Variations in reproductive potential between nearshore and offshore spawning contingents of hogfish in the eastern Gulf of Mexico

Hogfish, Lachnolaimus maximus (Walbaum), have multiple traits that confound measuring reproductive potential: they are protogynous, relatively long‐lived harem‐forming fish that spawn daily for months. Additionally, recent evidence demonstrates that size, age and timing of sex change vary on a spatial scale within the study area (West Florida shelf, USA). This study investigates the effect of this spatial variation on hogfish reproductive potential by evaluating spawning seasonality, spawning frequency and batch fecundity using an indeterminate egg production model. Offshore females were larger than nearshore females, and batch fecundity was related in a log‐linear manner to female size. Gonad histology demonstrated a more protracted reproductive period for females offshore (8 months) than nearshore (4 months). Spatial variations in size coincide with ontogeny because hogfish move offshore with growth; however, even after accounting for fish size, offshore females spawned more. In areas where male removal rates are elevated, spawning harems are disrupted; thus, greater fishing effort nearshore may further reduce the reproductive potential of these females. These nearshore and offshore spawning components of the population are not genetically distinct, but instead represent two contingent spawning strategies that likely enhance total population stability and resilience of this stock in the eastern Gulf of Mexico.     

Potential for reintroduction of lake sturgeon in five northern Lake Michigan tributaries: a habitat suitability perspective

• 1. Conservation and rehabilitation efforts for lake sturgeon Acipenser fulvescens throughout the Great Lakes include the re‐establishment of self‐sustaining stocks in systems where they have been extirpated.
• 2. Information on the suitability of potential lake sturgeon habitat in tributaries is important for determining their capacity to support lake sturgeon stocking and to develop system‐specific rehabilitation strategies.
• 3. Geo‐referenced habitat information characterizing substrate composition, water depth, and stream gradient were applied to a life‐stage specific lake sturgeon habitat suitability index in a geographic information system to produce spatially explicit models of life‐stage specific habitat characteristics in five northern Lake Michigan tributaries from which lake sturgeon have been extirpated.
• 4. Habitat models indicated that high quality lake sturgeon spawning and staging habitat comprised 0 to 23% and 0 to 9% of the available habitat, respectively, whereas high quality juvenile lake sturgeon habitat was relatively ubiquitous throughout each river and comprised 39 to 99%.
• 5. Comparison of these data to lake sturgeon habitat availability in Lake Michigan tributaries currently supporting populations indicated that spawning and staging habitats may limit the ability of these systems to support spawning. Efforts to re‐establish lake sturgeon populations in these systems should consider the creation of spawning and staging habitat to increase reproductive and recruitment potential prior to the initiation of stocking efforts.

Copyright © 2007 John Wiley & Sons, Ltd.     

Multiple spawning and related variations in female reproductive parameters of amphidromous type ayu

Adult ayu Plecoglossus altivelis were sampled from the Nezugaseki River, Yamagata Prefecture to investigate the reproductive parameters and analyze their variations related to multiple spawning. Ovarian histology (mainly based on the occurrence of postovulatory follicles) indicated that female ayu can be divided into four groups, which are considered to correspond with unspawned, once spawned, twice spawned, and three (or more) times spawned individuals. Comprehensive analysis of the ovarian state with field surveys revealed that most of the female ayu achieve second spawning and that third spawning is very common in this river. Mean relative batch fecundity (RBF) for the second, third, and fourth spawning indicated 69, 42, and 22%, respectively, of the value for the first spawning, showing a decline with the number of spawning batches. Mean gonadosomatic index (GSI) values of non-ovulating fish showed a similar decline during the main spawning period (October). Condition factor (without gonads) during autumn also decreased with the number of batches spawned, suggesting that multiple spawning is achieved partly by transfer of body mass nutrients to the ovary. Size dependency in reproductive parameters such as occurrence of the multiple spawning, RBF values, and GSI values of the unspawned fish, was not evident except for GSI values in early September (generally during the early phases of ovarian development), when larger fish had larger GSI.     

