Principle Investigator:

2 Abstract: In this collaborative research project, we formed a partnership of commercial fisherman and scientists from UNH and NYU to investigate stock definitions for Atlantic cod using DNA markers. Cod in U.S. waters are currently managed as two stocks: 1) a Gulf of Maine stock and 2) a Georges Bank and south stock. This designation is decades old and warrants reevaluation in light of concerns that fisheries management units may not reflect biologically meaningful population units. To address this, we used 10 microsatellite and 6 SNP markers to characterize the population genetic structure of cod in U.S. waters. We found significant differentiation among temporally and spatially divergent populations of cod (global F ST = 0.0044, G ´ ST = 0.0144), primarily stemming from two non-neutral loci, and strong evidence for a population structure that contradicts the current two-stock management model. Our results indicate that cod in U.S. waters are broadly structured into three groups: 1) a northern spring spawning coastal complex in the Gulf of Maine (GOM), 2) a southern complex consisting of winter-spawning inshore GOM, offshore GOM and sites south of Cape Cod, MA, and 3)

Effects of Partial Replacement of Fish Meal Protein by Microalgae on Growth, Feed Intake, and Body Composition of Atlantic Cod

A feeding trial was conducted with juvenile Atlantic cod Gadus morhua (initial mean weight, 40.7 g) in which a combination of dried Nannochloropsis sp. and Isochrysis sp. replaced fish meal protein in isonitrogenous, isocaloric diets. Three experimental diets (55% protein, 16.5% fat; calculated gross energy = 5,328 kcal/kg) were formulated to replace 0, 15, or 30% of dietary fish meal protein. At the conclusion of the 84-d study, no differences in survival, feed conversion ratios, viscerosomatic indices, and n-3 and n-6 fatty acids in the muscle were found among the treatment groups. Feed intake and growth, which were proportional to the level of algal incorporation, were significantly reduced in the algae-fed fish and were probably due to palatability problems. Feed intake improved in the fish fed the diet with 15% fish meal protein replacement as the study progressed, but hepatosomatic indices indicate that those fed the diet with 30% replacement were approaching starvation

Changes in gonadal hormones during oocyte development in the striped bass, Morone saxatilis

Wild striped bass, Morone saxatilis, were collected from coastal waters and spawning areas to describe the endocrine correlates of oocyte development in non-captive, migratory fish. The fish were classified according to their most advanced oocytes. Serum levels of estradiol (E2), testosterone (T) and 17α-20β-dihydroxyprogesterone (DHP) were measured by radioimmunoassay (RIA). Females in the primary growth phase and early secondary growth phase (pre-vitellogenic) had low levels of plasma steroids, ovarian lipid content and gonadosomatic indices (GSIs). Significant increases in E2, T, ovarian lipid content and GSIs occurred during the vitellogenic phase. Maximum levels of all reproductive parameters were found in prespawning fish sampled in the Hudson River. Mean levels of E2, T, ovarian lipids and GSIs for these fish were 2.0±0.5 ng/ml, 3.0±0.3 ng/ml, 24±1 mg/g, and 5.6±0.3% (mean±SEM), respectively. In fish induced to spawn with human chorionic gonadotropin (HCG), DHP levels (1.9±0.4 ng/ml) were significantly elevated. Similar levels were found in two fish captured during the spawning season, suggesting that DHP may serve as the maturation-inducing steroid in this species. © 1991 Kugler Publications, Amsterdam/Berkeley

Characterizing ovarian gene expression during oocyte growth in Atlantic cod (Gadus morhua)

Vertebrate oocytes undergo dramatic changes during development as they accumulate many RNA transcripts, glycoproteins, and yolk proteins, necessary to ensure proper fertilization and embryogenesis. Oogenesis in teleosts often requires several years for completion, but very little is known about the early developmental stages. Recently, two-stage gene expression comparisons were made during oocyte growth in coho salmon (Oncorhynchus kisutch) and Atlantic cod (Gadus morhua), but more broad-scale, comprehensive assessments have not been conducted. The objectives of the present study were to characterize the gene expression patterns throughout oocyte growth in cod and compare them to changes previously identified in coho salmon. A quantitative PCR survey was conducted using 50 genes at six ovarian stages, ranging from the onset of primary growth (oocyte differentiation) to late vitellogenesis. Most expression patterns could be grouped into three major clusters, consisting of oocyte-derived (cluster 1) and likely follicle cell (clusters 2 and 3) genes. Oocyte genes were elevated during primary growth, while many follicle cell transcripts were abundant during oocyte differentiation and vitellogenesis. Few expression changes identified in coho salmon were evident in cod, which is likely due to differences in reproductive strategies. These results demonstrate that dynamic changes in gene expression occur during oocyte growth in teleost fish

Identification of ovarian gene expression patterns during vitellogenesis in Atlantic cod (\u3ci\u3eGadus morhua\u3c/i\u3e)

