Zaul García-Esquivel

The use of silage made from fish and abalone viscera as an ingredient in abalone feed

Abstract Silage prepared from fish and abalone viscera are effective dietary protein sources for the juvenile abalone, Haliotis fulgens . Significantly higher growth rates occurred when abalone were fed artificial diets containing heated fish silage (53 μm day −1 ) and unheated fish silage (61 μm day −1 ) as a protein source compared with the kelp, Macrocystis pyrifera (1.5 μm day −1 ). However, no differences were found between diets containing heated and unheated fish silage at 30% protein inclusion, suggesting that the degree of hydrolysis did not affect protein utilization by abalone. Similar results were obtained when abalone viscera silage was used (50 μm day −1 ), producing faster growth rates than kelp (18 μm day −1 ) or kelp meal (12 μm day −1 ). In the same experiment a significant increase in growth rate was observed when abalone with low growth rates, resulting from feeding on kelp and kelp meal, were switched to a diet containing abalone viscera silage. These animals exhibited higher growth rates (135 and 167 μm day −1 ) than animals fed this diet throughout the trial (122 μm day −1 ), suggesting the presence of compensatory growth of organisms.

Effect of dietary protein:energy ratio on intake, growth and metabolism of juvenile green abalone Haliotis fulgens

Abstract Juvenile green abalone Haliotis rufescens were grown under laboratory conditions at 21±1 °C and fed formulated diets consisting of different protein:energy ratios (mg protein/kcal), 62, 74, 85, 100, 108, for 60 days. The level of crude protein ranged from approximately 26% to 44% while the energy content remained constant at about 4.1 kcal g −1 . Growth ranged from 3.63 to 12.33 mg day −1 . The growth of abalone fed the 100 and 108 diets was significantly greater than that of each of the other diets. Protein efficiency ratio increased as the dietary protein content increased except for the T108 diet (44% crude protein). Abalone apparently consume food to satisfy an energy requirement. Caloric expenditure due to metabolism was estimated for abalone fed diets with protein ratios of 62, 85, 100. Energy loss due to respiration did not vary appreciably among abalone fed the different diets. The proportional distribution of dietary energy into fecal, digestible, growth, and metabolic energy was estimated for abalone fed these diets. Apparent dry matter digestibility was among the lowest for abalone fed the 100 P:E diet, but growth of abalone fed this diet was significantly higher than that of each of the other treatments except the 108 diet. Unexplained energy loss to achieve balance ranged from 7% to 28.5%, some of which is probably due to differential mucus and ammonia production. Results suggest a potential for the reduction of both dietary protein and lipid without causing any adverse effects on the growth response.

Physiological basis for energy demands and early postlarval mortality in the Pacific oyster, Crassostrea gigas

Simultaneous physiological (metabolic and excretion rates) and biochemical evaluations (shell/tissue growth, protein, lipid, carbohydrate content, and enzyme activity of the electron transport system) were performed on four batches of hatchery-produced, Pacific oysters (Crassostrea gigas), in order to assess the physiological basis for metamorphic energy demands and postlarval mortality. Evaluations were carried out during normal development (0–25 days post-settlement). Despite differences in the magnitude of physiological and biochemical responses, all oyster batches exhibited a catabolic period associated with metamorphosis, followed by exponential growth. Both protein and lipid content were reduced (by 23–28%), whereas weight-specific metabolic rates (VO2), ammonium excretion rates and activity of the electron transport system (ETS) were highest during metamorphosis. Intense shell growth (13–23% day−1) continued during the same period. The cost of metamorphosis varied between 5.4 and 7.7 mJ ind−1. The effect of metamorphic stress extended throughout the first week post-settlement, as shown by high values of VO2, (112–140 μmol O2 h−1 g−1 ash-free dry weight (AFDW)), ETS activity (500–1000 μmol O2 h−1 g−1 AFDW) and cumulative mortality (14–52%). The amount of lipid or total energy present in pre-metamorphic larvae did no exert any significant effect on postlarval survival, rather protein utilization during metamorphosis appeared to be the limiting step for survival. This study provided the first evaluation of the oxygen/nitrogen atomic ratio (O/N) and ETS activity as physiological indices in early oyster stages, and questions the use of single oxyenthalpic equivalents to estimate metabolic demands during short periods of nutritional stress of bivalves. ETS activity readily reflected the metabolic condition of oyster postlarvae, and scaled allometrically with the same mass exponent (b=0.92) as VO2, therefore suggesting its potential value as an instantaneous index of oyster metabolism. Lowest O/N ratios (<15) coincided with high protein catabolism during metamorphosis, whereas increasing O/N values (up to 43) may have reflected a higher reliance on lipid metabolism with increasing postlarval age. High ratios of VO2/ETS observed during the first week post-settlement (0.15–0.35) may have also reflected an increased efficiency of the oysters mitochondrial machinery.