Reproductive performance in induced and spontaneous spawning of the mangrove red snapper, Lutjanus argentimaculatus: a potential candidate species for sustainable aquaculture

A reliable breeding technique was developed for the mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775), to help sustain the aquaculture of this immensely popular species in Southeast Asia. Using standardized indices of female maturity (based on mean oocyte diameter of ≥0.40 mm), time of injection (1000–1130) and sex ratio (one female to two males), a single injection of 100 μg kg^?1 luteinizing hormone‐releasing hormone analogue (LHRHa) (n=16 fish), but not 50 μg kg^?1 (n=five fish), successfully induced egg (62.5% success rate) and larval (43.8%) production. Human chorionic gonadotropin (hCG) at 500 IU kg^?1 (n=five fish) also failed to induce spawning, but doses of 1000 (n=22 fish) and 1500 IU kg^?1 (n=15 fish) gave spawning (77.3% and 80.0% respectively) and hatching success rates (72.7% and 60.0% respectively) that were not significantly different from those of 100 μg kg^?1 LHRHa. No spawning was observed in saline‐injected controls (n=seven fish). While mean spawning latency, egg diameter, egg production per spawn, percent egg viability, hatching rate, percent of normal larvae and cumulative survival of eggs to normal larvae did not differ significantly among the effective hormones and doses, 1000 IU kg^?1 hCG had a higher percentage (76.5%) of total spawns with egg production per spawn in excess of one million than those of 1500 IU kg^?1 hCG (50.0%) and 100 μg kg^?1 LHRHa (40.0%). Mangrove red snapper spontaneously spawned from March–April to November–December with a peak of egg collection and spawning in May–June. Egg collection per spawn ranged from 0.05 to 6.35 million. Spontaneous spawning of mangrove red snapper exhibited lunar periodicity with spawns mostly occurring 3 days before or after the last quarter and new moon phases and occurred consistently between 02:00 and 04:00 hours. High fecundity and good egg quality, coupled with the ability to respond to induce spawning or natural spawning in captivity, provide a sound basis for improving the sustainability of red snapper aquaculture in Southeast Asia.     

Introducing size limits as a management tool for the recreational line fishery of silver kob, Argyrosomus inodorus (Griffiths and Heemstra), in Namibian waters

Individual silver kob Argyrosomus inodorus (Griffiths and Heemstra) first mature at just over 1 yr of age and the median age at maturity is approximately 1.5 yr. Spawning of silver kob was observed in the southern and central region of the stock's range, but little spawning activity was found in silver kob sampled from the northern region. The spawning period is protracted over 6 months (October–March), which coincides with warmer water temperatures (>15 °C) and the occurrence of large-sized spawning silver kob in the southern and central part of Namibia. Implementing a minimum size limit for the silver kob fishery is not recommended as it will have serious economic implications for the coastal communities. The protection of the spawning areas, Meob Bay and Sandwich, should be continued and a strict bag limit on large-sized silver kob is recommended for the Namibian silver kob recreational fishery.     

The determination of ecological status in shallow lakes — a tested system (ECOFRAME) for implementation of the European Water Framework Directive

• 1. The European Water Framework Directive requires the determination of ecological status in European fresh and saline waters. This is to be through the establishment of a typology of surface water bodies, the determination of reference (high status) conditions in each element (ecotype) of the typology and of lower grades of status (good, moderate, poor and bad) for each ecotype. It then requires classification of the status of the water bodies and their restoration to at least ‘good status’ in a specified period.
• 2. Though there are many methods for assessing water quality, none has the scope of that defined in the Directive. The provisions of the Directive require a wide range of variables to be measured and give only general guidance as to how systems of classification should be established. This raises issues of comparability across States and of the costs of making the determinations.
• 3. Using expert workshops and subsequent field testing, a practicable pan‐European typology and classification system has been developed for shallow lakes, which can easily be extended to all lakes. It is parsimonious in its choice of determinands, but based on current limnological understanding and therefore as cost‐effective as possible.
• 4. A core typology is described, which can be expanded easily in particular States to meet local conditions. The core includes 48 ecotypes across the entire European climate gradient and incorporates climate, lake area, geology of the catchment and conductivity.
• 5. The classification system is founded on a liberal interpretation of Annexes in the Directive and uses variables that are inexpensive to measure and ecologically relevant. The need for taxonomic expertise is minimized.
• 6. The scheme has been through eight iterations, two of which were tested in the field on tranches of 66 lakes. The final version, Version 8, is offered for operational testing and further refinement by statutory authorities.

Copyright © 2003 John Wiley & Sons, Ltd.     

