Assessment of plastic ingestion by pole-caught pelagic predatory fish from O'ahu,Hawai'i

1. Although the frequency of occurrence of plastic ingestion in the large-sized dolphinfish and tunas taken by the Hawai'i longline fishery is very low (frequency of occurrence < 5% of sampled individuals), the ingestion of plastic in smaller-sized specimens caught with pole-and-line gear by commercial and recreational fishers has not been investigated.
2. This study examined ingestion of >0.25 mm marine plastic debris (MPD) by four predatory fish species caught by commercial fishers around the Main Hawaiian Islands, and documented ingestion in three species: 85.7% of albacore tuna (n = 7), 40.0% of skipjack tuna (n = 10) and 12.5% of dolphinfish (n = 8).
3. Yellowfin tuna (n = 10) did not contain any MPD, probably owing to the high proportion of empty stomachs (60%).
4. For skipjack tuna, the frequency of occurrence of MPD ingestion was significantly higher for the smaller-sized specimens caught with pole-and-line (40%), compared with the larger-sized specimens caught with longlines (0%).
5. For dolphinfish, the frequency of occurrence of MPD ingestion was similar for the similar-sized specimens caught with pole-and-line and with longlines.
6. The ingested MPD items were micro–meso plastics, between 1 and 25 mm. While most ingested items were fragments, albacore also ingested line and skipjack also ingested sheets.
7. The predatory fishes ingested light MPD items that float in sea water, but there were species-specific differences in their polymer composition: albacore contained more polypropylene and polyethylene, and skipjack contained more elastomers, characterized by a high percentage of ester plasticizers.
8. Altogether, these results suggest that albacore and skipjack tunas ingest plastic of different types and polymers. Yet more research is needed to understand how differences in vertical distribution, foraging ecology and diet influence the MPD sampled by these predatory fish species.

     

Fatty Acid Composition of U.S. West Coast Albacore Tuna (Thunnus alalunga) and the Effects of Canning and Short-Term Storage

ABSTRACT

Changes in the fatty acid composition of 13 bled and blast-frozen U.S. West Coast albacore tuna (Thunnus alalunga) were determined following custom-canning and 5 weeks of canned storage. In accordance with typical custom-canning procedures, no additional packing materials were used, and the product did not undergo a precooking step. Raw albacore tuna was found to be rich in n-3 polyunsaturated fatty acids (PUFAs), with an average of 9.1% (% wt of total fatty acids) EPA and 33.8% DHA. Canning and short-term storage did not cause major fluctuations in the fatty acid profiles of the albacore tuna, with no significant changes in the total fractions of saturated fatty acids (30–31%), monounsaturated fatty acids (19%), PUFAs (50%), or n-3 PUFAs (46–47%). On a tissue weight basis, U.S. West Coast albacore tuna was found to contain high levels of total n-3 PUFAs, with 3.3 g/100 g tissue in raw tuna and 4.0–4.1 g/100 g tissue in products that were canned and stored for 5 weeks.     

Food consumption of tuna in the Equatorial Atlantic ocean: FAD-associated versus unassociated schools

Since 1991, fishing operations on tuna schools associated with drifting Fish Aggregating Devices (FADs) have become widespread in the purse seine fishery in the Gulf of Guinea. In the offshore South Sherbro area (0–5° N, 10–20° W), FAD-associated catches represent about 75 % of the total catch. This FAD fishery exploits concentrations of skipjack mixed with a smaller amount of bigeye and yellowfin tuna of similar size (46 cm), and some large yellowfin. Catches on unassociated tuna schools are mainly composed of large yellowfin in breeding phase and skipjack. Here we studied tuna diet in relation with the aggregation mode (FAD-associated or unassociated tuna schools), species, and size. The stomach contents of around 800 fish were analysed. Numerous empty stomachs were found, especially in fish caught under FADs. Diets were similar for all small-size tuna sharing the same aggregation type. Small tuna mainly feed on Vinciguerria nimbaria (Photichthyidae), a mesopelagic fish of the micronekton, whereas large tuna mainly feed on Scombridae, mixed with Cubiceps pauciradiatus (Nomeidae) when they were caught in unassociated schools. The feeding habits of tuna are discussed with emphasis on the behavior of V. nimbaria. Estimations of the daily ration of similarly sized tuna with the same aggregation mode were very close. The low estimated rations for small, FAD-associated tuna show that logs do not have a trophic function, but rather are a refuge. In contrast, FADs seem to influence the diet of large tuna because of the Scombridae prey that probably is associated to the FAD.     