Diagnosis of trace metal contamination in sediments : The example of Ensenada and El Sauzal, two harbors in Baja California, Mexico

Total metal concentrations in sediments from within Ensenada and El Sauzal Harbors are generally higher than at the mouths. Grain-size analyses suggested that this enrichment could be due to the presence of fine-grained sediments in the inner part of the harbors rather than to anthropogenic perturbations. The (Me/Al)sample ratios for Pb, Co, Ni and Fe were significantly higher for Ensenada Harbor relative to El Sauzal Harbor, whereas the ratios for Cd, Mn, Zn and Cu were statistically equivalent for both harbors. Calculated enrichment factors [EFMe=(Me/Al)sample/(Me/Al)shale] indicated that the metals showing slight enrichment were those associated with anthropogenic contamination (Pb, Zn), or probably related to primary productivity in the water column (Cd, Co). The levels of most of the metals were not greatly enriched, a consideration that is of the utmost importance when contamination issues are at stake.

Metabolic depression and whole-body response to enforced starvation by Crassostrea gigas postlarvae

Physiological and biochemical measurements were performed on six oyster (Crassostrea gigas) cohorts, in order to: (a) investigate the whole-body response (growth, energy content, metabolic and excretion rates) of 2-week-old postlarvae (spat) to enforced (0-8 days) starvation, and (b) test the potential use of three aerobic enzyme systems as indices of physiological condition. Starvation resulted in exponential reduction of postlarval metabolic and excretion rates, as well as a linear decrease in enzyme activity. These response mechanisms effectively limited the loss of endogenous reserves after 2 days of starvation and maintained the oysters functional integrity over prolonged (8 days) starvation. Proteins appeared to be selectively conserved during short-term (2 days) starvation, as suggested by a decrease in total protein content, while maintaining constant weight-specific enzyme activity. Postlarvae starved for 2 days exhibited relatively higher lipid losses, lower mortality and lower metabolism than metamorphosing stages, thus suggesting a greater buffering capacity to starvation in the former. The activity of the electron transport system may be a useful indicator of long-term stress or developmental condition of oyster postlarvae, while citrate synthase and cytochrome oxidase could be used as indicators of growth rate. None of these enzyme systems is recommended as an index of aerobic metabolism during short-term starvation.

Physiological energetics of the green abalone, Haliotis fulgens, fed on a balanced diet.

A regression of different physiological responses against body size enables populations or stock cultures of various size ranges to be compared. Thus, the aim of the present work was to evaluate the physiological responses from juvenile green abalone (Haliotis fulgens), grouped according to size, in a standard controlled culture condition within their optimal range to create the balanced growth equation within an allometric relation, providing a basic framework for physiological research into H. fulgens. Feed intake, absorption efficiency, respiration and excretion were measured as functions of dry tissue weight (DTW) in juvenile abalone acclimated on a balanced diet. The daily feed intake (I) was related to body mass by the relationship I (mg day−1)=24.25W0.59. Absorption efficiency averaged 87% and was independent of body size. The equation relating daily respiration rate (R) to body mass was R (ml O2 day−1)=12.013W0.704, including night correction. The rate of ammonia excretion (U) was related to dry tissue weight by the equation U (μmol N–NH4 day−1)=43.57W0.85. The energetic value of food was 18.8 J mg−1. The low feeding activity (<1% of abalone live weight per day) was compensated for by a relatively high absorption efficiency and a depression of 23% in the metabolic rate during diurnal activity. Gross and net growth efficiencies were constant throughout the size range, with average values of 36.4% and 41.5%, respectively. Values of the O/N ratio, with an average of 31.5, showed a higher use of proteins from the diet as an energy source for the size range studied.

GROWTH, SURVIVAL, AND FEEDING RATES FOR THE GEODUCK PANOPEA GLOBOSA DURING LARVAL DEVELOPMENT

ABSTRACT Developmental larval stages of the geoduck Panopea globosa (Dall, 1898) are described for the first time. Growth rate, survival, and the length—size relationship were also assessed at 22°C in five independently reared cohorts. Clearance rates (CR), ingestion rates (IR), dry weight, and organic weight of select larval stages were quantified in two additional runs. Clearance rates and IR were evaluated as a function of cell concentration (50, 100, 200 and 300 cells/µL) of the chrysophyte Isochrysis sp. (clone T-ISO) using static systems. Conspicuous larval stages appeared after 20 h (trochophore), 24 h (straight hinge or “D”), 5–6 day (early umboned), 9–10 days (intermediate umboned), 11–12 days (late umboned), and 12–14 days (pediveliger). The larval period for P. globosa lasted between 12 days and 14 days, and the shell length recorded at settlement ranged from 332–356 µm (mean, 343 ± 4.2 µm). The overall average gross growth rate of the five larval cohorts was ∼20 µm/day. The relationship between larval shell length (in micrometers) and organic weight (in micrograms) followed a power function with an exponent value of 2.43, whereas the relationship between dry weight and organic weight was linear. Survival rate was approximately 50% in three larval cohorts and 20% in two cohorts. Clearance rates were inversely related to microalgal concentration regardless of larval size, and ranged from 0.3–1.5 µL/h (D larvae) to 15–59 µL/h (pediveliger, 330µm). On the other hand, IR increased with increasing algal concentration, and reached maximum values at 200 cells/µL, except in D-hinge larvae, which exhibited a maximum IR at all concentrations tested. At the highest concentration (300 cells/µL), premetamorphic larvae inhibited their IR. Overall, IR increased from 57–85 cells/h (D-hinge larvae) to 40- or 50-fold when larvae reached the premetamorphic stage. The current study revealed that P. globosa has a short larval period and high survival rate, and withstands a wide range of food concentrations without inhibiting its IR. Therefore, this species appears to be an excellent candidate for hatchery production.