The potential of deoiled sal (Shorea robusta) seed meal as a feedstuff in pelleted feed for Indian major carp, rohu, Labeo rohita (Hamilton), fingerlings

Ten isonitrogenous (350 g kg^1-crude protein) diets incorporating raw and soaked deoiled sal (Shorea robusta) seed meal at 200, 300,400, 500 and 600 g kg^?1 into a fish-meal-based diet were fed to rohu, Labeo rohita (Ham.), fingerlings for 60 days and fish performance was studied. Tannin from raw salseed meal could be reduced from 34 to 7 g kg^?1 by soaking in water for 16 h at room temperature. In terms of growth response, food conversion ratio and protein efficiency ratio, a diet containing 200 g kg^?1 soaked salseed meal resulted in significantly (P < 0.01) the best performance of the fish. Apparent protein digestibility (APD) values decreased with increasing level of oilseed meal. Carcass protein was highest in fish fed diets containing 200 g kg^?1 soaked salseed meal. The results showed that deoiled salseed meal can be incorporated in carp diets up to 200 g kg^?1 and 300 g kg^?1 in raw and treated forms respectively.     

Validation of processed animal proteins (mono‐PAPS) in experimental diets for juvenile gilthead sea bream (Sparus aurata L.) as primary fish meal replacers within a European perspective

Experimental diets were formulated to evaluate a “pure” poultry meat meal (PMM) source in diets formulated for juvenile gilthead sea bream (Sparus aurata L.). The digestible protein contribution of fish meal in a control diet was substituted by 25%, 50% and 75% of a processed poultry meat meal (PMM) on a digestible crude protein (DCP) basis and by 5% and 10% for an enzyme‐treated feather meal (EFM) and also a spray‐dried haemaglobin meal (SDHM), respectively. In a consecutive trial, diets were designed to assess the value of a “pure” (defatted) poultry protein substituting the fish meal (FM) protein content. Experimental diets included: a control diet, two test diets where 75% of FM was replaced by a full‐fat PMM (PMM75) or a defatted grade of PMM (dPMM75) and two test diets where 50% of FM was substituted for defatted PMM (dPMM50) or a 50:50 blend of soya bean meal and defatted PMM (SBM/dPMM) to produce a composite product. This soya bean/dPMM blend was tested to enhance the nutritional value of this key plant ingredient commonly employed in sea bream diets that can be deficient in specific amino acids and minerals. In the first trial, gilthead sea bream grew effectively on diets containing up to the 75% replacement of FM attaining a mean weight of 63.6 g compared to 67.8 g for the FM control fed group. For the consecutive trial, the fishmeal‐based control diet yielded the highest SGR followed by dPMM50 and SBM/dPMM blend inclusion but was not significant. Carcass FA profiles of gilthead sea bream conformed to the expected changes in relation to the dietary FA patterns, with the 18:1n‐9 representative of the poultry lipid signature becoming more apparent with PMM inclusion. The ratio of n‐3/n‐6 fatty acids was greatly affected in sea bream fed the full‐fat PMM at 75% inclusion due to fish oil exclusion. Defatted dPMM, however, allowed more of the fish oil to be used in the diet and reducing this latter effect in sea bream carcass, hence restoring the higher total omega‐3 HUFA fatty acids namely EPA and DHA and n‐3/n‐6 ratio. It is concluded that poultry meat meal can be modestly incorporated into formulated diets for sea bream and can be used in conjunction with soya bean meal without any fundamental changes in performance and feed efficiency.     

Development of a black sea bream fibroblast cell line and its potential use as an <Emphasis Type="Italic">in vitro</Emphasis> model for stress protein studies

A fibroblast cell line (BSF) derived from a caudal fin explant of black sea bream (Mylio macrocephalus) was developed. The optimum fetal bovine serum (FBS) concentration for fibroblast cell line growth was found to be 15–20% v/v FBS and the optimum temperature range for growth was found to be 26–30 °C. The fibroblast cells displayed a diverse distribution in chromosome number with two modal chromosome numbers of 48 and 54. Upon acute heat shock (+8 °C) the cells displayed a 4.1 fold increase in hsp70 and this elevation was not prolonged as hsp70 returned to near basal levels following a 6 h recovery period. The effect of the hsp70 inducer L-azetidine- 2-carboxylic acid was tested and it was found that at a concentration of 10 mM this inducer caused a 2.3 fold increase in hsp70 levels. The sensitivity of the fibroblast cell line to heavy metal exposure was tested by treatment with Cu2+ and it was found that hsp70 was significantly elevated in the presence of micromolar concentrations of Cu2+. The data from this study demonstrates that the established black sea bream fibroblast cell line could serve as a useful in vitro model for stress protein studies.