Goussia auxidis (Dogiel, 1948) (Apicomplexa: Calyptosporidae) from tuna (Pisces: Scombridae) in the South Pacific

Abstract. A coccidian identified as Goussia auxidis (Dogiel, 1948) is recorded for the first time from the liver and spleen of albacore, Thunnus alalunga; the liver of slender tuna, Allothunnus fallai , skipjack tuna, Katsuwonus pelamis and yellowfin tuna, T. albacares: and in the spleen of Scomber australasicus. All host fish were caught in the western and central South Pacific Ocean. Coccidian spores were not found in the liver of southern bluefin tuna, T. maccoyii , or butterfly tuna, Gasterochisma melampus.     

Distribution of albacore (Thunnus alalunga) in the Indian Ocean and its relation to environmental factors

The distribution pattern of albacore, Thunnus alalunga, in the Indian Ocean was analyzed based on catch data from the Taiwanese tuna longline fishery during the period 1979–85. The Taiwanese tuna fishery began operating in the Indian Ocean in 1967. We used a geographic information system to compile a fishery and environmental database and statistically explored the catch per unit effort (CPUE) distribution of albacore. Our results indicated that immature albacore were mainly distributed in areas south of 30°S although some displayed a north–south seasonal migration. Mature albacore, which were mainly concentrated between 10°S and 25°S, also showed a north–south migration. Within 10°S and 30°S, the separation of mature, spawning, and immature albacore life history stages roughly coincided with the boundaries of the three oceanic current systems in the Indian Ocean. The optimal environmental variables for CPUE prediction by stepwise discriminant analysis differed among life history stages. For immature albacore, the sea surface variables sea surface temperature (SST), chlorophyll concentration and surface salinity were significant. For mature albacore, SST was significant, while for spawning albacore, the sub‐surface variables temperature at 100 m and oxygen at 200 m were significant. Spawning albacore evidently prefer deep oceanographic conditions. Our results on the oceanographic conditions preferred by different developmental stages of albacore in the Indian Ocean were compatible with previous studies found in the Pacific Ocean.     

Dissolved nutrient release from solid wastes of southern bluefin tuna (Thunnus maccoyii, Castelnau) aquaculture

Finfish pens are point sources of dissolved nutrients released from fish metabolism or degradation of solid wastes. Nutrients leaching from uneaten feed and faeces are not usually quantified in mass budgets for these systems, leading to an overestimation of fish retention or deposition to the seabed. In this study, we investigated nutrient leaching from pellets and baitfish feed as well as faeces of southern bluefin tuna (Thunnus maccoyii) into seawater. Faeces were nitrogen depleted (51–54 mg N g⁻¹ dw) and phosphorus enriched (62–72 mg P g⁻¹ dw) compared with feeds (83–111 mg N g⁻¹ dw and 17–21 mg P g⁻¹ dw). Less phosphorus was available for leaching from pellets and faeces of pellet‐fed tuna (5–6%) than from baitfish and faeces of baitfish‐fed tuna (17–21%). The proportion of soluble nitrogen in pellets (15%) was also lower than in baitfish and faeces (35–43%). Leaching loads for a feed conversion ratio of 5 were estimated as 22 and 26 kg N tonne⁻¹ growth when baitfish or pellets were used as feed respectively. Phosphorus loads were estimated as 15 and 4 kg P tonne⁻¹ growth respectively. More than 90% of nitrogen loads, and approximately 50% of phosphorus, are likely to be released into seawater before solid wastes reach the seafloor.     

