly. Significant relationships between shrimp harvest size and IHHN prevalance, selected individual organ IHHN severity grades and IHHN severity index (six organs evaluated) were found. Large, apparently normal shrimp were less severely infected with virus and did not display any cuticle deformities.In sum, these data provide epidemiological and histopathological evidence for the hypothesis that infection by IHHN virus is the cause of RDS in cultured P. vannamei.

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Induction of ovarian maturation in Penaeus vannamei, by implantation of ganglion prepared from female lobster, Homarus americanus, with developing ovaries was investigated under tank culture conditions. Four of six females with thoracic ganglion implants were maturing while only two of thirteen females of the control groups with abdominal ganglion or no implant matured. Two ripe stage V were found 18 days after implantation of lobster's thoracic ganglion. This indicates that ovarian maturation of P. vannumei in tanks can be induced and accelerated by implantation of thoracic ganglion prepared from maturing females of another species. Ovarian maturation may be induced by a gonad‐stimulating hormone, secreted by the thoracic ganglion of maturing females. This gonnd‐stimdating hormone is not species specific in activity in the shrimp and lobster.

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Gut bacteria may contribute significantly to the growth and survival of cultured shrimp, although little is known about factors that affect bacterial community structure in shrimp guts. The objective of this study was to determine the abundance and species composition of gut bacteria in juvenile white shrimp Litopenaeus vannamei reared in two different environments. Eight 120‐L tanks were stocked at a density of 8 shrimphank. Two treatments were tested for 10 d and consisted of tanks receiving flow‐through water from one of two sources: 1) well water pumped from a sea‐water aquifer (Well treatment), and 2) pond water pumped from an intensive shrimp pond (Pond treatment). Shrimp mid‐ and hindguts were excised on days 1, 3, 6, and 10 for enumeration of gram‐negative, aerobic bacteria by quantifying colony‐forming units (CFU) using standard microbiological plating techniques. Identification of bacterial isolates was made using the Biologa® GN Microplate system. Bacterial numbers were significantly greater (P > 0.05) in Well shrimp than in Pond shrimp on days 1 and 3. Following day 3, a decrease in bacterial numbers occurred in the Well shrimp, and no significant differences between treatments were observed on days 6 or 10. Guts from Well shrimp were dominated by Vibrio and Aero‐monas, and these two genera accounted for 80–851 of the bacteria on each sampling day. Guts from Pond shrimp exhibited a greater bacterial diversity and were dominated by Vibrio, Aeromonas, and Pseudomonas. Flavobacterium were identified in the guts of Pond shrimp on days 3 and 10, but were not identified in any of the Well shrimp. A greater understanding of gut bacteria‐shrimp interactions could lead to increased production and profitability for shrimp farmers through the development of more cost‐effective feeds and novel disease control strategies.