Length-weight relationship and condition factor of tropical sand goby, Acentrogobius caninus (Valenciennes 1837) from Pabean Bay, West Java, Indonesia

This study aims to determine the length-weight relationship (LWR) and evaluate the condition factors of the tropical sand goby, Acentrogobius caninus (Valenciennes 1837), in Pabean Bay West Java, Indonesia. The sampling was carried out once a month from January to December 2015, and during that period, 152 samples were collected. The LWR is W = 9 x 10-6 L-3.0356. The growth pattern of tropical sand goby is isometric (b=3). The monthly relative condition factor ranged from 0.798 to 1.322 (average: 1.028).

Seed production and grow-out of sand goby (Oxyeleotris marmoratus) in Vietnam.

Pond area for broodfish ranges from 500 to 1,000 m2 with a depth of 1-1.2 m. Broodfish density ranges from 0.2 to 0.3 kg m-2. Fresh food such as snails, small prawns and fish are used to feed broodfish at a feeding rate of 3.5% of total body weight per day. Water exchange is done periodically at 20-30% of total volume per time. Sticky eggs of sand goby adhere to substrates. Hatching takes place 22-48 hours after fertilization. A suitable temperature is 28-29°C and pH at 6.5-7.5. Nursing fry to fingerlings is carried out in ponds at a stocking density of 300-500 fish m-2. After nursing for 50-60 days, they can reach the size of 3 cm. Large fingerlings of 15-30 g are obtained after at least 3 months of nursing. Continuing nursing up to 5-6 months gives larger fingerlings (60-80 g) for grow-out. Stocking density is 5-10 fish m-2 in grow-out ponds and 30-40 fish m-2 in cages. Fish, small prawns, snails and by-products from slaughterhouses are used to feed the fish. They can reach a marketable size of 500 g or more after 6-7 months of culture.

Success and failure of sand goby culture.

The success in the seed production of the sand goby (Oxyeleotris marmorata) has contributed to the protection of natural resources and the availability of seed for aquaculture. About 30-50 million sand goby fingerlings are produced in hatcheries for domestic and export markets every year. Grow-out production systems of sand goby developed in the 1990s. It helped to increase the incomes of many fish farmers and contributed to the country's foreign exchange earnings. Constraints to hatchery-produced seed for grow-out have resulted in difficulties for sand goby seed producers. Hatchery-produced seed commands a higher price than wild seed and thus is not able to completely replace the natural seed supply. However, wild seed is of uneven size and capture methods are not standardized, resulting in the fish body being easily scratched, leading to disease and mortality. The fish is sensitive to changes in environmental conditions and vulnerable to diseases which are difficult to treat. The market for this species is also limited.

Ichthyoplankton of the South-Eastern Baltic Sea in the summer season: modern changes in the distribution and abundance of eggs and larvae of mass species

The aim of ichthyoplankton studies in July 2019 was to monitor the distribution and estimate the abundance of: 1) eggs and larvae of mass pelagophilous fish species (cod, sprat) in deep-water areas; 2) larvae of small-sized benthic fish species inhabiting the shallow coastal zone of the South-Eastern Baltic Sea (the exclusive economic zone of the Russian Federation). It was noted, the main concentrations of cod and sprat eggs were in the northern part of the area (southern slope of Gotland Deep). Aggregations with a noticeably lower abundance of eggs were observed in the Gdansk basin. In July 2019, the average abundance of cod eggs (3.4 ind./m2) was higher than in the years without strong North Sea advections according to observations in the 1990–2000. Although the reproduction of sprat was nearing completion, in July its eggs dominated the ichthyoplankton assemblage of the deep-water zone, tenfold exceeding the numbers of cod eggs. In the composition of the ichthyoplankton of the shallow-water zone, 7 species of fish larvae were found, among which the sand goby dominated in numbers. Its small-sized larvae were most abundant above depths from 20 to 40 m, which made it possible to identify this depth range as an area of intensive spawning of the species. The decrease in the number of sand goby larvae in the 2010s, compared to the beginning of the 2000s, could be associated with the spread of the Ponto-Caspian invader round goby in the coastal zone, small-sized fry of which were also found in July 2019 in the ichthyoplankton of the coastal zone.

Changes in the composition and abundance of ichthyoplankton along environmental gradients of the southern Baltic Sea

The research focuses mainly on the ichthyoplankton of the Baltic deeps – the inflow route from the North Sea. The ichthyoplankton was represented by eggs and larvae of nine fish species: sprat, cod, herring, European flounder, fourbeard rockling, longspined bullhead, straightnose pipefish, sand goby and great sandeel. The species composition of ichthyoplankton varied depending on the location of a given site – the number of taxa ranged from one to five. The Slupsk Furrow was the most diversified area in terms of the number of taxa, while the highest abundance of ichthyoplankton occurred in the Bornholm Basin. The sprat clearly dominated and inhabited all the surveyed depths. Of the remaining species, only cod eggs as well as eggs and larvae of the fourbeard rockling significantly contributed to this formation. They occurred within their main spawning grounds (Bornholm Deep in the near-bottom layers) and secondary spawning grounds (Slupsk Furrow and Gdansk Deep) where salinity and oxygenation of water favored their development. Biometric research has shown that the diameter of eggs was within the size range typical of the Baltic Sea.