金枪鱼延绳钓环形钩和圆形钩钓获率比较

根据"华远渔18号"和"华远渔19号"两艘冰鲜金枪鱼延绳钓渔船2005年9月15日~12月12日在印度洋热带公海水域(0°47′~10°16′N,61°40′~70°40′E)作业期间收集的数据,以每千钩钓获尾数和平均净重,对环型钩与圆型钩对大眼金枪鱼和黄鳍金枪鱼的选择性、钓获率差异等进行了比较研究。结果表明:不同钓具漂移速度下环型钩与圆型钩各自对大眼金枪鱼和黄鳍金枪鱼的选择性无显著差异;不同钓具漂移速度下环型钩与圆型钩之间对大眼金枪鱼和黄鳍金枪鱼的钓获率无显著差异;环型钩与圆型钩之间对大眼金枪鱼和黄鳍金枪鱼渔获物净重无显著差异。     

Estimating digestible protein requirements of silver perch, Bidyanus bidyanus Mitchell

In this study, we estimated requirements for digestible protein, using intact protein sources, at one digestible energy content. Using digestibility data for silver perch (Bidyanus bidyanus Mitchell) for a large number of ingredients, we formulated a ‘summit’ diet to contain between 1.4 and 1.8 times the ‘expected requirements’ for digestible essential amino acids (based on requirements for channel catfish, Ictalurus punctatus Rafinesque). A ‘diluent’ diet was formulated to contain 0.4–0.5 times the expected requirements of digestible essential amino acids. Both ‘summit’ and ‘diluent’ diets contained similar digestible energy (14.7 MJ digestible energy kg^?1 for the summit and 13.4 MJ digestible energy kg^?1 for the diluent). Six diets were prepared with the following amounts of summit–diluent diets: 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100. A practical diet widely used by commercial farmers was also included as a control. Ten juvenile fish (2.1–2.6 g) were stocked into each experimental 70‐L acrylic aquarium, and each dietary treatment was randomly assigned to five replicate aquaria. Fish were fed twice daily to apparent satiation for 54 days. Final individual fish weight ranged from 4–15.5 g. Results were analysed using intersecting linear regression analysis. The optimum digestible dietary protein for diets with 13.4–14.7 MJ digestible energy kg^?1, after which protein deposition did not increase significantly, was 28%. Although this study did not determine requirements for individual amino acids, for diets with the digestible energy content used here, requirements for individual amino acids obviously did not exceed the content in the 28% protein diet. These contents are useful as an estimate of ‘recommended levels’ for silver perch diets with 13.4–14.7 MJ digestible energy kg^?1. The proximate composition of fish was affected by diet. Whole body protein and moisture increased, whereas lipid content decreased with increasing dietary protein content (and increasing protein–energy ratio and decreasing lipid). Fish size was also affected by diet; however, the changes in whole carcass proximate composition also occurred for fish fed diets 60:40, 80:20 and the summit diet which were a similar final weight.     

Comparison of the lipid profiles from wild caught eggs and unfed larvae of two scombroid fish: northern bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis> L., 1758) and Atlantic bonito (<Emphasis Type="Italic">Sarda sarda</Emphasis> Bloch, 1793)

Lipids and essential fatty acids are determinants of the reproductive process in marine fish, affecting fecundity, egg quality, hatching performance, pigmentation and larval malformation. We have analyzed and characterized the lipids of eggs and unfed larvae of two wild caught scombroid fish, the Atlantic northern bluefin tuna (Thunnus thynnus) and Atlantic bonito (Sarda sarda). Dry matter and total lipid contents, polar and neutral lipid classes and total lipid fatty acid contents were determined in the eggs of bluefin tuna and eggs and unfed larvae during the development of Atlantic bonito. Bluefin tuna eggs had slightly but significantly more dry mass than bonito eggs but very similar lipid content. However, bluefin tuna eggs presented a higher polar lipid content due to increased proportions of phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). Bonito eggs and larvae showed increasing dry mass and decreasing lipid content with development. The proportion of polar lipids increased due to increased PE, PS and PI, whereas choline-containing polar lipids (phosphatidylcholine and sphingomyelin) remained relatively constant. Free cholesterol also increased, whereas the levels of other neutral lipids, especially triacylglycerol and steryl ester fractions, decreased, presumably due to utilization for energy to drive development. Bluefin tuna eggs had higher levels of n − 3 and n − 6 highly unsaturated fatty acids due to higher docosahexaenoic and arachidonic acid contents, respectively, than bonito eggs. The results are discussed in relation to the lipid and fatty acid requirements of larval scombroid fish in comparison to those of other larval marine finfish species under culture conditions.     