Follicular maturational competence and ovulatory competence in teleost fish refer to the ability of the ovarian follicle to undergo final oocyte maturation and ovulation, respectively, in response to gonadotropin stimulation and other external cues. Some gene products related to competence acquisition are likely synthesized during vitellogenic growth, as these follicles gain in vivo responsiveness to exogenous gonadotropin stimulation and can be induced to undergo maturation and ovulation. In Atlantic cod (Gadus morhua), gonadotropin responsiveness has been shown to be oocyte size-dependent, and only ovaries containing late-stage vitellogenic follicles can be induced to ovulate. The purpose of the present study was to compare gene expression patterns between mid (unresponsive) and late (responsive) vitellogenic ovaries to identify genes involved in gonadotropin responsiveness and the acquisition of maturational and ovulatory competencies. Representational difference analysis was conducted in two reciprocal comparisons using intact ovarian fragments and follicle wall-enriched tissues, and genes of interest were used in real time quantitative PCR to confirm differential expression. Few differences were detected in intact ovarian fragments, but type IV ice-structuring protein and gephyrin were upregulated later in development and may be involved in lipid and sulfur metabolism, respectively. Candidate gene assays for luteinizing hormone receptor and aromatase also exhibited significant upregulation during vitellogenesis. Many genes were differentially expressed in follicle wall-enriched tissues, including endocrine maturational regulators and smooth muscle genes. Overall, maturational and ovulatory competencies during vitellogenesis in Atlantic cod are associated with up- and downregulation of many genes involved in lipid metabolism, endocrine regulation, and ovulatory preparation

Induced sex change in black sea bass

Experiments were conducted to identify factors involved in sex change in the protogynous black sea bass Centropristis striata. Black sea bass maintained in the ratio of 8 females (F):0 males (M) for 9 months reversed sex while those kept at the ratios of 6F:2M or 4F:4M did not. Female black sea bass implanted with 1.0 mg 11-ketotestosterone (11-KT) or 10 mg fadrozole (FAD) changed sex and began spermiating while those implanted with 0.1 mg 11-KT or 1.0 mg FAD underwent incomplete sex reversal. One fish implanted with 1.0 mg FAD initiated sex change but was not spermiating at the end of the study. One fish in the control group, the largest fish in the study, initiated sex change. These results suggest that the presence of males may restrict sex reversal in black sea bass and that high 17 beta-oestradiol:11-KT is required for maintaining ovarian function. (c) 2006 The Authors Journal compilation (c) 2006 The Fisheries Society of the British Isles

Effect of acclimation temperature on the acute stress response in juvenile Atlantic cod, Gadus morhua L., and haddock, Melanogrammus aeglefinus L.

Juvenile Atlantic cod (Gadus morhua L.) and haddock (Melanogrammus aeglefinus L.) were subjected to 30 s air exposure stressors following acclimation to 4, 10 and 14 and 4, 8 and 14 degrees C respectively. Both species responded to the stressor with increases in plasma cortisol at all temperatures tested. At 14 degrees C cortisol levels peaked within 1 h post-stressor, and returned to pre-stressor levels within 24 h. In contrast, at 4 degrees C, peak cortisol levels were not attained until 6 h post-stressor in haddock and remained elevated beyond 24 h in both species. The rate of plasma glucose accumulation was greater at higher temperatures in both species and no increase was seen at 4 degrees C. Lysozyme activity in cod, in response to the stressor, was lower than the values reported for some other species and increased slightly at 14 degrees C. The results show that cod and haddock acclimated to different temperatures respond to common, acute stressors in a manner similar to other teleosts

Investigations of selected parameters for growth of larval and juvenile black sea bass Centropristis striata L.

The black sea bass Centropristis striata L. endemic to the U. S. Atlantic and Gulf of Mexico coasts is a highly sought species that commands a high price in the marketplace. Investigations were undertaken to determine the basic requirements for culture of sea bass larvae and juveniles. Adult black sea bass were captured from the wild and were found to be robust and to adapt well to captivity. Larvae were obtained by strip spawning of these adults and survived and grew at higher rates in seawater supplemented with algae (greenwater) and maintained at 22 C, than in seawater with or without supplemental algae at 18 C. Larvae were provided a diet of rotifers through 12 d post hatch (DPH) and weaned over a 3-d period to enriched Artemia replenished daily to a density of 10 individuals/mL. By 18 DPH, larvae began ingesting a formulated diet for marine finfish and were completely weaned from live feed by 25 DPH, which coincided with the onset of metamorphosis. Juveniles tolerated a range of salinity from 10-32 ppt with the highest growth rate observed at 20 ppt. Culture of larvae and juveniles on a commercial scale was successful using conditions similar to those employed in the laboratory. The findings presented here suggest the potential for commercial culture of this species in the USA