Spore discharge in the carragenophyte Gigartina canaliculata Harvey (Rhodophyta, Gigartinales)

Carposporophytic and tetrasporophytic plants of Gigartina canaliculata Harvey were collected between 1983 and 1985 in the Pacific waters of Baja California near Ensenada. The purpose of the study was to estimate the total number of spores liberated by each phase of the life history under laboratory conditions. Observations on the spore-shedding process also were made. A high reproductive potential was found in both phases. Nearly a million spores and sometimes more were released by each plant and > 60% of the spores were discharged during the first 4 days after collection. The total number of liberated spores and the duration of the expulsion period were greater for carposporophytic plants. Alternating peaks of high and low production of spores appeared to occur ≈ 3 days in both phases during the shedding period but this pattern was not always discernible. Individual carpospores and tetraspores were shed serially with mucilage from the reproductive organs.

BIOCHEMICAL AND HISTOCHEMICAL CHANGES ASSOCIATED WITH GONAD DEVELOPMENT OF THE CORTEZ GEODUCK, PANOPEA GLOBOSA (DALL 1898), FROM THE GULF OF CALIFORNIA, MEXICO

ABSTRACT Thirty adult organisms of Panopea globosa, an endemic geoduck species from Baja California, Mexico, were collected monthly during a maturation cycle (October through January). Histological and semiquantitative histochemical changes (total lipids and carbohydrates) were assessed in gonad tissue during the maturation process. Biochemical quantification of proteins, lipids, carbohydrates, vitellogenin, and vitellin was performed on hemolymph and gonad tissues of all specimens. The theoretical diameter of oocytes was also estimated from their surface area, measured in histological sections of gonads. Five distinct gonadal stages were identified in both male and female geoducks, with previtellogenic (PVt)/early spermatogenic (ES) gonads being observed in October. Spawning took place in December/January when the temperature reached a plateau of ∼18.5°C. Oocyte diameter varied between 25.5 µm(PVt stage) and 74.8 µm during the late vitellogenic stage (LVt). The percent of lipids and carbohydrates evaluated histochemically in females closely mirrored the gonadal stages, as well as the diameter. Quantitative changes in proteins, lipids, and carbohydrates in the hemolymph did not show a clear temporal pattern, yet the level of vitellogenin increased from 16.4 (PVt stage)—47.8 µg/mL (LVt stage) and correlated with the oocyte diameter. The weightspecific content of proteins, lipids, and carbohydrates in the gonads was significantly greater during PVt and ES than the other gonadal stages, and remained relatively constant thereafter. Vitellin content mirrored the evolution of each maturation stage and correlated significantly with oocyte diameter. Vitellogenin or vitellin can be used as a reliable quantitative index of gender and degree of gonadic maturity in females. Hemolymph can be obtained readily from the pericardial cavity without affecting the performance of the organism significantly, which further makes vitellogenin a valuable, nonlethal marker for this genus.

Transcriptomic and metabolic response to chronic and acute thermal exposure of juvenile geoduck clams Panopea globosa

The Cortes geoduck Panopea globosa is a large bivalve with a high commercial value distributed from the southern Pacific coast of the Baja California Peninsula to the northern Gulf of California, inhabiting a wide range of subtropical temperatures. A new record of this species in shallower waters suggests that it can tolerate a warmer environment than previously thought. To better understand the whole-body and molecular response mechanisms to different temperatures, we assessed the metabolic rate of juvenile individuals exposed to chronic and acute thermal conditions and analyzed the transcriptomic response in ctenidial tissues. Whole-body metabolic rate measurements showed that juveniles were able to acclimate at least partially within three weeks from 20 °C (C20) to 29 °C (C29), while organisms acutely exposed to 29 °C (A29) significantly increased their metabolic rate. This was coincident with transcriptomic results, as similar gene expression patterns were found in clams chronically exposed to C29 and C20, but different from those acutely exposed to 29 °C (A29) and 31 °C (A31). High degree of expression of genes involved in DNA repair and transcription regulation were found in C29 juveniles, whereas protective genes against oxidative stress were highly expressed in A29 organisms. A high expression of genes involved in protein re-folding was also observed in A31 juveniles. In conclusion, the combined results of whole-body metabolism and transcriptomic expression patterns suggest that P. globosa juveniles have a high physiological plasticity and are well adapted to inhabit an environment with broad temperature fluctuations.