北太平洋长鳍金枪鱼年龄与生长初步研究

北太平洋长鳍金枪鱼(Thunnus alalunga)是金枪鱼渔业的主要捕捞对象之一,其资源的养护和管理日益受到各方关注,鱼类年龄鉴定是渔业资源研究的重要内容之一。根据2013~2014年北太平洋长鳍金枪鱼探捕所采集的227个脊椎骨样本,用不同的染色方法分成4组进行年龄的鉴定,选用线性模型、指数模型和幂指数模型对叉长和脊椎骨半径进行拟合,最后选出结果最好的鉴定组和拟合模型,通过年龄鉴定估算长鳍金枪鱼的Von Bertalanffy生长方程。研究结果表明,北太平洋长鳍金枪鱼的叉长范围为52~104 cm,优势叉长组为81~90 cm,占总数的83.1%;年龄组成以5、6龄较多,占样本总数的80.86%。最终得到北太平洋长鳍金枪鱼生长方程为:Lt=109.180 2[1-e~(-0.258 783(t-1.991 28))],t_(tp)=2.25。     

Standardizing catch and effort data of the Taiwanese distant-water longline fishery in the western and central Pacific Ocean for bigeye tuna, Thunnus obesus

Catch per unit effort (CPUE) is often used as an index of relative abundance in fisheries stock assessments. However, the trends in nominal CPUE can be influenced by many factors in addition to stock abundance, including the choice of fishing location and target species, and environmental conditions. Consequently, catch and effort data are usually ‘standardized’ to remove the impact of such factors. Standardized CPUE for bigeye tuna, Thunnus obesus, caught by the Taiwanese distant-water longline fishery in the western and central Pacific Ocean (WCPO) for 1964–2004 were derived using three alternative approaches (GLM, GAM and the delta approach), and sensitivity was explored to whether catch-rates of yellowfin tuna and albacore tuna are included in the analyses. Year, latitude, and the catch-rate of yellowfin explained the most of the deviance (32–49%, depending on model configuration) and were identified consistently among methods, while trends in standardized catch-rate differed spatially. However, the trends in standardized catch-rates by area were found to be relatively insensitive to the approach used for standardization, including whether the catch-rates of yellowfin and albacore were included in the analyses.     

Effects of dietary fish oil replacement on growth and carcass proximate composition of juvenile barramundi (Lates calcarifer)

An experiment was carried out to determine the effects of dietary fish oil replacement at an optimal level on the growth and carcass proximate composition of juvenile barramundi or sea bass (Lates calcarifer). Ten fish feeds were formulated to contain iso‐ingredients with theoretically identical dietary lipid levels but with different sources of lipids (fish oil, soybean oil, canola oil and linseed oil) replacing dietary fish oil. Three hundred fish were equally divided into 30 70‐L plastic tanks (three replicate tanks for each treatment). Fish were fed with experimental diets for 40 days within closed recirculating freshwater systems (70 L h^?1, 28°C and 12L:12D). Growth, specific growth rate, food conversion ratio (FCR) and carcass proximate composition were determined. Dietary lipids significantly affected (P<0.05) the growth of the fish. Good growth and low FCR were observed in all treatments. Therefore, fish oils can be partially replaced by vegetable oils to reduce the feed cost. There were no significant differences (P>0.05) in lipid, moisture and protein content in fish carcasses among the group. However, juvenile barramundi showed increasing lipid and moisture content in muscle, whereas decreasing protein content when compared to the initial fish.     

北太平洋长鳍金枪鱼卵巢的发育特征

根据2013年10月–2014年2月在北太平洋海域(29°08′~41°08′N,163°50′~144°19′W)采集的364尾长鳍金枪鱼的卵巢样本,利用组织学分析,详细描述了长鳍金枪鱼卵巢、卵细胞的发育阶段。结果显示,北太平洋长鳍金枪鱼卵巢内同时存在不同时相的卵细胞,为分批产卵类型;组织学上,长鳍金枪鱼的卵细胞发育过程分为6个时相,卵巢发育过程分为6个时期;卵巢成熟指数在成熟期为Ⅰ~Ⅴ期时逐渐增大,在Ⅵ期时减小;北太平洋长鳍金枪鱼产卵高峰为12月中旬和1月初,其卵巢成熟指数随纬度的升高呈递减趋势,随经度变化规律不明显。研究表明,通过对北太平洋长鳍金枪鱼卵巢的发育特征的分析与探讨,可为北太平洋长鳍金枪鱼的资源状况评估及渔业可持续发展提供生物学信息。     

