Factors affecting the occurrence of early maturing males in the protandrous pandalid shrimp Pandalus latirostris

Abstract

Some Age-0 males of the protandrous pandalid shrimp Pandalus latirostris Rathbun mature in their first year, and the proportion of these early maturing males (EMMs) in a population varies both locally and annually. Two laboratory experiments and 2 field observations were conducted to clarify the factors affecting the occurrence of EMMs. The first experiment showed that EMMs needed to grow fast until the breeding season and began producing sperm at about 14 mm carapace length. Individuals with an AMP (length of the endopod/length of the appendix masculina) value above 40 were defined as EMMs. In the second experiment, the effects of food amount, hatching date and maternal size on growth at Age-0 were examined. Food amount strongly affected the early growth. A difference in hatching date of > 2 wk caused a large difference in body size of juveniles; this difference was maintained until the breeding season 3 mo later. Large females spawned larger larvae than small females, but the size difference between larvae from large females and those from small females decreased with time. Field observations showed that at one site in Saroma Lagoon, Hokkaido, Japan, hatching occurred over a 1 mo period. In 1996/1997, we found no obvious differences of size distribution of Age-0 individuals and the occurrence of EMM as a function of location in the lagoon or year. These results may have been caused by slow growth, because water temperatures in the lagoon were much colder in 1996/1997 than during 1987 to 1995. We conclude that the occurrence of EMMs is closely related to various environmental factors in shallow waters. Therefore, the proportion of EMMs may fluctuate both locally and annually. This study shows that a small difference in juvenile growth over a short period can alter the subsequent life history of P. latirostris. KEY WORDS: Protandry · Pandalid shrimp · Growth · Maturity · Life history variationResale or republication not permitted without written consent of the publisher

Maladaptive sex ratio adjustment by a sex‐changing shrimp in selective‐fishing environments

“…b). Our previous laboratory observations showed that there was little difference in growth between immature and mature individuals at age 0 and between males or females at age 1 (Chiba, Goshima & Mizushima ; Chiba ). We therefore considered our cohort separation procedure to be reasonable for estimating the age groups of age 0, age 1 and age ≥ 2.…”

“…However, males that do not change sex at age 2, termed here as postponed‐change males (PCM), are often observed in these populations. Moreover, males at age 0 and females at age 1, termed here as early‐matured males (EMM) and early‐changed females (ECF), respectively, also occur, although their proportions are relatively low (Chiba, Goshima & Mizushima ; Chiba & Goshima ). Such life‐history variations are also common in other species of pandalid shrimps (Bergström ).…”

Response of the pandalid shrimp Pandalus latirostris to dissolved oxygen, salinity and turbidity

“…The turbidities were produced with kaorin (Kanto Chemical Co. Inc., Tokyo, Japan). In both salinity and turbidity experiments, we maintained treatment water at 18°C, which is a typical temperature in summer 12 at which low salinity and highly turbid water was observed (Ogata, unpubl. data, 2001).…”

“…To investigate the effects of DO, groups of 20 shrimps with carapace lengths (CL) of 22.5-34.5 mm were randomly chosen and transferred to aquariums (60 cm ¥ 30 cm ¥ 30 cm high) containing filtered seawater (c. 30 practical salinity units [psu]). The water temperature was increased 1∞C per 12 h from ambient temperature until it reached 21∞C, which corresponds to the highest temperature in summer, 12 at which time DO is the lowest in northern Hokkaido. 10 DO was adjusted to either 0.1, 1.0, 2.0 or 8.0 mg-O 2 /L at 21∞C by pumping air for the saturated level and an O 2 /N 2 mixture (Taiyo-Toyo-Sanso Co. Ltd, Osaka, Japan) for the other levels through a plastic lid with an inlet and an outlet.…”

Isolation and characterization of 13 polymorphic microsatellites for the Hokkai Shrimp, Pandalus latirostris

“…Though transplantation between populations is being planned to sustain shrimp stocks in some populations, this may disturb the natural population structure and genetic diversity of the shrimp, in which genetic differentiation between local populations is probably high. Since the species has no planktonic larval period and establishes discrete habitats exclusively in seagrass areas (Chiba et al 2000), the dispersal ability between local populations would be low. Therefore, local populations would be genetically very different from each other.…”