Robert Okazaki

Weber State University · Department of Zoology

The brine shrimp Artemia exhibits two reproductive modes. 1). oviparity, producing diapause embryos; an. 2). ovoviviparity, producing free-swimming nauplii. Previous studies have suggested the existence of a critical stage that determines the reproductive mode. Physicochemical factors, such as photoperiod, temperature, and salinity, have been sugge...

Intertidal ribbon worms in the phylum Nemertea live in environments where temperature and salinity can vary widely depending on the tidal fluctuations. Heat shock proteins (Hsps) are expressed by cells in their physiological responses to these changing abiotic factors. To understand the role of Hsps, the presence of Hsp70 and Hsp90 was determined b...

Tachykinins (TKs) are a family of neurotransmitters that function as signaling molecules for such processes as maintaining homeostasis, regulating stress response, and modulating pain. TKs require the expression of at least one of three receptor subtypes: Neurokinin Receptor-1 (NKR-1), Neurokinin Receptor-2 (NKR-2), or Neurokinin Receptor-3 (NKR-3)...

Of the 14 nominal species that are now or have ever been assigned to the genus Paranemertes Coe, 1901 , four have been reported to have stylets with a spirally fluted or braided appearance. Although differentiation in color patterns has been documented among species/populations, these nemerteans share similar external characters. Using the sequence...

Artemia nauplii are important bait or food sources in aquaculture, but the egg shells after incubation are always subjected to discarding as natural wastes; therefore, application and utilization of the Artemia egg-shell wastes will be an important issue. Herein, we reported a new hybrid biomaterial by encapsulating nano-Mg(OH)(2) onto discarded Ar...

The possible presence of egg predators in brood masses of portunid crabs from Pacific Central America has not been studied yet. This survey reports the finding of a nemertean crab egg predator on the portunid crab, Callinectes arcuatus, from the Golfo de Nicoya, Pacific Costa Rica. Nemerteans were found in the egg masses of 26 out of the 74 crabs f...

Carcinonemertes epialti had a minimal impact on the egg mortality of a lightly infested population of a commercially important crab host, Cancer anthonyi. The nemertean had a high prevalence (> 97%) but was found at low intensities (mean intensity = 86.5 worms/pleopod, mean density = 0.3 worms/1000 eggs). Egg mortality varied from 0.0–30.5%, and wa...

Artemia resting eggs are well-known to be extremely tolerant to harsh conditions. However, eggs from some hypersaline waters in Qinghai–Xizang Plateau (Q-XP) have recently been reported to be very sensitive to high temperatures. Thus, the thermotolerant capacity of Artemia eggs from four hypersaline waters [(Gai Hai (GH), Aqqikkol Hu (AQK), Xizang...

Nemerteans can experience fluctuating salinity during exposure to low tides in intertidal mudflats. This study attempted to determine if stress proteins (SPs) can be induced in nemerteans exposed to fluctuating salinities under laboratory conditions. Paranemertes peregrina Coe 1901 were collected from intertidal mudflats. The ribbon worms were then...

Nemerteans experience varying environmental temperatures during low tide exposures. Inducible heat shock proteins (hsps) have been reported for most organisms following both artificial heat stress and natural environmental temperature variations. This preliminary study reports the presence of hsps in the phylum Nemertea. A lethal temperature of 36...

Ecdysteroids are a class of steroidal hormones thatare important in molting and reproduction inarthropods. These hormones have been recentlydetected in non-arthropodan groups, such assoft-bodied worms. To continue our efforts todetermine the presence of ecdysteroids in nemerteans,this study further documents the identification of20-hydroxyecdysone...

The effects of eyestalk ablation on integumental growth were examined at the cellular level in larval and adult grass shrimp, Palaemonetes pugio. Eyestalk removal of larval shrimp resulted in molt increments ranging 9-15% compared to the 7-10% for the intact larvae. Eyestalk-ablated larvae showed a 12-25% lower cell density at postmolt compared to...

Ecdysteroids in non-reproductive, reproductive, and post-reproductive specimens of two nemerteans, Paranemertes peregrina and Pantinonemertes californiensis, were studied using radioimmunoassay (RIA). Ecdysteroid concentrations increased during the reproductive season in females of both species. These data suggest the possibility that ecdysteroids...

Ecdysteroids in the embryos and sera of ovigerous brachyuran crabs, Cancer magister and C. anthonyi, were measured and characterized by radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC). C. magister embryos displayed a biphasic pattern of ecdysteroid fluctuation during development; titers decreased until mid embryogenesis and...

Ovigerous crabs carried an estimated 0.73-3.30 million eggs, depending on crab size, stage of egg development, and season. Estimates of reproductive potential (total number of eggs produced throughout the entire adult life span) were 14.7-29.4 million eggs, higher than other members of the genus. -from Authors

Ecdysteroids were detected in the phylum Nemertea and their physiological role was studied. Radioimmunoassay (RIA) measurements showed ecdysteroid concentrations ranging from 1–47 pg/mg wet weight in several nemertean species from the orders Palaeonemertea, Heteronemertea, and Hoplonemertea. High-performance liquid chromatographic (HPLC) analysis o...

This report contains the results of an investigation of the potential toxic effects of the jet fuel JP-4 (petroleum-based and shale-based) on the aqueous environment. Composition of different JP-4 samples and their water extracts are compared. Techniques for the formation and analysis of water soluble extracts of JP-4 are described together with pr...

The depuration of 12 trace metals in the mantle, gill, digestive gland, and kidney of Crassostrea gigas and C. virginica was investigated under natural field conditions; oysters from a relatively contaminated environment (Redwood Creek in south San Francisco Bay) were transplanted to a relatively clean environment (Tomales Bay). In the transplanted...

It was determined by means of light and electron microscopy that the granular blood cells of Pacific oysters could absorb basic dyes from dye-coated plastic beads injected into the mantles of oysters; in doing so, the granular blood cells became altered morphologically and behaviorally. In addition, it was observed that oysters could absorb the bas...

A laboratory study was designed to determine the lethal concentration of Cu to the Pacific oyster. Oysters 18 to 24 months old and sexually mature were held in running unfiltered sea water (33 percent), pH8, at 12 to 15/sup 0/C for one week prior to testing. The oysters were exposed to Cu concentrations of 0.10, 0.25, 0.50, 0.75, and 1.00 ppM for t...