印度洋长鳍金枪鱼资源评估的影响因素分析

多个模型被用于印度洋长鳍金枪鱼(Thunnus alalunga)的资源评估,但这些模型的评估结果均存在较大的不确定性,为此,本文对影响印度洋长鳍金枪鱼资源评估的因素进行了分析。分析结果认为:(1)由于渔业数据存在不报、漏报或混报及采样样本数过低、采样协议出现变化等问题,造成印度洋长鳍金枪鱼渔业的渔获量、体长组成或年龄组成数据存在质量问题;(2)尽管对单位捕捞努力渔获量(catch per unit effort,CPUE)进行了标准化,但目标鱼种变化及捕捞努力量空间分布变化仍严重影响了标准化CPUE数据的质量;(3)印度洋长鳍金枪鱼的种群生态学及繁殖生物学研究仍比较薄弱,种群结构、繁殖、生长、自然死亡信息比较缺乏,在资源评估中,相关参数设置需借用其他洋区的研究结果;(4)海洋环境对印度洋长鳍金枪鱼的资源变动与空间分布具有显著影响,但评估模型较少考虑海洋环境的影响。由于上述问题的存在,导致当前评估结果存在较大不确定性。未来,应继续探索提高资源评估质量的方法,同时研究建立管理策略评价框架,以避免渔业资源评估结果的不确定性对该渔业可持续开发的影响。     

Vertical behavior of juvenile yellowfin tuna Thunnus albacares in the southwestern part of Japan based on archival tagging

The behavior of juvenile yellowfin tuna Thunnus albacares in southwestern Japan was investigated using archival tag data from five fish (fork length 52.5–92 cm, days at liberty 26–280 days) released near the Nansei Islands (24–29°N, 122–130°E). Vertical behavior was classified into three patterns: “shallow” (≥50 % of daytime hours at depth of <50 m), “deep” (≥50 % of daytime hours at ≥100 m), and “intermediate” (other than “shallow” or “deep”). The pooled proportion of the number of days of each behavior was 29, 25 and 46 %, respectively. The proportion of “shallow” behavior increased with fish size. The proportion of time spent near the surface at nighttime increased in the colder season, when the thermal gradient was relatively small. Surface-oriented behavior (fish remained at a depth of <10 m for more than 10 min) occurred mainly during nighttime and between November and January. Dives exceeding 500 m were occasionally observed (0.02 day^?1), and one fish dived to 1230 m. The results of our study show that yellowfin tuna were typically distributed in the mixed layer or upper thermocline where the water temperature was close to the sea surface temperature and that the vertical behavior was variable.     

Dynamic Viscoelastic Properties of Tilapia (Oreochromis niloticus) Skin Gelatin

ABSTRACT

The viscoelastic properties of gelatin extracted from tilapia skin (protein yield: 21.2%) were evaluated using dynamic rheology tests. The flow curves of tilapia gelatin sols (1.0–6.6% w/w, 40°C; 0.5%, 2–40°C) complied with the Herschel-Bulkley model (R² = 0.92–0.99), indicating the presence of yield stress, while the gelling and melting temperature of gelatin dispersions (1.0–6.6%) fit well with the Eldridge-Ferry model (R² = 0.97). Tilapia skin gelatin displayed good thermo-stability and strong gel-forming properties, showing great potential as an alternative for mammal-based gelatin applied in various food products.     

Prevalence,intensity and pathology of the nasal parasite Nasicola hogansi in Atlantic bluefin tuna (Thunnus thynnus)

Ectoparasitic flatworms of Nasicola (Monogenoidea: Capsalidae), which infect nasal epithelium of true tunas (Thunnus spp.), are not well studied, nor have their impacts on the host's olfactory organ been evaluated. Infections of Nasicola hogansi on Atlantic bluefin tuna, Thunnus thynnus, were investigated with emphasis on the relationship between infection prevalence, abundance and mean intensity with bluefin tuna size, sex, body condition and capture month, as well as histopathological effects. Commercially caught Atlantic bluefin tuna (n = 161, 185–305 cm curved fork length) from the Gulf of Maine were sampled during June through August 2009 for infections by N. hogansi. A total of 247 specimens of N. hogansi were collected, with a prevalence of 45.3%, mean abundance of 1.57 (CI: 1.21–2.03) and mean intensity of 3.45 (CI: 2.91–4.22). Neither fish sex nor landing month had a significant effect on parasite parameters. Larger and better-conditioned Atlantic bluefin tuna had a higher mean intensity of infection. Pathology associated with infection by N. hogansi included extensive necrosis, sloughing of the nasal epithelium and associated inflammation of underlying connective tissues. Further epidemiological and pathological study of this host–parasite system is warranted since impaired olfaction, if present, could adversely affect spawning and migration of this top ocean predator.     