Water turbidity constrains male mating success in a marine fish

Human-induced eutrophication, resulting in increased algal growth and water turbidity, is an alarming problem in aquatic systems. Many studies have focused on the effects of algal turbidity on mate choice and sexual selection in fish, but little emphasis has been given to the ways it can constrain mating success. Here we experimentally investigated the effects of algal turbidity on maximum male mating success and parental care in the sand goby, Pomatoschistus minutus, a fish with a resource-defence mating system and male parental care. For this purpose, we introduced to 1 nest-holding male 5 random-sized ripe females in either clear or in turbid water. After spawning, we observed how many mates and eggs the male received and followed his parental behaviour and egg survival for 6 days under turbid or clear water conditions. When spawning took place in clear water, the number of eggs the male received into his nest increased with the total weight of five females in his tank. However, when spawning took place in turbid water, there was no relationship between female size and the number of eggs laid, although the number of females that spawned was the same as in clear water. The results indicate that females adjust the number of eggs they lay according to water turbidity. This could explain previous findings that mating success is more evenly distributed among males in turbid than clear water conditions. Significance statement The first responses of animals to human-induced changes in the environment are behavioural. Subtle changes in the behaviour of individuals can have profound consequences for populations and communities. Human-induced eutrophication, leading to algal blooms and water turbidity, is a major environmental problem in aquatic systems worldwide. Our results on the sand goby suggest a new mechanism by which water turbidity may affect fish mating systems and weaken sexual selection. When spawning takes place in clear water, the number of eggs accumulated in a males’ nest is an increasing function of the fecundity of the females. However, when spawning in turbid water, this positive relationship between female size and egg numbers disappears. We believe this is because females do not perceive the competition from other females in turbid water and therefore invest less in present reproduction.

Pengaruh penggunaan jenis wadah yang berbeda terhadap pertumbuhan dan kelangsungan hidup ikan betutu (Oxyeleotris marmorata Blkr.)

AbstrakIkan betutu Oxyeleotris marmorata merupakan ikan lokal potensial menjadi komoditas budidaya. Performa pertumbuhan dan kelangsungan hidup dapat ditingkatkan dengan mengembangkan wadah budidaya. Tujuan penelitian adalah mengetahui jenis wadah budidaya yang optimal dalam mendukung pertumbuhan dan kelangsungan hidup. Perlakuan yang di uji adalah kolam tanah, kolam hapa dan kolam terpal berukuran 3 m x 2 m x 1 m. Ukuran benih yang digunakan 15±1,39 cm dengan bobot 250,04±1,70 g dengan padat tebar 25 ekor/kolam. Selama 120 hari masa pemeliharaan, pakan yang diberikan adalah ikan rucah sebanyak 30% dari bobot tubuh dengan frekwensi 2x sehari. Hasil penelitian menunjukkan perbedaan jenis wadah berpengaruh nyata terhadap pertambahan bobot dan laju pertumbuhan spesifik, namun tidak berpengaruh nyata terhadap kelangsungan hidup. Pertambahan bobot terbaik terdapat pada perlakuan jenis wadah kolam tanah sebesar 53,86±1,10 g dengan laju pertumbuhan spesifik 0,45±0,010 %bobot tubuh/hari dan kelangsungan hidup 85,33±6,11%. Kualitas air pada seluruh wadah pemeliharaan masih mendukung pertumbuhan dan kelangsungan hidup. Hasil penelitian ini dapat dijadikan informasi dasar dalam pemilihan wadah budidaya yang efektif dan efisien dalam pengembangan budidaya ikan betutu secara optimal.Kata kunci: ikan betutu; pertumbuhan; kelangsungan hidup; wadahAbstractSand goby (Oxyeleotris marmorata. Blkr) is a potential fish species for aquaculture in Indonesia. However, the growth and survival rate performance can be improved by developing cultivation containers. The research objective was to determine the optimal type of cultivation container to produce high growth and survival rate. The ponds treatments used in this experiment were soil pond, hapa pond and tarpaulin pond with measuring 3 m x 2 m x 1 m. The initial fish length average was 15±1.39 cm, with the initial body weight average of 250.04±1.70 g with the stocking density of 25 individual/pond. During 120 days of the rearing period, the fish were fed with trash fish with a proportion of 30% of body weight with the frequency of feeding 2x a day. The results showed differences in the type of container significantly affected weight gain and specific growth rates but did not significantly affect survival rate. The best weight gain was found in the treatment of soil pond containers at 53.86 ± 1.10 g with a specific growth rate of 0.45 ± 0.010% body weight/day and survival rate of 85.33 ± 6.11%. Water quality in all containers still supports growth and survival rate. The results of this study can be used as necessary information in the selection of effective and efficient aquaculture containers to produce optimal sand goby culture.Keywords: sand goby; growth; survival rate; container