Near infrared reflectance spectroscopy in the prediction of chemical characteristics of minced raw fish

Near infrared reflectance spectroscopy (NIRS) was applied to predict chemical composition in minced raw fish samples used to make fishmeal. The coefficients of determination (R²_calibration) and standard error in cross validation (SECV) were 0.99 (3.86) and 0.96 (8.01) in g kg^–1 for moisture and oil, respectively. Total volatile nitrogen (TVN) gave R²_calibration and SECV of 0.96 (3.51) in mg g^–1. Temperature also was predicted by NIRS, yielding R²_calibration: 0.98 and SECV: 1.07 °C. We conclude that NIRS can be used successfully to assess the chemical composition and storage conditions in minced raw fish used by the fishmeal industry.     

Characterization and ontogenetic development of digestive enzymes in Pacific bluefin tuna Thunnus orientalis larvae

The major digestive enzymes in Pacific bluefin tuna Thunnus orientalis larvae were characterized, and the physiological characteristics of the enzymes during early ontogeny were clarified using biochemical and molecular approaches. The maximum activity of trypsin (Try), chymotrypsin (Ct) and amylase (Amy) was observed at pH 6–11, 8–11 and 6–9, respectively. Maximum activity of Try, Ct and Amy occurred at 50 °C, that of lipase (Lip) was at 60 °C and that of pepsin (Pep) was at 40–50 °C. These pH and thermal profiles were similar to those for other fish species but differed from those previously reported for adult bluefin tuna. Enzyme activity for all enzymes assayed was found to decrease at high temperatures (Try, Ct, Amy and Pep: 50 °C; Lip: 40 °C), which is similar to findings for other fish species with one marked exception—increased Try activity was observed at 40 °C. Lip activity appeared to be dependent on bile salts under our assay conditions, resulting in a significant increase in activity in the presence of bile salts. Ontogenetic changes in pancreatic digestive enzymes showed similar gene expression patterns to those of other fish species, whereas marked temporal increases in enzyme activities were observed at 10–12 days post hatching (dph), coinciding with previously reported timing of the development of the pyloric caeca in bluefin tuna larvae. However, complete development of digestive function was indicated by the high pep gene expression from 19 dph, which contradicts the profile of Pep activity and previously reported development timing of the gastric gland. These findings contribute to the general knowledge of bluefin tuna larval digestive system development.     

Relationship between prey utilization and growth variation in hatchery‐reared Pacific bluefin tuna,Thunnus orientalis (Temminck et Schlegel), larvae estimated using nitrogen stable isotope analysis

In mass culture of Pacific bluefin tuna Thunnus orientalis, a marked growth variation is observed after they start feeding at 6–7 mm in body length (BL) on yolk‐sac larvae of other species, and the growth variation in tuna larvae is a factor leading to the prevalence of cannibalism. To examine the relationship between prey utilization and growth variation, nitrogen stable isotope ratios (δ¹⁵N) of individual larvae were analysed. A prey switch experiment was conducted under two different feeding regimes: a group fed rotifers (rotifer fed group), and a group fed yolk‐sac larvae of spangled emperor, Lethrinus nebulosus (fish fed group) from 15 days after hatching (6.87 mm BL). The fish fed group showed significantly higher growth than the rotifer fed group. Changes in the δ¹⁵N of the fish fed group were expressed as an exponential model and showed different patterns from those of the rotifer fed group. The δ¹⁵N of fast‐growing tuna larvae collected in an actual mass culture tank after the feeding of yolk‐sac larvae was significantly higher than those of the slow‐growing larvae, indicating that slow glowing larvae depended largely on rotifers rather than the yolk‐sac larvae.